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1.
  • Veres, P., et al. (författare)
  • Observation of inverse Compton emission from a long gamma-ray burst
  • 2019
  • Ingår i: Nature. - : NATURE PUBLISHING GROUP. - 0028-0836 .- 1476-4687. ; 575:7783, s. 459-
  • Tidskriftsartikel (refereegranskat)abstract
    • Long-duration gamma-ray bursts (GRBs) originate from ultra-relativistic jets launched from the collapsing cores of dying massive stars. They are characterized by an initial phase of bright and highly variable radiation in the kiloelectron volt-to-mega electronvoltband, which is probably produced within the jet and lasts from milliseconds to minutes, known as the prompt emission(1,2). Subsequently, the interaction of the jet with the surrounding medium generates shock waves that are responsible for the afterglow emission, which lasts from days to months and occurs over a broad energy range from the radio to the gigaelectronvolt bands(1-6). The afterglow emission is generally well explained as synchrotron radiation emitted by electrons accelerated by the external shock(7-9). Recently, intense long-lasting emission between 0.2 and 1 teraelectronvolts was observed from GRB 190114C(10,11). Here we report multifrequency observations of GRB 190114C, and study the evolution in time of the GRB emission across 17 orders of magnitude in energy, from 5 x 10(-6) to 10(12) electronvolts. We find that the broadband spectral energy distribution is double-peaked, with the teraelectronvolt emission constituting a distinct spectral component with power comparable to the synchrotron component. This component is associated with the afterglow and is satisfactorily explained by inverse Compton up-scattering of synchrotron photons by high-energy electrons. We find that the conditions required to account for the observed teraelectronvolt component are typical for GRBs, supporting the possibility that inverse Compton emission is commonly produced in GRBs.
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2.
  • Smartt, S. J., et al. (författare)
  • A kilonova as the electromagnetic counterpart to a gravitational-wave source
  • 2017
  • Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 551:7678, s. 75-
  • Tidskriftsartikel (refereegranskat)abstract
    • Gravitational waves were discovered with the detection of binary black-hole mergers(1) and they should also be detectable from lower-mass neutron-star mergers. These are predicted to eject material rich in heavy radioactive isotopes that can power an electromagnetic signal. This signal is luminous at optical and infrared wavelengths and is called a kilonova(2-5). The gravitational-wave source GW170817 arose from a binary neutron-star merger in the nearby Universe with a relatively well confined sky position and distance estimate(6). Here we report observations and physical modelling of a rapidly fading electromagnetic transient in the galaxy NGC 4993, which is spatially coincident with GW170817 and with a weak, short.-ray burst(7,8). The transient has physical parameters that broadly match the theoretical predictions of blue kilonovae from neutron-star mergers. The emitted electromagnetic radiation can be explained with an ejected mass of 0.04 +/- 0.01 solar masses, with an opacity of less than 0.5 square centimetres per gram, at a velocity of 0.2 +/- 0.1 times light speed. The power source is constrained to have a power-law slope of -1.2 +/- 0.3, consistent with radioactive powering from r-process nuclides. (The r-process is a series of neutron capture reactions that synthesise many of the elements heavier than iron.) We identify line features in the spectra that are consistent with light r-process elements (atomic masses of 90-140). As it fades, the transient rapidly becomes red, and a higher-opacity, lanthanide-rich ejecta component may contribute to the emission. This indicates that neutron-star mergers produce gravitational waves and radioactively powered kilonovae, and are a nucleosynthetic source of the r-process elements.
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3.
  • Ackley, K., et al. (författare)
  • Observational constraints on the optical and near-infrared emission from the neutron star-black hole binary merger candidate S190814bv
  • 2020
  • Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 643
  • Tidskriftsartikel (refereegranskat)abstract
    • Context. Gravitational wave (GW) astronomy has rapidly reached maturity, becoming a fundamental observing window for modern astrophysics. The coalescences of a few tens of black hole (BH) binaries have been detected, while the number of events possibly including a neutron star (NS) is still limited to a few. On 2019 August 14, the LIGO and Virgo interferometers detected a high-significance event labelled S190814bv. A preliminary analysis of the GW data suggests that the event was likely due to the merger of a compact binary system formed by a BH and a NS.Aims. In this paper, we present our extensive search campaign aimed at uncovering the potential optical and near infrared electromagnetic counterpart of S190814bv. We found no convincing electromagnetic counterpart in our data. We therefore use our non-detection to place limits on the properties of the putative outflows that could have been produced by the binary during and after the merger.Methods. Thanks to the three-detector observation of S190814bv, and given the characteristics of the signal, the LIGO and Virgo Collaborations delivered a relatively narrow localisation in low latency - a 50% (90%) credible area of 5 deg(2) (23 deg(2)) - despite the relatively large distance of 26752 Mpc. ElectromagNetic counterparts of GRAvitational wave sources at the VEry Large Telescope collaboration members carried out an intensive multi-epoch, multi-instrument observational campaign to identify the possible optical and near infrared counterpart of the event. In addition, the ATLAS, GOTO, GRAWITA-VST, Pan-STARRS, and VINROUGE projects also carried out a search on this event. In this paper, we describe the combined observational campaign of these groups.Results. Our observations allow us to place limits on the presence of any counterpart and discuss the implications for the kilonova (KN), which was possibly generated by this NS-BH merger, and for the strategy of future searches. The typical depth of our wide-field observations, which cover most of the projected sky localisation probability (up to 99.8%, depending on the night and filter considered), is r similar to 22 (resp. K similar to 21) in the optical (resp. near infrared). We reach deeper limits in a subset of our galaxy-targeted observations, which cover a total similar to 50% of the galaxy-mass-weighted localisation probability. Altogether, our observations allow us to exclude a KN with large ejecta mass M greater than or similar to 0.1 M-circle dot to a high (> 90%) confidence, and we can exclude much smaller masses in a sub-sample of our observations. This disfavours the tidal disruption of the neutron star during the merger.Conclusions. Despite the sensitive instruments involved in the campaign, given the distance of S190814bv, we could not reach sufficiently deep limits to constrain a KN comparable in luminosity to AT 2017gfo on a large fraction of the localisation probability. This suggests that future (likely common) events at a few hundred megaparsecs will be detected only by large facilities with both a high sensitivity and large field of view. Galaxy-targeted observations can reach the needed depth over a relevant portion of the localisation probability with a smaller investment of resources, but the number of galaxies to be targeted in order to get a fairly complete coverage is large, even in the case of a localisation as good as that of this event.
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4.
  • Nicholl, M., et al. (författare)
  • Slowly fading super-luminous supernovae that are not pair-instability explosions
  • 2013
  • Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 502:7471, s. 346-
  • Tidskriftsartikel (refereegranskat)abstract
    • Super-luminous supernovae(1-4) that radiate more than 1044 ergs per second at their peak luminosity have recently been discovered in faint galaxies at redshifts of 0.1-4. Some evolve slowly, resembling models of 'pair-instability' supernovae(5,6). Such models involve stars with original masses 140-260 times that of the Sun that now have carbon-oxygen cores of 65-130 solar masses. In these stars, the photons that prevent gravitational collapse are converted to electron-positron pairs, causing rapid contraction and thermonuclear explosions. Many solar masses of Ni-56 are synthesized; this isotope decays to Fe-56 via Co-56, powering bright light curves(7,8). Such massive progenitors are expected to have formed from metal-poor gas in the early Universe(9). Recently, supernova 2007bi in a galaxy at redshift 0.127 (about 12 billion years after the Big Bang) with a metallicity one-third that of the Sun was observed to look like a fading pair-instability supernova(1,10). Here we report observations of two slow-to-fade super-luminous supernovae that show relatively fast rise times and blue colours, which are incompatible with pair-instability models. Their late-time light-curve and spectral similarities to supernova 2007bi call the nature of that event into question. Our early spectra closely resemble typical fast-declining super-luminous supernovae(2,11,12), which are not powered by radio-activity. Modelling our observations with 10-16 solar masses of magnetar-energized(13,14) ejecta demonstrates the possibility of a common explosion mechanism. The lack of unambiguous nearby pair-instability events suggests that their local rate of occurrence is less than 6 x 10(-6) times that of the core-collapse rate.
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5.
  • Chen, T.-W., et al. (författare)
  • SN 2017ens : The Metamorphosis of a Luminous Broadlined Type Ic Supernova into an SN IIn
  • 2018
  • Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8205 .- 2041-8213. ; 867:2
  • Tidskriftsartikel (refereegranskat)abstract
    • We present observations of supernova (SN) 2017ens, discovered by the ATLAS survey and identified as a hot blue object through the GREAT program. The redshift z = 0.1086 implies a peak brightness of M-g = -21.1 mag, placing the object within the regime of superluminous supernovae. We observe a dramatic spectral evolution, from initially being blue and featureless, to later developing features similar to those of the broadlined Type Ic SN 1998bw, and finally showing 2000 km s(-1) wide H alpha and H beta emission. Relatively narrow Balmer emission (reminiscent of a SN IIn) is present at all times. We also detect coronal lines, indicative of a dense circumstellar medium. We constrain the progenitor wind velocity to similar to 50-60 km s(-1) based on P-Cygni profiles, which is far slower than those present in Wolf-Rayet stars. This may suggest that the progenitor passed through a luminous blue variable phase, or that the wind is instead from a binary companion red supergiant star. At late times we see the similar to 2000 km s(-1) wide H alpha emission persisting at high luminosity (similar to 3 x 10(40) erg s(-1)) for at least 100 day, perhaps indicative of additional mass loss at high velocities that could have been ejected by a pulsational pair instability.
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6.
