| 1. |
- 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.
|
|
| 2. |
- 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.
|
|
| 3. |
- 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).
|
|
| 4. |
- 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.
|
|
| 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.
|
|
| 6. |
- Davis, S., et al.
(författare)
-
SN 2013ai : A Link between Hydrogen-rich and Hydrogen-poor Core-collapse Supernovae
- 2021
-
Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 909:2
-
Tidskriftsartikel (refereegranskat)abstract
- We present a study of the optical and near-infrared (NIR) spectra of SN 2013ai along with its light curves. These data range from discovery until 380 days after explosion. SN 2013ai is a fast declining Type II supernova (SN II) with an unusually long rise time, 18.9 2.7 days in the V-band, and a bright V-band peak absolute magnitude of -18.7 0.06 mag. The spectra are dominated by hydrogen features in the optical and NIR. The spectral features of SN 2013ai are unique in their expansion velocities, which, when compared to large samples of SNe II, are more than 1,000 km s(-1) faster at 50 days past explosion. In addition, the long rise time of the light curve more closely resembles SNe IIb rather than SNe II. If SN 2013ai is coeval with a nearby compact cluster, we infer a progenitor zero-age main-sequence mass of similar to 17 M. After performing light-curve modeling, we find that SN 2013ai could be the result of the explosion of a star with little hydrogen mass, a large amount of synthesized Ni-56, 0.3-0.4 M, and an explosion energy of 2.5-3.0 x 10(51) erg. The density structure and expansion velocities of SN 2013ai are similar to those of the prototypical SN IIb, SN 1993J. However, SN 2013ai shows no strong helium features in the optical, likely due to the presence of a dense core that prevents the majority of gamma-rays from escaping to excite helium. Our analysis suggests that SN 2013ai could be a link between SNe II and stripped-envelope SNe.
|
|
| 7. |
- Moran, S., et al.
(författare)
-
A long life of excess : The interacting transient SN 2017hcc
- 2023
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 669
-
Tidskriftsartikel (refereegranskat)abstract
- In this study we present the results of a five-year follow-up campaign of the long-lived type IIn supernova SN 2017hcc, found in a spiral dwarf host of near-solar metallicity. The long rise time (57 ± 2 days, ATLAS o band) and high luminosity (peaking at −20.78 ± 0.01 mag in the ATLAS o band) point towards an interaction of massive ejecta with massive and dense circumstellar material (CSM). The evolution of SN 2017hcc is slow, both spectroscopically and photometrically, reminiscent of the long-lived type IIn, SN 2010jl. An infrared (IR) excess was apparent soon after the peak, and blueshifts were noticeable in the Balmer lines starting from a few hundred days, but appeared to be fading by around +1200 d. We posit that an IR light echo from pre-existing dust dominates at early times, with some possible condensation of new dust grains occurring at epochs ≳+800 d.
|
|
| 8. |
- 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.
|
|
| 9. |
- Stritzinger, M. D., et al.
(författare)
-
The carbon-rich type Ic supernova 2016adj in the iconic dust lane of Centaurus A : Potential signatures of an interaction with circumstellar hydrogen
- 2024
-
Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 686
-
Tidskriftsartikel (refereegranskat)abstract
- We present a comprehensive data set of supernova (SN) 2016adj located within the central dust lane of Centaurus A. SN 2016adj is significantly reddened and after correcting the peak apparent B-band magnitude (mB = 17.48 ± 0.05) for Milky Way reddening and our inferred host-galaxy reddening parameters (i.e., RVhost = 5.7±0.7 and AVhost = 6.3 ± 0.2 mag), we estimated it reached a peak absolute magnitude of MB ∼ −18. A detailed inspection of the optical and near-infrared (NIR) spectroscopic time series reveals a carbon-rich SN Ic and not a SN Ib/IIb as previously suggested in the literature. The NIR spectra show prevalent carbon-monoxide formation occurring already by +41 days past B-band maximum, which is ≈11 days earlier than previously reported in the literature for this object. Interestingly, around two months past maximum, the NIR spectrum of SN 2016adj begins to exhibit H features, with a +97 days medium resolution spectrum revealing both Paschen and Bracket lines with absorption minima of ∼2000 km s−1, full-width-half-maximum emission velocities of ∼1000 km s−1, and emission line ratios consistent with a dense emission region. We speculate that these attributes are due to a circumstellar interaction (CSI) between the rapidly expanding SN ejecta and a H-rich shell of material that formed during the pre-SN phase. A bolometric light curve was constructed and a semi-analytical model fit suggests the SN synthesized 0.5 M⊙ of 56Ni and ejected 4.7 M⊙ of material, though these values should be approached with caution given the large uncertainties associated with the adopted reddening parameters and known light echo emission. Finally, inspection of the Hubble Space Telescope archival data yielded no progenitor detection.
|
|
| 10. |
- 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).
|
|