  • Gutierrez, C. P., et al. (författare)
  • DES16C3cje : A low-luminosity, long-lived supernova
  • 2020
  • Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 496:1, s. 95-110
  • Tidskriftsartikel (refereegranskat)abstract
    • We present DES16C3cje, a low-luminosity, long-lived type II supernova (SN II) at redshift 0.0618, detected by the Dark Energy Survey (DES). DES16C3cje is a unique SN. The spectra are characterized by extremely narrow photospheric lines corresponding to very low expansion velocities of less than or similar to 1500 km s(-1), and the light curve shows an initial peak that fades after 50 d before slowly rebrightening over a further 100 d to reach an absolute brightness of M-r similar to 15.5 mag. The decline rate of the late-time light curve is then slower than that expected from the powering by radioactive decay of Co-56, but is comparable to that expected from accretion power. Comparing the bolometric light curve with hydrodynamical models, we find that DES16C3cje can be explained by either (i) a low explosion energy (0.11 foe) and relatively large Ni-56 production of 0.075 M-circle dot from an similar to 15 M-circle dot red supergiant progenitor typical of other SNe II, or (ii) a relatively compact similar to 40 M-circle dot star, explosion energy of 1 foe, and 0.08 M-circle dot of Ni-56. Both scenarios require additional energy input to explain the late-time light curve, which is consistent with fallback accretion at a rate of similar to 0.5 x 10(-)(8) M-circle dot s(-1).
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7.
  • Pastorello, A., et al. (författare)
  • The evolution of luminous red nova AT 2017jfs in NGC 4470
  • 2019
  • Ingår i: Astronomy and Astrophysics. - : EDP SCIENCES S A. - 0004-6361 .- 1432-0746. ; 625
  • Tidskriftsartikel (refereegranskat)abstract
    • We present the results of our photometric and spectroscopic follow-up of the intermediate-luminosity optical transient AT 2017jfs. At peak, the object reaches an absolute magnitude of M-g = 15.46 +/- 0.15 mag and a bolometric luminosity of 5.5 x 10(41) erg s(-1). Its light curve has the double-peak shape typical of luminous red novae (LRNe), with a narrow first peak bright in the blue bands, while the second peak is longer-lasting and more luminous in the red and near-infrared (NIR) bands. During the first peak, the spectrum shows a blue continuum with narrow emission lines of H and Fe II. During the second peak, the spectrum becomes cooler, resembling that of a K-type star, and the emission lines are replaced by a forest of narrow lines in absorption. About 5 months later, while the optical light curves are characterized by a fast linear decline, the NIR ones show a moderate rebrightening, observed until the transient disappears in solar conjunction. At these late epochs, the spectrum becomes reminiscent of that of M-type stars, with prominent molecular absorption bands. The late-time properties suggest the formation of some dust in the expanding common envelope or an IR echo from foreground pre-existing dust. We propose that the object is a common-envelope transient, possibly the outcome of a merging event in a massive binary, similar to NGC4490-2011OT1.
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8.
  • Smartt, S. J., et al. (författare)
  • PESSTO : survey description and products from the first data release by the Public ESO Spectroscopic Survey of Transient Objects
  • 2015
  • Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 579
  • Tidskriftsartikel (refereegranskat)abstract
    • Context. The Public European Southern Observatory Spectroscopic Survey of Transient Objects (PESSTO) began as a public spectroscopic survey in April 2012. PESSTO classifies transients from publicly available sources and wide-field surveys, and selects science targets for detailed spectroscopic and photometric follow-up. PESSTO runs for nine months of the year, January - April and August - December inclusive, and typically has allocations of 10 nights per month. Aims. We describe the data reduction strategy and data products that are publicly available through the ESO archive as the Spectroscopic Survey data release 1 (SSDR1). Methods. PESSTO uses the New Technology Telescope with the instruments EFOSC2 and SOFI to provide optical and NIR spectroscopy and imaging. We target supernovae and optical transients brighter than 20.5(m) for classification. Science targets are selected for follow-up based on the PESSTO science goal of extending knowledge of the extremes of the supernova population. We use standard EFOSC2 set-ups providing spectra with resolutions of 13-18 angstrom between 3345-9995 angstrom. A subset of the brighter science targets are selected for SOFI spectroscopy with the blue and red grisms (0.935-2.53 mu m and resolutions 23-33 angstrom) and imaging with broadband JHK(s) filters. Results. This first data release (SSDR1) contains flux calibrated spectra from the first year (April 2012-2013). A total of 221 confirmed supernovae were classified, and we released calibrated optical spectra and classifications publicly within 24 h of the data being taken (via WISeREP). The data in SSDR1 replace those released spectra. They have more reliable and quantifiable flux calibrations, correction for telluric absorption, and are made available in standard ESO Phase 3 formats. We estimate the absolute accuracy of the flux calibrations for EFOSC2 across the whole survey in SSDR1 to be typically similar to 15%, although a number of spectra will have less reliable absolute flux calibration because of weather and slit losses. Acquisition images for each spectrum are available which, in principle, can allow the user to refine the absolute flux calibration. The standard NIR reduction process does not produce high accuracy absolute spectrophotometry but synthetic photometry with accompanying JHK(s) imaging can improve this. Whenever possible, reduced SOFI images are provided to allow this. Conclusions. Future data releases will focus on improving the automated flux calibration of the data products. The rapid turnaround between discovery and classification and access to reliable pipeline processed data products has allowed early science papers in the first few months of the survey.
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9.
  • Dall'Ora, M., et al. (författare)
  • THE TYPE IIP SUPERNOVA 2012aw IN M95 : HYDRODYNAMICAL MODELING OF THE PHOTOSPHERIC PHASE FROM ACCURATE SPECTROPHOTOMETRIC MONITORING
  • 2014
  • Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 787:2, s. 139-
  • Tidskriftsartikel (refereegranskat)abstract
    • We present an extensive optical and near-infrared photometric and spectroscopic campaign of the Type IIP supernova SN 2012aw. The data set densely covers the evolution of SN 2012aw shortly after the explosion through the end of the photospheric phase, with two additional photometric observations collected during the nebular phase, to fit the radioactive tail and estimate the Ni-56 mass. Also included in our analysis is the previously published Swift UV data, therefore providing a complete view of the ultraviolet-optical-infrared evolution of the photospheric phase. On the basis of our data set, we estimate all the relevant physical parameters of SN 2012aw with our radiation-hydrodynamics code: envelope mass M-env similar to 20 M-circle dot, progenitor radius R similar to 3 x 10(13) cm (similar to 430 R-circle dot), explosion energy E similar to 1.5 foe, and initial Ni-56 mass similar to 0.06 M-circle dot. These mass and radius values are reasonably well supported by independent evolutionary models of the progenitor, and may suggest a progenitor mass higher than the observational limit of 16.5 +/- 1.5 M-circle dot of the Type IIP events.
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10.
  • Pastorello, A., et al. (författare)
  • A luminous stellar outburst during a long-lasting eruptive phase first, and then SN IIn 2018cnf
  • 2019
  • Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 628
  • Tidskriftsartikel (refereegranskat)abstract
    • We present the results of the monitoring campaign of the Type IIn supernova (SN) 2018cnf (a.k.a. ASASSN-18mr). It was discovered about ten days before the maximum light (on MJD = 58 293.4 +/- 5.7 in the V band, with M-V = -18.13 +/- 0.15 mag). The multiband light curves show an immediate post-peak decline with some minor luminosity fluctuations, followed by a flattening starting about 40 days after maximum. The early spectra are relatively blue and show narrow Balmer lines with P Cygni profiles. Additionally, Fe II, O I, He I, and Ca II are detected. The spectra show little evolution with time and with intermediate-width features becoming progressively more prominent, indicating stronger interaction of the SN ejecta with the circumstellar medium. The inspection of archival images from the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) survey has revealed a variable source at the SN position with a brightest detection in December 2015 at M-r = -14.66 +/- 0.17 mag. This was likely an eruptive phase from the massive progenitor star that started from at least mid-2011, and that produced the circumstellar environment within which the star exploded as a Type IIn SN. The overall properties of SN 2018cnf closely resemble those of transients such as SN 2009ip. This similarity favours a massive hypergiant, perhaps a luminous blue variable, as progenitor for SN 2018cnf.
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11.
  • Smartt, S. J., et al. (författare)
  • Pan-STARRS and PESSTO search for an optical counterpart to the LIGO gravitational-wave source GW150914
  • 2016
  • Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 462:4, s. 4094-4116
  • Tidskriftsartikel (refereegranskat)abstract
    • We searched for an optical counterpart to the first gravitational-wave source discovered by LIGO (GW150914), using a combination of the Pan-STARRS1 wide-field telescope and the Public ESO Spectroscopic Survey of Transient Objects (PESSTO) spectroscopic follow-up programme. As the final LIGO sky maps changed during analysis, the total probability of the source being spatially coincident with our fields was finally only 4.2 per cent. Therefore, we discuss our results primarily as a demonstration of the survey capability of Pan-STARRS and spectroscopic capability of PESSTO. We mapped out 442 deg(2) of the northern sky region of the initial map. We discovered 56 astrophysical transients over a period of 41 d from the discovery of the source. Of these, 19 were spectroscopically classified and a further 13 have host galaxy redshifts. All transients appear to be fairly normal supernovae (SNe) and AGN variability and none is obviously linked with GW150914. We illustrate the sensitivity of our survey by defining parametrized light curves with time-scales of 4, 20 and 40 d and use the sensitivity of the Pan-STARRS1 images to set limits on the luminosities of possible sources. The Pan-STARRS1 images reach limiting magnitudes of iP1 = 19.2, 20.0 and 20.8, respectively, for the three time-scales. For long time-scale parametrized light curves (with full width half-maximum similar or equal to 40 d), we set upper limits of M-i <= -17.2(+1.4)(-0.9) if the distance to GW150914 is D-L = 400 +/- 200 Mpc. The number of Type Ia SN we find in the survey is similar to that expected from the cosmic SN rate, indicating a reasonably complete efficiency in recovering SN like transients out to D-L = 400 +/- 200 Mpc.
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12.
  • Anderson, J. P., et al. (författare)
  • A nearby super-luminous supernova with a long pre-maximum plateau and strong C (II) features
  • 2018
  • Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 620
  • Tidskriftsartikel (refereegranskat)abstract
    • Context. Super-luminous supernovae (SLSNe) are rare events defined as being significantly more luminous than normal terminal stellar explosions. The source of the additional power needed to achieve such luminosities is still unclear. Discoveries in the local Universe (i.e. z < 0.1) are scarce, but afford dense multi-wavelength observations. Additional low-redshift objects are therefore extremely valuable.Aims. We present early-time observations of the type I SLSN ASASSN-18km/SN 2018bsz. These data are used to characterise the event and compare to literature SLSNe and spectral models. Host galaxy properties are also analysed.Methods. Optical and near-IR photometry and spectroscopy were analysed. Early-time ATLAS photometry was used to constrain the rising light curve. We identified a number of spectral features in optical-wavelength spectra and track their time evolution. Finally, we used archival host galaxy photometry together with H( II )region spectra to constrain the host environment.Results. ASASSN-18km/SN 2018bsz is found to be a type I SLSN in a galaxy at a redshift of 0.0267 (111 Mpc), making it the lowest-redshift event discovered to date. Strong C- II lines are identified in the spectra. Spectral models produced by exploding a Wolf-Rayet progenitor and injecting a magnetar power source are shown to be qualitatively similar to ASASSN-18km/SN 2018bsz, contrary to most SLSNe-I that display weak or non-existent C (II) lines. ASASSN-18km/SN 2018bsz displays along, slowly rising, red plateau of >26 days, before a steeper, faster rise to maximum. The host has an absolute magnitude of -19.8 mag (r), a mass of M-* = 1.5(-0.33)(+0.08) x 10(9) M-circle dot, and a star formation rate of =0.50(-0.19)(+2.22) M-circle dot yr(-1). A nearby H (II) region has an oxygen abundance (O3N2) of 8.31 +/- 0.01 dex.
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13.
  • Cai, Y.-Z., et al. (författare)
  • Intermediate-luminosity red transients : Spectrophotometric properties and connection to electron-capture supernova explosions
  • 2021
  • Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 654
  • Tidskriftsartikel (refereegranskat)abstract
    • We present the spectroscopic and photometric study of five intermediate-luminosity red transients (ILRTs), namely AT 2010dn, AT 2012jc, AT 2013la, AT 2013lb, and AT 2018aes. They share common observational properties and belong to a family of objects similar to the prototypical ILRT SN 2008S. These events have a rise time that is less than 15 days and absolute peak magnitudes of between −11.5 and −14.5 mag. Their pseudo-bolometric light curves peak in the range 0.5–9.0 × 1040 erg s−1 and their total radiated energies are on the order of (0.3–3) × 1047 erg. After maximum brightness, the light curves show a monotonic decline or a plateau, resembling those of faint supernovae IIL or IIP, respectively. At late phases, the light curves flatten, roughly following the slope of the 56Co decay. If the late-time power source is indeed radioactive decay, these transients produce 56Ni masses on the order of 10−4 to 10−3 M⊙. The spectral energy distribution of our ILRT sample, extending from the optical to the mid-infrared (MIR) domain, reveals a clear IR excess soon after explosion and non-negligible MIR emission at very late phases. The spectra show prominent H lines in emission with a typical velocity of a few hundred km s−1, along with Ca II features. In particular, the [Ca II] λ7291,7324 doublet is visible at all times, which is a characteristic feature for this family of transients. The identified progenitor of SN 2008S, which is luminous in archival Spitzer MIR images, suggests an intermediate-mass precursor star embedded in a dusty cocoon. We propose the explosion of a super-asymptotic giant branch star forming an electron-capture supernova as a plausible explanation for these events.
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14.
  • Prentice, S. J., et al. (författare)
  • Investigating the properties of stripped-envelope supernovae; what are the implications for their progenitors?
  • 2019
  • Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 485:2, s. 1559-1578
  • Tidskriftsartikel (refereegranskat)abstract
    • We present observations and analysis of 18 stripped-envelope supernovae observed during 2013-2018. This sample consists of five H/He-rich SNe, sixH-poor/He-rich SNe, three narrow lined SNe Ic, and four broad lined SNe Ic. The peak luminosity and characteristic time-scales of the bolometric light curves are calculated, and the light curves modelled to derive Ni-56 and ejecta masses (M-Ni and M-cj). Additionally, the temperature evolution and spectral line velocity curves of each SN are examined. Analysis of the [O I] line in the nebular phase of eight SNe suggests their progenitors had initial masses < 20 M-circle dot. The bolometric light curve properties are examined in combination with those of other SE events from the literature. The resulting data set gives the M-ej distribution for 80 SE-SNe, the largest such sample in the literature to date, and shows that SNe Ib have the lowest median M-ej, followed by narrow-lined SNe Ic, H/He-rich SNe, broad-lined SNe Ic, and finally gamma-ray burst SNe. SNe Ic-6/7 show the largest spread of M-ej ranging from similar to 1.2-11 M-circle dot, considerably greater than any other subtype. For all SE-SNe = 2.8 +/- 1.5 M-circle dot which further strengthens the evidence that SE-SNe arise from low-mass progenitors which are typically <5 M-circle dot at the time of explosion, again suggesting M-ZAMS < 25 M-circle dot. The low and lack of clear bimodality in the distribution implies < 30 M-circle dot progenitors and that envelope stripping via binary interaction is the dominant evolutionary pathway of these SNe.
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15.
  • Smartt, S. J., et al. (författare)
  • A SEARCH FOR AN OPTICAL COUNTERPART TO THE GRAVITATIONAL-WAVE EVENT GW151226
  • 2016
  • Ingår i: Astrophysical Journal Letters. - 2041-8205 .- 2041-8213. ; 827:2
  • Tidskriftsartikel (refereegranskat)abstract
    • We present a search for an electromagnetic counterpart of the gravitational-wave source GW151226. Using the Pan-STARRS1 telescope we mapped out 290 square degrees in the optical i(P1) filter, starting 11.5 hr after the LIGO information release and lasting for an additional 28 days. The first observations started 49.5 hr after the time of the GW151226 detection. We typically reached sensitivity limits of i(P1) = 20.3-20.8 and covered 26.5% of the LIGO probability skymap. We supplemented this with ATLAS survey data, reaching 31% of the probability region to shallower depths of m similar or equal to 19. We found 49 extragalactic transients (that are not obviously active galactic nuclei), including a faint transient in a galaxy at 7 Mpc (a luminous blue variable outburst) plus a rapidly decaying M-dwarf flare. Spectral classification of 20 other transient events showed them all to be supernovae. We found an unusual transient, PS15dpn, with an explosion date temporally coincident with GW151226, that evolved into a type Ibn supernova. The redshift of the transient is secure at z = 0.1747 +/- 0.0001 and we find it unlikely to be linked, since the luminosity distance has a negligible probability of being consistent with that of GW151226. In the 290 square degrees surveyed we therefore do not find a likely counterpart. However we show that our survey strategy would be sensitive to NS-NS mergers producing kilonovae at D-L less than or similar to 100 Mpc, which is promising for future LIGO/Virgo searches.
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16.
  • Valenti, S., et al. (författare)
  • PESSTO spectroscopic classification of La Silla-Quest Transients
  • 2012
  • Rapport (övrigt vetenskapligt/konstnärligt)abstract
    • PESSTO is the "Public ESO Spectroscopic Survey of Transient Objects" (http://www.pessto.org) using the ESO New Technology Telescope (NTT) at La Silla and the EFOSC2 (optical) and SOFI (near-IR) spectrographs. It is one of two currently running public spectroscopic surveys at ESO. The survey details are as follows: - PESSTO has 90 nights per year on the NTT: 9 lunations (August to April), 10 nights per lunation (we are not observing May-July).
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17.
  • Andrews, Jennifer E., et al. (författare)
  • SN 2017gmr : An Energetic Type II-P Supernova with Asymmetries
  • 2019
  • Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 885:1
  • Tidskriftsartikel (refereegranskat)abstract
    • We present high-cadence UV, optical, and near-infrared data on the luminous Type II-P supernova SN;2017gmr from hours after discovery through the first 180 days. SN;2017gmr does not show signs of narrow, high-ionization emission lines in the early optical spectra, yet the optical light-curve evolution suggests that an extra energy source from circumstellar medium (CSM) interaction must be present for at least 2 days after explosion. Modeling of the early light curve indicates a ?500 R progenitor radius, consistent with a rather compact red supergiant, and late-time luminosities indicate that up to 0.130;;0.026 M of Ni-56 are present, if the light curve is solely powered by radioactive decay, although the Ni-56 mass may be lower if CSM interaction contributes to the post-plateau luminosity. Prominent multipeaked emission lines of H? and [O i] emerge after day 154, as a result of either an asymmetric explosion or asymmetries in the CSM. The lack of narrow lines within the first 2 days of explosion in the likely presence of CSM interaction may be an example of close, dense, asymmetric CSM that is quickly enveloped by the spherical supernova ejecta.
  •  
18.
  • Brennan, S. J., et al. (författare)
  • Photometric and spectroscopic evolution of the interacting transient AT 2016jbu(Gaia16cfr)
  • 2022
  • Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 513:4, s. 5642-5665
  • Tidskriftsartikel (refereegranskat)abstract
    • We present the results from a high-cadence, multiwavelength observation campaign of AT 2016jbu (aka Gaia16cfr), an interacting transient. This data set complements the current literature by adding higher cadence as well as extended coverage of the light-curve evolution and late-time spectroscopic evolution. Photometric coverage reveals that AT 2016jbu underwent significant photometric variability followed by two luminous events, the latter of which reached an absolute magnitude of MV ∼ −18.5 mag. This is similar to the transient SN 2009ip whose nature is still debated. Spectra are dominated by narrow emission lines and show a blue continuum during the peak of the second event. AT 2016jbu shows signatures of a complex, non-homogeneous circumstellar material (CSM). We see slowly evolving asymmetric hydrogen line profiles, with velocities of 500 km s−1 seen in narrow emission features from a slow-moving CSM, and up to 10 000 km s−1 seen in broad absorption from some high-velocity material. Late-time spectra (∼+1 yr) show a lack of forbidden emission lines expected from a core-collapse supernova and are dominated by strong emission from H, He I, and Ca II. Strong asymmetric emission features, a bumpy light curve, and continually evolving spectra suggest an inhibit nebular phase. We compare the evolution of H α among SN 2009ip-like transients and find possible evidence for orientation angle effects. The light-curve evolution of AT 2016jbu suggests similar, but not identical, circumstellar environments to other SN 2009ip-like transients.
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19.
  • Brennan, S. J., et al. (författare)
  • Progenitor, environment, and modelling of the interacting transient AT 2016jbu (Gaia16cfr)
  • 2022
  • Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 513:4, s. 5666-5685
  • Tidskriftsartikel (refereegranskat)abstract
    • We present the bolometric light curve, identification and analysis of the progenitor candidate, and preliminary modelling of AT 2016jbu (Gaia16cfr). We find a progenitor consistent with a ∼ 22–25 M⊙ yellow hypergiant surrounded by a dusty circumstellar shell, in agreement with what has been previously reported. We see evidence for significant photometric variability in the progenitor, as well as strong Hα emission consistent with pre-existing circumstellar material. The age of the environment, as well as the resolved stellar population surrounding AT 2016jbu, supports a progenitor age of >10 Myr, consistent with a progenitor mass of ∼22 M⊙. A joint analysis of the velocity evolution of AT 2016jbu and the photospheric radius inferred from the bolometric light curve shows the transient is consistent with two successive outbursts/explosions. The first outburst ejected material with velocity ∼650 km s−1, while the second, more energetic event ejected material at ∼4500 km s−1. Whether the latter is the core collapse of the progenitor remains uncertain. We place a limit on the ejected 56Ni mass of <0.016 M⊙. Using the Binary Population And Spectral Synthesis (BPASS) code, we explore a wide range of possible progenitor systems and find that the majority of these are in binaries, some of which are undergoing mass transfer or common-envelope evolution immediately prior to explosion. Finally, we use the SuperNova Explosion Code (SNEC) to demonstrate that the low-energy explosions within some of these binary systems, together with sufficient circumstellar material, can reproduce the overall morphology of the light curve of AT 2016jbu.
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20.
  • Gromadzki, M., et al. (författare)
  • Discovery and follow-up of the unusual nuclear transient OGLE17aaj
  • 2019
  • Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 622
  • Tidskriftsartikel (refereegranskat)abstract
    • Aims. We report on the discovery and follow-up of a peculiar transient, OGLE17aaj, which occurred in the nucleus of a weakly active galaxy. We investigate whether it can be interpreted as a new candidate for a tidal disruption event (TDE).Methods. We present the OGLE-IV light curve that covers the slow 60-day-long rise to maximum along with photometric, spectro-scopic, and X-ray follow-up during the first year.Results. OGLE17aaj is a nuclear transient exhibiting some properties similar to previously found TDEs, including a long rise time, lack of colour-temperature evolution, and high black-body temperature. On the other hand, its narrow emission lines and slow post-peak evolution are different from previously observed TDEs. Its spectrum and light-curve evolution is similar to F01004-2237 and AT 2017bgt. Signatures of historical low-level nuclear variability suggest that OGLE17aaj may instead be related to a new type of accretion event in active super-massive black holes.
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21.
  • Leloudas, G., et al. (författare)
  • The superluminous transient ASASSN-15lh as a tidal disruption event from a Kerr black hole
  • 2016
  • Ingår i: Nature Astronomy. - : Springer Science and Business Media LLC. - 2397-3366. ; 1:1
  • Tidskriftsartikel (refereegranskat)abstract
    • When a star passes within the tidal radius of a supermassive black hole, it will be torn apart1. For a star with the mass of the Sun (M-circle dot) and a non-spinning black hole with a mass <10(8)M(circle dot), the tidal radius lies outside the black hole event horizon2 and the disruption results in a luminous flare(3-6). Here we report observations over a period of ten months of a transient, hitherto interpreted(7) as a superluminous supernova(8). Our data show that the transient rebrightened substantially in the ultraviolet and that the spectrum went through three different spectroscopic phases without ever becoming nebular. Our observations are more consistent with a tidal disruption event than a superluminous supernova because of the temperature evolution(6), the presence of highly ionized CNO gas in the line of sight(9) and our improved localization of the transient in the nucleus of a passive galaxy, where the presence of massive stars is highly unlikely(10,11). While the supermassive black hole has a mass >10(8)M(circle dot)(12,13), a star with the same mass as the Sun could be disrupted outside the event horizon if the black hole were spinning rapidly(14). The rapid spin and high black hole mass can explain the high luminosity of this event.
  •  
22.
  • Melandri, A., et al. (författare)
  • GRB171010A/SN 2017htp : a GRB-SN at z=0.33
  • 2019
  • Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 490:4, s. 5366-5374
  • Tidskriftsartikel (refereegranskat)abstract
    • The number of supernovae known to be connected with long-duration gamma-ray bursts (GRBs) is increasing and the link between these events is no longer exclusively found at low redshift (z less than or similar to 0.3) but is well established also at larger distances. We present a new case of such a liaison at z = 0.33 between GRB171010A and SN 2017htp. It is the second closest GRB with an associated supernova of only three events detected by Fermi-LAT. The supernova is one of the few higher redshift cases where spectroscopic observations were possible and shows spectral similarities with the well-studied SN 1998bw, having produced a similar Ni mass (M-Ni = 0.33 +/- 0.02 M-circle dot) with slightly lower ejected mass (M-ej = 4.1 +/- 0.7 M-circle dot) and kinetic energy (E-K = 8.1 +/- 2.5 x 10(51) erg). The host-galaxy is bigger in size than typical GRB host galaxies, but the analysis of the region hosting the GRB revealed spectral properties typically observed in GRB hosts and showed that the progenitor of this event was located in a very bright H II region of its face-on host galaxy, at a projected distance of similar to 10 kpc from its galactic centre. The star-formation rate (SFRGRB similar to 0.2 M-circle dot yr(-1)) and metallicity (12 + log(O/H) similar to 8.15 +/- 0.10) of the GRB star-forming region are consistent with those of the host galaxies of previously studied GRB-SN systems.
  •  
23.
  • Nicholl, M., et al. (författare)
  • Superluminous supernovae from PESSTO
  • 2014
  • Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 444:3, s. 2096-2113
  • Tidskriftsartikel (refereegranskat)abstract
    • We present optical spectra and light curves for three hydrogen-poor superluminous supernovae followed by the Public ESO Spectroscopic Survey of Transient Objects (PESSTO). Time series spectroscopy from a fewdays aftermaximum light to 100 d later shows them to be fairly typical of this class, with spectra dominated by Ca II, MgII, FeII, and Si II, which evolve slowly over most of the post-peak photospheric phase. We determine bolometric light curves and apply simple fitting tools, based on the diffusion of energy input by magnetar spin-down, Ni-56 decay, and collision of the ejecta with an opaque circumstellar shell. We investigate how the heterogeneous light curves of our sample (combined with others from the literature) can help to constrain the possible mechanisms behind these events. We have followed these events to beyond 100-200 d after peak, to disentangle host galaxy light from fading supernova flux and to differentiate between the models, which predict diverse behaviour at this phase. Models powered by radioactivity require unrealistic parameters to reproduce the observed light curves, as found by previous studies. Both magnetar heating and circumstellar interaction still appear to be viable candidates. A large diversity is emerging in observed tail-phase luminosities, with magnetar models failing in some cases to predict the rapid drop in flux. This would suggest either that magnetars are not responsible, or that the X-ray flux from the magnetar wind is not fully trapped. The light curve of one object shows a distinct rebrightening at around 100 d after maximum light. We argue that this could result either from multiple shells of circumstellar material, or from a magnetar ionization front breaking out of the ejecta.
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24.
  • Tartaglia, L., et al. (författare)
  • The Early Detection and Follow-up of the Highly Obscured Type II Supernova 2016ija/DLT16am
  • 2018
  • Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 853:1
  • Tidskriftsartikel (refereegranskat)abstract
    • We present our analysis of the Type II supernova DLT16am (SN 2016ija). The object was discovered during the ongoing D < 40 Mpc (DLT40) one-day cadence supernova search at r similar to 20.1 mag in the edge-on nearby (D = 20.0 +/- 4.0 Mpc) galaxy NGC 1532. The subsequent prompt and high-cadenced spectroscopic and photometric follow-up revealed a highly extinguished transient, with E(B - V) = 1.95 +/- 0.15 mag, consistent with a standard extinction law with R-V = 3.1 and a bright (M-V = -18.48 +/- 0.77 mag) absolute peak magnitude. A comparison of the photometric features with those of large samples of SNe II reveals a fast rise for the derived luminosity and a relatively short plateau phase, with a slope of S-50V = 0.84 +/- 0.04 mag/50 days, consistent with the photometric properties typical of those of fast-declining SNe II. Despite the large uncertainties on the distance and the extinction in the direction of DLT16am, the measured photospheric expansion velocity and the derived absolute V-band magnitude at similar to 50 days after the explosion match the existing luminosity-velocity relation for SNe II.
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25.
  • Yuan, Fang, et al. (författare)
  • 450 d of Type II SN 2013ej in optical and near-infrared
  • 2016
  • Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 461:2, s. 2003-2018
  • Tidskriftsartikel (refereegranskat)abstract
    • We present optical and near-infrared photometric and spectroscopic observations of SN 2013ej, in galaxy M74, from 1 to 450 d after the explosion. SN 2013ej is a hydrogen-rich supernova, classified as a Type IIL due to its relatively fast decline following the initial peak. It has a relatively high peak luminosity (absolute magnitude M-V =-17.6) but a small 56Ni production of similar to 0.023 M-circle dot. Its photospheric evolution is similar to other Type II SNe, with shallow absorption in the H a profile typical for a Type IIL. During transition to the radioactive decay tail at similar to 100 d, we find the SN to grow bluer in B - V colour, in contrast to some other Type II supernovae. At late times, the bolometric light curve declined faster than expected from Co-56 decay and we observed unusually broad and asymmetric nebular emission lines. Based on comparison of nebular emission lines most sensitive to the progenitor core mass, we find our observations are best matched to synthesized spectral models with a M-ZAMS = 12-15 M-circle dot progenitor. The derived mass range is similar to but not higher than the mass estimated for Type IIP progenitors. This is against the idea that Type IIL are from more massive stars. Observations are consistent with the SN having a progenitor with a relatively low-mass envelope.
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26.
  • Barbarino, C., et al. (författare)
  • SN 2012ec : mass of the progenitor from PESSTO follow-up of the photospheric phase
  • 2015
  • Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 448:3, s. 2312-2331
  • Tidskriftsartikel (refereegranskat)abstract
    • We present the results of a photometric and spectroscopic monitoring campaign of SN 2012ec, which exploded in the spiral galaxy NGC 1084, during the photospheric phase. The photometric light curve exhibits a plateau with luminosity L = 0.9 x 10(42) erg s(-1) and duration similar to 90 d, which is somewhat shorter than standard Type II-P supernovae (SNe). We estimate the nickel mass M(Ni-56) = 0.040 +/- 0.015 M-circle dot from the luminosity at the beginning of the radioactive tail of the light curve. The explosion parameters of SN 2012ec were estimated from the comparison of the bolometric light curve and the observed temperature and velocity evolution of the ejecta with predictions from hydrodynamical models. We derived an envelope mass of 12.6 M-circle dot, an initial progenitor radius of 1.6 x 10(13) cm and an explosion energy of 1.2 foe. These estimates agree with an independent study of the progenitor star identified in pre-explosion images, for which an initial mass of M = 14-22 M-circle dot was determined. We have applied the same analysis to two other Type II-P SNe (SNe 2012aw and 2012A), and carried out a comparison with the properties of SN 2012ec derived in this paper. We find a reasonable agreement between the masses of the progenitors obtained from pre-explosion images and masses derived from hydrodynamical models. We estimate the distance to SN 2012ec with the standardized candle method (SCM) and compare it with other estimates based on other primary and secondary indicators. SNe 2012A, 2012aw and 2012ec all follow the standard relations for the SCM for the use of Type II-P SNe as distance indicators.
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27.
  • Benetti, S., et al. (författare)
  • The supernova CSS121015:004244+132827 : a clue for understanding superluminous supernovae
  • 2014
  • Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 441:1, s. 289-303
  • Tidskriftsartikel (refereegranskat)abstract
    • We present optical photometry and spectra of the superluminous Type II/IIn supernova (SN) CSS121015: 004244+132827 (z = 0.2868) spanning epochs from -30 d (rest frame) to more than 200 d after maximum. CSS121015 is one of the more luminous SNe ever found and one of the best observed. The photometric evolution is characterized by a relatively fast rise to maximum (similar to 40 d in the SN rest frame), and by a linear post-maximum decline. The light curve shows no sign of a break to an exponential tail. A broad Ha is first detected at similar to+40 d (rest frame). Narrow, barely resolved Balmer and [O III] 5007 angstrom lines, with decreasing strength, are visible along the entire spectral evolution. The spectra are very similar to other superluminous supernovae (SLSNe) with hydrogen in their spectrum, and also to SN 2005gj, sometimes considered Type Ia interacting with H-rich circumstellar medium. The spectra are also similar to a subsample of H-deficient SLSNe. We propose that the properties of CSS121015 are consistent with the interaction of the ejecta with a massive, extended, opaque shell, lost by the progenitor decades before the final explosion, although a magnetar-powered model cannot be excluded. Based on the similarity of CSS121015 with other SLSNe (with and without H), we suggest that the shocked-shell scenario should be seriously considered as a plausible model for both types of SLSN.
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28.
  •  
29.
  • Childress, M. J., et al. (författare)
  • Measuring nickel masses in Type Ia supernovae using cobalt emission in nebular phase spectra
  • 2015
  • Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 454:4, s. 3816-3842
  • Tidskriftsartikel (refereegranskat)abstract
    • The light curves of Type Ia supernovae (SNe Ia) are powered by the radioactive decay of Ni-56 to Co-56 at early times, and the decay of Co-56 to Fe-56 from similar to 60 d after explosion. We examine the evolution of the [Co III] lambda 5893 emission complex during the nebular phase for SNe Ia with multiple nebular spectra and show that the line flux follows the square of the mass of Co-56 as a function of time. This result indicates both efficient local energy deposition from positrons produced in Co-56 decay and long-term stability of the ionization state of the nebula. We compile SN Ia nebular spectra from the literature and present 21 new late-phase spectra of 7 SNe Ia, including SN 2014J. From these we measure the flux in the [Co III] lambda 5893 line and remove its well-behaved time dependence to infer the initial mass of Ni-56 (M-Ni, produced in the explosion. We then examine Ni-56 yields for different SN Ia ejected masses (M-ej-calculated using the relation between light-curve width and ejected mass) and find that the Ni-56 masses of SNe Ia fall into two regimes: for narrow light curves (low stretch s similar to 0.7-0.9), M-Ni is clustered near MN, 0.4 Me and shows a shallow increase as Mei increases from similar to 1 to 1.4 M-circle dot; at high stretch, M-ej clusters at the Chandrasekhar mass (1.4 M-circle dot) while M-Ni, spans a broad range from 0.6 to 1.2 M-circle dot. This could constitute evidence for two distinct SN Ia explosion mechanisms.
  •  
30.
  • Inserra, C., et al. (författare)
  • OGLE-2013-SN-079 : A LONELY SUPERNOVA CONSISTENT WITH A HELIUM SHELL DETONATION
  • 2015
  • Ingår i: Astrophysical Journal Letters. - 2041-8205 .- 2041-8213. ; 799:1
  • Tidskriftsartikel (refereegranskat)abstract
    • We present observational data for a peculiar supernova discovered by the OGLE-IV survey and followed by the Public ESO Spectroscopic Survey for Transient Objects. The inferred redshift of z = 0.07 implies an absolute magnitude in the rest-frame I-band of M-1 similar to -17.6 mag. This places it in the luminosity range between normal Type Ia SNe and novae. Optical and near infrared spectroscopy reveal mostly Ti and Ca lines, and an unusually red color arising from strong depression of flux at rest wavelengths <5000 angstrom. To date, this is the only reported SN showing Ti-dominated spectra. The data are broadly consistent with existing models for the pure detonation of a helium shell around a low-mass CO white dwarf and double-detonation models that include a secondary detonation of a CO core following a primary detonation in an overlying helium shell.
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31.
  • Kankare, E., et al. (författare)
  • Core-collapse supernova subtypes in luminous infrared galaxies
  • 2021
  • Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 649
  • Tidskriftsartikel (refereegranskat)abstract
    • The fraction of core-collapse supernovae (CCSNe) occurring in the central regions of galaxies is not well constrained at present. This is partly because large-scale transient surveys operate at optical wavelengths, making it challenging to detect transient sources that occur in regions susceptible to high extinction factors. Here we present the discovery and follow-up observations of two CCSNe that occurred in the luminous infrared galaxy (LIRG) NGC 3256. The first, SN 2018ec, was discovered using the ESO HAWK-I /GRAAL adaptive optics seeing enhancer, and was classified as a Type Ic with a host galaxy extinction of AV = 2:1+0:3 0:1 mag. The second, AT 2018cux, was discovered during the course of follow-up observations of SN 2018ec, and is consistent with a subluminous Type IIP classification with an AV = 2:1 +/- 0:4 mag of host extinction. A third CCSN, PSN J10275082 4354034 in NGC 3256, was previously reported in 2014, and we recovered the source in late-time archival Hubble Space Telescope imaging. Based on template light curve fitting, we favour a Type IIn classification for it with modest host galaxy extinction of AV = 0:3+0:4 0:3 mag. We also extend our study with follow-up data of the recent Type IIb SN 2019lqo and Type Ib SN 2020fkb that occurred in the LIRG system Arp 299 with host extinctions of AV = 2:1 +0:1 0 :3 and AV = 0:4 +0:1 0 :2 mag, respectively. Motivated by the above, we inspected, for the first time, a sample of 29 CCSNe located within a projected distance of 2.5 kpc from the host galaxy nuclei in a sample of 16 LIRGs. We find, if star formation within these galaxies is modelled assuming a global starburst episode and normal IMF, that there is evidence of a correlation between the starburst age and the CCSN subtype. We infer that the two subgroups of 14 H-poor (Type IIb /Ib /Ic /Ibn) and 15 H-rich (Type II /IIn) CCSNe have di fferent underlying progenitor age distributions, with the H-poor progenitors being younger at 3 sigma significance. However, we note that the currently available sample sizes of CCSNe and host LIRGs are small, and the statistical comparisons between subgroups do not take into account possible systematic or model errors related to the estimated starburst ages.
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32.
  • Maguire, K., et al. (författare)
  • A statistical analysis of circumstellar material in Type Ia supernovae
  • 2013
  • Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 436:1, s. 222-240
  • Tidskriftsartikel (refereegranskat)abstract
    • A key tracer of the elusive progenitor systems of Type Ia supernovae (SNe Ia) is the detection of narrow blueshifted time-varying Na I D absorption lines, interpreted as evidence of circumstellar material surrounding the progenitor system. The origin of this material is controversial, but the simplest explanation is that it results from previous mass-loss in a system containing a white dwarf and a non-degenerate companion star. We present new single-epoch intermediate-resolution spectra of 17 low-redshift SNe Ia taken with XShooter on the European Southern Observatory Very Large Telescope. Combining this sample with events from the literature, we confirm an excess (similar to 20 per cent) of SNe Ia displaying blueshifted narrow Na I D absorption features compared to redshifted Na I D features. The host galaxies of SNe Ia displaying blueshifted absorption profiles are skewed towards later-type galaxies, compared to SNe Ia that show no Na I D absorption and SNe Ia displaying blueshifted narrow Na I D absorption features have broader light curves. The strength of the Na I D absorption is stronger in SNe Ia displaying blueshifted Na I D absorption features than those without blueshifted features, and the strength of the blueshifted Na I D is correlated with the B - V colour of the SN at maximum light. This strongly suggests the absorbing material is local to the SN. In the context of the progenitor systems of SNe Ia, we discuss the significance of these findings and other recent observational evidence on the nature of SN Ia progenitors. We present a summary that suggests that there are at least two distinct populations of normal, cosmologically useful SNe Ia.
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33.
  • Medler, K., et al. (författare)
  • SN 2020acat : an energetic fast rising Type IIb supernova
  • 2022
  • Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 513:4, s. 5540-5558
  • Tidskriftsartikel (refereegranskat)abstract
    • The ultraviolet (UV) and near-infrared (NIR) photometric and optical spectroscopic observations of SN 2020acat covering ∼250 d after explosion are presented here. Using the fast rising photometric observations, spanning from the UV to NIR wavelengths, a pseudo-bolometric light curve was constructed and compared to several other well-observed Type IIb supernovae (SNe IIb). SN 2020acat displayed a very short rise time reaching a peak luminosity of Log10(L)=42.49±0.17ergs−1 in only ∼14.6 ± 0.3 d. From modelling of the pseudo-bolometric light curve, we estimated a total mass of 56Ni synthesized by SN 2020acat of MNi = 0.13 ± 0.03 M⊙, with an ejecta mass of Mej = 2.3 ± 0.4 M⊙ and a kinetic energy of Ek = 1.2 ± 0.3 × 1051 erg. The optical spectra of SN 2020acat display hydrogen signatures well into the transitional period (≳ 100 d), between the photospheric and the nebular phases. The spectra also display a strong feature around 4900  Å that cannot be solely accounted for by the presence of the Fe II 5018 line. We suggest that the Fe II feature was augmented by He I 5016 and possibly by the presence of N II 5005. From both photometric and spectroscopic analysis, we inferred that the progenitor of SN 2020acat was an intermediate-mass compact star with an MZAMS of 15–20 M⊙.
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34.
  • Pastorello, A., et al. (författare)
  • Luminous red novae : Stellar mergers or giant eruptions?
  • 2019
  • Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 630
  • Tidskriftsartikel (refereegranskat)abstract
    • We present extensive datasets for a class of intermediate-luminosity optical transients known as luminous red novae. They show double-peaked light curves, with an initial rapid luminosity rise to a blue peak (at -13 to -15 mag), which is followed by a longer-duration red peak that sometimes is attenuated, resembling a plateau. The progenitors of three of them (NGC 4490-2011OT1, M 101-2015OT1, and SNhunt248), likely relatively massive blue to yellow stars, were also observed in a pre-eruptive stage when their luminosity was slowly increasing. Early spectra obtained during the first peak show a blue continuum with superposed prominent narrow Balmer lines, with P Cygni profiles. Lines of Fe II are also clearly observed, mostly in emission. During the second peak, the spectral continuum becomes much redder, H alpha is barely detected, and a forest of narrow metal lines is observed in absorption. Very late-time spectra (similar to 6 months after blue peak) show an extremely red spectral continuum, peaking in the infrared (IR) domain. H alpha is detected in pure emission at such late phases, along with broad absorption bands due to molecular overtones (such as TiO, VO). We discuss a few alternative scenarios for luminous red novae. Although major instabilities of single massive stars cannot be definitely ruled out, we favour a common envelope ejection in a close binary system, with possibly a final coalescence of the two stars. The similarity between luminous red novae and the outburst observed a few months before the explosion of the Type IIn SN 2011ht is also discussed.
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35.
  • Terreran, G., et al. (författare)
  • Hydrogen-rich supernovae beyond the neutrino-driven core-collapse paradigm
  • 2017
  • Ingår i: Nature Astronomy. - : Springer Science and Business Media LLC. - 2397-3366. ; 1:10, s. 713-720
  • Tidskriftsartikel (refereegranskat)abstract
    • Type II supernovae are the final stage of massive stars (above 8 M-circle dot) which retain part of their hydrogen-rich envelope at the moment of explosion. They typically eject up to 15 M-circle dot of material, with peak magnitudes of -17.5 mag and energies in the order of 10(51) erg, which can be explained by neutrino-driven explosions and neutron star formation. Here, we present our study of OGLE-2014-SN-073, one of the brightest type II supernovae ever discovered, with an unusually broad lightcurve combined with high ejecta velocities. From our hydrodynamical modelling, we infer a remarkable ejecta mass of 60(-16)(+42) M-circle dot and a relatively high explosion energy of 12.4(-5.9)(+13.0) x 10(51) erg. We show that this object belongs, along with a very small number of other hydrogen-rich supernovae, to an energy regime that is not explained by standard core-collapse neutrino-driven explosions. We compare the quantities inferred by the hydrodynamical modelling with the expectations of various exploding scenarios and attempt to explain the high energy and luminosity released. We find some qualitative similarities with pair-instability supernovae, although the prompt injection of energy by a magnetar seems to be a viable alternative explanation for such an extreme event.
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36.
  • Fiore, A., et al. (författare)
  • SN 2017gci : a nearby Type I Superluminous Supernova with a bumpy tail
  • 2021
  • Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 502:2, s. 2120-2139
  • Tidskriftsartikel (refereegranskat)abstract
    • We present and discuss the optical spectrophotometric observations of the nearby (z = 0.087) Type I superluminous supernova (SLSN I) SN 2017gci, whose peak K-corrected absolute magnitude reaches M-g = -21.5 mag. Its photometric and spectroscopic evolution includes features of both slow- and of fast-evolving SLSN I, thus favoring a continuum distribution between the two SLSN-I subclasses. In particular, similarly to other SLSNe I, the multiband light curves (LCs) of SN 2017gci show two re-brightenings at about 103 and 142 d after the maximum light. Interestingly, this broadly agrees with a broad emission feature emerging around 6520 angstrom after similar to 51 d from the maximum light, which is followed by a sharp knee in the LC. If we interpret this feature as H alpha, this could support the fact that the bumps are the signature of late interactions of the ejecta with a (hydrogen-rich) circumstellar material. Then we fitted magnetar- and CSM-interaction-powered synthetic LCs on to the bolometric one of SN 2017gci. In the magnetar case, the fit suggests a polar magnetic field B-p similar or equal to 6 x 10(14) G, an initial period of the magnetar P-initial similar or equal to 2.8 ms, an ejecta mass M-ejecta similar or equal to 9M(circle dot) and an ejecta opacity kappa similar or equal to 0.08 cm(2) g(-1). A CSM-interaction scenario would imply a CSM mass similar or equal to 5 M-circle dot and an ejecta mass similar or equal to 12M(circle dot). Finally, the nebular spectrum of phase + 187 d was modeled, deriving a mass of similar or equal to 10 M-circle dot for the ejecta. Our models suggest that either a magnetar or CSM interaction might be the power sources for SN 2017gci and that its progenitor was a massive (40 M-circle dot) star.
  •  
37.
  • Gutiérrez, C. P., et al. (författare)
  • SN 2017ivv : two years of evolution of a transitional Type II supernova
  • 2020
  • Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 499:1, s. 974-992
  • Tidskriftsartikel (refereegranskat)abstract
    • We present the photometric and spectroscopic evolution of the Type II supernova (SN II) SN 2017ivv (also known as ASASSN-17qp). Located in an extremely faint galaxy (M-r =-10.3 mag), SN 2017ivv shows an unprecedented evolution during the 2 yr of observations. At early times, the light curve shows a fast rise (similar to 6-8 d) to a peak of M-g(max) = -17.84 mag, followed by a very rapid decline of 7.94 +/- 0.48 mag per 100 d in the V band. The extensive photometric coverage at late phases shows that the radioactive tail has two slopes, one steeper than that expected from the decay of Co-56 (between 100 and 350 d), and another slower (after 450 d), probably produced by an additional energy source. From the bolometric light curve, we estimated that the amount of ejected 5(6)Ni is similar to 0.059 +/- 0.003M(circle dot). The nebular spectra of SN 2017ivv show a remarkable transformation that allows the evolution to be split into three phases: (1) H alpha strong phase (<200 d); (2) H alpha weak phase (between 200 and 350 d); and (3) H alpha broad phase (>500 d). We find that the nebular analysis favours a binary progenitor and an asymmetric explosion. Finally, comparing the nebular spectra of SN 2017ivv to models suggests a progenitor with a zero-age main-sequence mass of 15-17M(circle dot).
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38.
  • Kankare, E., et al. (författare)
  • A population of highly energetic transient events in the centres of active galaxies
  • 2017
  • Ingår i: Nature Astronomy. - : Springer Science and Business Media LLC. - 2397-3366. ; 1:12, s. 865-871
  • Tidskriftsartikel (refereegranskat)abstract
    • Recent all-sky surveys have led to the discovery of new types of transients. These include stars disrupted by the central supermassive black hole, and supernovae that are 10-100 times more energetic than typical ones. However, the nature of even more energetic transients that apparently occur in the innermost regions of their host galaxies is hotly debated1-3. Here we report the discovery of the most energetic of these to date: PS1-10adi, with a total radiated energy of similar to 2.3 x 10(52) erg. The slow evolution of its light curve and persistently narrow spectral lines over similar to 3 yr are inconsistent with known types of recurring black hole variability. The observed properties imply powering by shock interaction between expanding material and large quantities of surrounding dense matter. Plausible sources of this expanding material are a star that has been tidally disrupted by the central black hole, or a supernova. Both could satisfy the energy budget. For the former, we would be forced to invoke a new and hitherto unseen variant of a tidally disrupted star, while a supernova origin relies principally on environmental effects resulting from its nuclear location. Remarkably, we also discover that PS1-10adi is not an isolated case. We therefore surmise that this new population of transients has previously been overlooked due to incorrect association with underlying central black hole activity.
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39.
  • Onori, F., et al. (författare)
  • The nuclear transient AT 2017gge : a tidal disruption event in a dusty and gas-rich environment and the awakening of a dormant SMBH
  • 2022
  • Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 517:1, s. 76-98
  • Tidskriftsartikel (refereegranskat)abstract
    • We present the results from a dense multwavelength [optical/UV, near-infrared (IR), and X-ray] follow-up campaign of the nuclear transient AT 2017gge, covering a total of 1698 d from the transient's discovery. The bolometric light curve, the blackbody temperature and radius, the broad H and He i lambda 5876 emission lines and their evolution with time, are all consistent with a tidal disruption event (TDE) nature. A soft X-ray flare is detected with a delay of similar to 200 d with respect to the optical/UV peak and it is rapidly followed by the emergence of a broad He ii lambda 4686 and by a number of long-lasting high ionization coronal emission lines. This indicate a clear connection between a TDE flare and the appearance of extreme coronal line emission (ECLEs). An IR echo, resulting from dust re-radiation of the optical/UV TDE light is observed after the X-ray flare and the associated near-IR spectra show a transient broad feature in correspondence of the He i lambda 10830 and, for the first time in a TDE, a transient high-ionization coronal NIR line (the [Fe xiii] lambda 10798) is also detected. The data are well explained by a scenario in which a TDE occurs in a gas-and-dust rich environment and its optical/UV, soft X-ray, and IR emission have different origins and locations. The optical emission may be produced by stellar debris stream collisions prior to the accretion disc formation, which is instead responsible for the soft X-ray flare, emitted after the end of the circularization process.
  •  
40.
  • Pessi, Priscila Jael, et al. (författare)
  • Broad-emission-line dominated hydrogen-rich luminous supernovae
  • 2023
  • Ingår i: Monthly notices of the Royal Astronomical Society. - 0035-8711 .- 1365-2966. ; 523:4, s. 5315-5340
  • Tidskriftsartikel (refereegranskat)abstract
    • Hydrogen-rich Type II supernovae (SNe II) are the most frequently observed class of core-collapse SNe (CCSNe). However, most studies that analyse large samples of SNe II lack events with absolute peak magnitudes brighter than −18.5 mag at rest-frame optical wavelengths. Thanks to modern surveys, the detected number of such luminous SNe II (LSNe II) is growing. There exist several mechanisms that could produce luminous SNe II. The most popular propose either the presence of a central engine (a magnetar gradually spinning down or a black hole accreting fallback material) or the interaction of supernova ejecta with circumstellar material (CSM) that turns kinetic energy into radiation energy. In this work, we study the light curves and spectral series of a small sample of six LSNe II that show peculiarities in their H α profile, to attempt to understand the underlying powering mechanism. We favour an interaction scenario with CSM that is not dense enough to be optically thick to electron scattering on large scales – thus, no narrow emission lines are observed. This conclusion is based on the observed light curve (higher luminosity, fast decline, blue colours) and spectral features (lack of persistent narrow lines, broad H α emission, lack of H α absorption, weak, or non-existent metal lines) together with comparison to other luminous events available in the literature. We add to the growing evidence that transients powered by ejecta–CSM interaction do not necessarily display persistent narrow emission lines.
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41.
  • Prentice, S. J., et al. (författare)
  • SN 2018gjx reveals that some SNe Ibn are SNe IIb exploding in dense circumstellar material
  • 2020
  • Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 499:1, s. 1450-1467
  • Tidskriftsartikel (refereegranskat)abstract
    • We present the data and analysis of SN 2018gjx, an unusual low-luminosity transient with three distinct spectroscopic phases. Phase I shows a hot blue spectrum with signatures of ionized circumstellar material (CSM), Phase II has the appearance of broad SN features, consistent with those seen in a Type IIb supernova at maximum light, and Phase III is that of a supernova interacting with helium-rich CSM, similar to a Type Ibn supernova. This event provides an apparently rare opportunity to view the inner workings of an interacting supernova. The observed properties can be explained by the explosion of a star in an aspherical CSM. The initial light is emitted from an extended CSM (similar to 4000 R-circle dot), which ionizes the exterior unshocked material. Some days after, the SN photosphere envelops this region, leading to the appearance of a SN IIb. Over time, the photosphere recedes in velocity space, revealing interaction between the supernova ejecta and the CSM that partially obscures the supernova nebular phase. Modelling of the initial spectrum reveals a surface composition consistent with compact H-deficient Wolf-Rayet and Luminous Blue Variable (LBV) stars. Such configurations may not be unusual, with SNe IIb being known to have signs of interaction so at least some SNe IIb and SNe Ibn may be the same phenomena viewed from different angles, or possibly with differing CSM configurations.
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42.
  • Valenti, S., et al. (författare)
  • SN 2009jf : a slow-evolving stripped-envelope core-collapse supernova
  • 2011
  • Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 416:4, s. 3138-3159
  • Tidskriftsartikel (refereegranskat)abstract
    • We present an extensive set of photometric and spectroscopic data for SN 2009jf, a nearby Type Ib supernova (SN), spanning from similar to 20 d before B-band maximum to 1 yr after maximum. We show that SN 2009jf is a slowly evolving and energetic stripped-envelope SN and is likely from a massive progenitor (25-30 M(circle dot)). The large progenitor's mass allows us to explain the complete hydrogen plus helium stripping without invoking the presence of a binary companion. The SN occurred close to a young cluster, in a crowded environment with ongoing star formation. The spectroscopic similarity with the He-poor Type Ic SN 2007gr suggests a common progenitor for some SNe Ib and Ic. The nebular spectra of SN 2009jf are consistent with an asymmetric explosion, with an off-centre dense core. We also find evidence that Herich Ib SNe have a rise time longer than other stripped-envelope SNe, however confirmation of this result and further observations are needed.
  •  
43.
  • Irani, I., et al. (författare)
  • Less Than 1% of Core-collapse Supernovae in the Local Universe Occur in Elliptical Galaxies
  • 2022
  • Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 927:1
  • Tidskriftsartikel (refereegranskat)abstract
    • We present observations of three core-collapse supernovae (CCSNe) in elliptical hosts, detected by the Zwicky Transient Facility Bright Transient Survey (BTS). SN 2019ape is a SN Ic that exploded in the main body of a typical elliptical galaxy. Its properties are consistent with an explosion of a regular SN Ic progenitor. A secondary g-band light-curve peak could indicate interaction of the ejecta with circumstellar material (CSM). An Ha-emitting source at the explosion site suggests a residual local star formation origin. SN 2018fsh and SN 2020uik are SNe II which exploded in the outskirts of elliptical galaxies. SN 2020uik shows typical spectra for SNe II, while SN 2018fsh shows a boxy nebular Ha profile, a signature of CSM interaction. We combine these 3 SNe with 7 events from the literature and analyze their hosts as a sample. We present multi-wavelength photometry of the hosts, and compare this to archival photometry of all BTS hosts. Using the spectroscopically complete BTS, we conclude that 0.3%(+0.3)(-0.1) of all CCSNe occur in elliptical galaxies. We derive star formation rates and stellar masses for the host galaxies and compare them to the properties of other SN hosts. We show that CCSNe in ellipticals have larger physical separations from their hosts compared to SNe Ia in elliptical galaxies, and discuss implications for star-forming activity in elliptical galaxies.
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44.
  • Kangas, T., et al. (författare)
  • Supernova 2013fc in a circumnuclear ring of a luminous infrared galaxy : the big brother of SN 1998S
  • 2016
  • Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 456:1, s. 323-346
  • Tidskriftsartikel (refereegranskat)abstract
    • We present photometric and spectroscopic observations of SN 2013fc, a bright type II supernova (SN) in a circumnuclear star-forming ring in the luminous infrared galaxy ESO 154-G010, observed as part of the Public ESO Spectroscopic Survey of Transient Objects. SN 2013fc is both photometrically and spectroscopically similar to the well-studied type IIn SN 1998S and to the bright type II-L SN 1979C. It exhibits an initial linear decline, followed by a short plateau phase and a tail phase with a decline too fast for Co-56 decay with full. gamma-ray trapping. Initially, the spectrum was blue and featureless. Later on, a strong broad (similar to 8000 km s(-1)) H alpha emission profile became prominent. We apply a STARLIGHT stellar population model fit to the SN location (observed when the SN had faded) to estimate a high extinction of A(V) = 2.9 +/- 0.2 mag and an age of 10(+ 3) (- 2) Myr for the underlying cluster. We compare the SN to SNe 1998S and 1979C and discuss its possible progenitor star considering the similarities to these events. With a peak brightness of B = - 20.46 +/- 0.21 mag, SN 2013fc is 0.9 mag brighter than SN 1998S and of comparable brightness to SN 1979C. We suggest that SN 2013fc was consistent with a massive red supergiant (RSG) progenitor. Recent mass loss probably due to a strong RSG wind created the circumstellar matter illuminated through its interaction with the SN ejecta. We also observe a near- infrared excess, possibly due to newly condensed dust.
  •  
45.
  • Magee, M. R., et al. (författare)
  • The type Iax supernova, SN 2015H A white dwarf deflagration candidate
  • 2016
  • Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 589
  • Tidskriftsartikel (refereegranskat)abstract
    • We present results based on observations of SN 2015H which belongs to the small group of objects similar to SN 2002cx, otherwise known as type Iax supernovae. The availability of deep pre-explosion imaging allowed us to place tight constraints on the explosion epoch. Our observational campaign began approximately one day post-explosion, and extended over a period of about 150 days post maximum light, making it one of the best observed objects of this class to date. We find a peak magnitude of M-r = 17.27 +/- 0.07, and a (Delta m(15))(r) = 0.69 +/- 0.04. Comparing our observations to synthetic spectra generated from simulations of deflagrations of Chandrasekhar mass carbon-oxygen white dwarfs, we find reasonable agreement with models of weak deflagrations that result in the ejection of similar to 0.2 M-circle dot of material containing similar to 0.07 M-circle dot of Ni-56. The model light curve however, evolves more rapidly than observations, suggesting that a higher ejecta mass is to be favoured. Nevertheless, empirical modelling of the pseudo-bolometric light curve suggests that less than or similar to 0.6 M-circle dot of material was ejected, implying that the white dwarf is not completely disrupted, and that a bound remnant is a likely outcome.
  •  
46.
  • Maguire, K., et al. (författare)
  • Using late-time optical and near-infrared spectra to constrain Type Ia supernova explosion properties
  • 2018
  • Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 477:3, s. 3567-3582
  • Tidskriftsartikel (refereegranskat)abstract
    • The late-time spectra of Type Ia supernovae (SNe Ia) are powerful probes of the underlying physics of their explosions. We investigate the late-time optical and near-infrared spectra of seven SNe Ia obtained at the VLT with XShooter at >200 d after explosion. At these epochs, the inner Fe-rich ejecta can be studied. We use a line-fitting analysis to determine the relative line fluxes, velocity shifts, and line widths of prominent features contributing to the spectra ([Fe II], [Ni II], and [Co III]). By focusing on [Fe II] and [Ni II] emission lines in the similar to 7000-7500 angstrom region of the spectrum, we find that the ratio of stable [Ni II] to mainly radioactively produced [Fe II] for most SNe Ia in the sample is consistent with Chandrasekhar-mass delayed-detonation explosion models, as well as sub-Chandrasekhar mass explosions that have metallicity values above solar. The mean measured Ni/Fe abundance of our sample is consistent with the solar value. The more highly ionized [Co III] emission lines are found to be more centrally located in the ejecta and have broader lines than the [Fe II] and [Ni II] features. Our analysis also strengthens previous results that SNe Ia with higher Si II velocities at maximum light preferentially display blueshifted [Fe II] 7155 angstrom lines at late times. Our combined results lead us to speculate that the majority of normal SN Ia explosions produce ejecta distributions that deviate significantly from spherical symmetry.
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47.
  •  
48.
  • Nicholl, M., et al. (författare)
  • On the diversity of superluminous supernovae : ejected mass as the dominant factor
  • 2015
  • Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 452:4, s. 3869-3893
  • Tidskriftsartikel (refereegranskat)abstract
    • We assemble a sample of 24 hydrogen-poor superluminous supernovae (SLSNe). Parameterizing the light-curve shape through rise and decline time-scales shows that the two are highly correlated. Magnetar-powered models can reproduce the correlation, with the diversity in rise and decline rates driven by the diffusion time-scale. Circumstellar interaction models can exhibit a similar rise-decline relation, but only for a narrow range of densities, which may be problematic for these models. We find that SLSNe are approximately 3.5 mag brighter and have light curves three times broader than SNe Ibc, but that the intrinsic shapes are similar. There are a number of SLSNe with particularly broad light curves, possibly indicating two progenitor channels, but statistical tests do not cleanly separate two populations. The general spectral evolution is also presented. Velocities measured from Fe II are similar for SLSNe and SNe Ibc, suggesting that diffusion time differences are dominated by mass or opacity. Flat velocity evolution in most SLSNe suggests a dense shell of ejecta. If opacities in SLSNe are similar to other SNe Ibc, the average ejected mass is higher by a factor 2-3. Assuming. = 0.1 cm(2) g(-1), we estimate a mean (median) SLSN ejecta mass of 10 M-circle dot (6 M-circle dot), with a range of 3-30 M-circle dot. Doubling the assumed opacity brings the masses closer to normal SNe Ibc, but with a high-mass tail. The most probable mechanism for generating SLSNe seems to be the core collapse of a very massive hydrogen-poor star, forming a millisecond magnetar.
  •  
49.
  • Pastorello, A., et al. (författare)
  • INTERACTING SUPERNOVAE AND SUPERNOVA IMPOSTORS : SN 2009ip, IS THIS THE END?
  • 2013
  • Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 767:1, s. 1-
  • Tidskriftsartikel (refereegranskat)abstract
    • We report the results of a three-year-long dedicated monitoring campaign of a restless luminous blue variable (LBV) in NGC 7259. The object, named SN 2009ip, was observed photometrically and spectroscopically in the optical and near-infrared domains. We monitored a number of erupting episodes in the past few years, and increased the density of our observations during eruptive episodes. In this paper, we present the full historical data set from 2009 to 2012 with multi-wavelength dense coverage of the two high-luminosity events between 2012 August and September. We construct bolometric light curves and measure the total luminosities of these eruptive or explosive events. We label them the 2012a event (lasting similar to 50 days) with a peak of 3x10(41) erg s(-1), and the 2012b event (14 day rise time, still ongoing) with a peak of 8 x 1042 erg s(-1). The latter event reached an absolute R-band magnitude of about -18, comparable to that of a core-collapse supernova (SN). Our historical monitoring has detected high-velocity spectral features (similar to 13,000 km s(-1)) in 2011 September, one year before the current SN-like event. This implies that the detection of such high-velocity outflows cannot, conclusively, point to a core-collapse SN origin. We suggest that the initial peak in the 2012a event was unlikely to be due to a faint core-collapse SN. We propose that the high intrinsic luminosity of the latest peak, the variability history of SN 2009ip, and the detection of broad spectral lines indicative of high-velocity ejecta are consistent with a pulsational pair-instability event, and that the star may have survived the last outburst. The question of the survival of the LBV progenitor star and its future fate remain open issues, only to be answered with future monitoring of this historically unique explosion.
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50.
  • Pursiainen, M., et al. (författare)
  • Polarimetry of hydrogen-poor superluminous supernovae
  • 2023
  • Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 674
  • Tidskriftsartikel (refereegranskat)abstract
    • We present linear polarimetry for seven hydrogen-poor superluminous supernovae (SLSNe-I) of which only one has previously published polarimetric data. The best-studied event is SN 2017gci, for which we present two epochs of spectropolarimetry at +3 d and +29 d post-peak in rest frame, accompanied by four epochs of imaging polarimetry up to +108 d. The spectropolarimetry at +3 d shows increasing polarisation degree P towards the redder wavelengths and exhibits signs of axial symmetry, but at +29 d, P similar to 0 throughout the spectrum, implying that the photosphere of SN 2017gci evolved from a slightly aspherical configuration to a more spherical one in the first month post-peak. However, an increase of P to similar to 0.5% at similar to+55 d accompanied by a different orientation of the axial symmetry compared to +3 d implies the presence of additional sources of polarisation at this phase. The increase in polarisation is possibly caused by interaction with circumstellar matter (CSM), as already suggested by a knee in the light curve and a possible detection of broad H alpha emission at the same phase. We also analysed the sample of all 16 SLSNe-I with polarimetric measurements to date. The data taken during the early spectroscopic phase show consistently low polarisation, indicating at least nearly spherical photospheres. No clear relation between the polarimetry and spectral phase was seen when the spectra resemble Type Ic SNe during the photospheric and nebular phases. The light-curve decline rate, which spans a factor of eight, also shows no clear relation with the polarisation properties. While only slow-evolving SLSNe-I have shown non-zero polarisation, the fast-evolving ones have not been observed at sufficiently late times to conclude that none of them exhibit changing P. However, the four SLSNe-I with increasing polarisation degree also have irregular light-curve declines. For up to half of them, the photometric, spectroscopic, and polarimetric properties are affected by CSM interaction. As such, CSM interaction clearly plays an important role in understanding the polarimetric evolution of SLSNe-I.
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