| 1. |
- Jencson, Jacob E., et al.
(författare)
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AT 2019qyl in NGC 300 : Internal Collisions in the Early Outflow from a Very Fast Nova in a Symbiotic Binary
- 2021
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 920:2
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Tidskriftsartikel (refereegranskat)abstract
- Nova eruptions, thermonuclear explosions on the surfaces of white dwarfs (WDs), are now recognized to be among the most common shock-powered astrophysical transients. We present the early discovery and rapid ultraviolet (UV), optical, and infrared (IR) temporal development of AT 2019qyl, a recent nova in the nearby Sculptor Group galaxy NGC 300. The light curve shows a rapid rise lasting ≲1 day, reaching a peak absolute magnitude of MV = −9.2 mag and a very fast decline, fading by 2 mag over 3.5 days. A steep dropoff in the light curves after 71 days and the rapid decline timescale suggest a low-mass ejection from a massive WD with MWD ≳ 1.2 M⊙. We present an unprecedented view of the early spectroscopic evolution of such an event. Three spectra prior to the peak reveal a complex, multicomponent outflow giving rise to internal collisions and shocks in the ejecta of an He/N-class nova. We identify a coincident IR-variable counterpart in the extensive preeruption coverage of the transient location and infer the presence of a symbiotic progenitor system with an O-rich asymptotic-giant-branch donor star, as well as evidence for an earlier UV-bright outburst in 2014. We suggest that AT 2019qyl is analogous to the subset of Galactic recurrent novae with red-giant companions such as RS Oph and other embedded nova systems like V407 Cyg. Our observations provide new evidence that internal shocks between multiple, distinct outflow components likely contribute to the generation of the shock-powered emission from such systems.
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| 2. |
- Wang, Qinan, et al.
(författare)
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Revealing the Progenitor of SN 2021zby through Analysis of the TESS Shock-cooling Light Curve
- 2023
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8205 .- 2041-8213. ; 943:2
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Tidskriftsartikel (refereegranskat)abstract
- We present early observations and analysis of the double-peaked Type IIb supernova (SN IIb) SN 2021zby. TESS captured the prominent early shock-cooling peak of SN 2021zby within the first ∼10 days after explosion with a 30 minute cadence. We present optical and near-infrared spectral series of SN 2021zby, including three spectra during the shock-cooling phase. Using a multiband model fit, we find that the inferred properties of its progenitor are consistent with a red supergiant or yellow supergiant, with an envelope mass of ∼0.30–0.65 M⊙ and an envelope radius of ∼120–300 R⊙. These inferred progenitor properties are similar to those of other SNe IIb with a double-peaked feature, such as SNe 1993J, 2011dh, 2016gkg, and 2017jgh. This study further validates the importance of the high cadence and early coverage in resolving the shape of the shock-cooling light curve, while the multiband observations, particularly UV, are also necessary to fully constrain the progenitor properties.
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| 3. |
- Aamer, Aysha, et al.
(författare)
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A precursor plateau and pre-maximum [O ii] emission in the superluminous SN2019szu : a pulsational pair-instability candidate
- 2023
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Ingår i: Monthly notices of the Royal Astronomical Society. - 0035-8711 .- 1365-2966. ; 527:4, s. 11970-11995
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Tidskriftsartikel (refereegranskat)abstract
- We present a detailed study on SN2019szu, a Type I superluminous supernova at z = 0.213 that displayed unique photometric and spectroscopic properties. Pan-STARRS and ZTF forced photometry show a pre-explosion plateau lasting ∼40 d. Unlike other SLSNe that show decreasing photospheric temperatures with time, the optical colours show an apparent temperature increase from ∼15 000 to ∼20 000 K over the first 70 d, likely caused by an additional pseudo-continuum in the spectrum. Remarkably, the spectrum displays a forbidden emission line (likely attributed to λλ7320,7330) visible 16 d before maximum light, inconsistent with an apparently compact photosphere. This identification is further strengthened by the appearances of [O III] λλ4959, 5007, and [O III] λ4363 seen in the spectrum. Comparing with nebular spectral models, we find that the oxygen line fluxes and ratios can be reproduced with ∼0.25 M⊙ of oxygen-rich material with a density of ∼10−15 g cm−3. The low density suggests a circumstellar origin, but the early onset of the emission lines requires that this material was ejected within the final months before the terminal explosion, consistent with the timing of the precursor plateau. Interaction with denser material closer to the explosion likely produced the pseudo-continuum bluewards of ∼5500 Å. We suggest that this event is one of the best candidates to date for a pulsational pair-instability ejection, with early pulses providing the low density material needed for the formation of the forbidden emission line, and collisions between the final shells of ejected material producing the pre-explosion plateau.
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| 4. |
- Andreoni, Igor, et al.
(författare)
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Target-of-opportunity Observations of Gravitational-wave Events with Vera C. Rubin Observatory
- 2022
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Ingår i: Astrophysical Journal Supplement Series. - : American Astronomical Society. - 0067-0049 .- 1538-4365. ; 260:1
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Tidskriftsartikel (refereegranskat)abstract
- The discovery of the electromagnetic counterpart to the binary neutron star (NS) merger GW170817 has opened the era of gravitational-wave multimessenger astronomy. Rapid identification of the optical/infrared kilonova enabled a precise localization of the source, which paved the way to deep multiwavelength follow-up and its myriad of related science results. Fully exploiting this new territory of exploration requires the acquisition of electromagnetic data from samples of NS mergers and other gravitational-wave sources. After GW170817, the frontier is now to map the diversity of kilonova properties and provide more stringent constraints on the Hubble constant, and enable new tests of fundamental physics. The Vera C. Rubin Observatory's Legacy Survey of Space and Time can play a key role in this field in the 2020s, when an improved network of gravitational-wave detectors is expected to reach a sensitivity that will enable the discovery of a high rate of merger events involving NSs (∼tens per year) out to distances of several hundred megaparsecs. We design comprehensive target-of-opportunity observing strategies for follow-up of gravitational-wave triggers that will make the Rubin Observatory the premier instrument for discovery and early characterization of NS and other compact-object mergers, and yet unknown classes of gravitational-wave events.
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| 5. |
- Arendt, Richard G., et al.
(författare)
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JWST NIRCam Observations of SN 1987A : Spitzer Comparison and Spectral Decomposition
- 2023
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 959:2
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Tidskriftsartikel (refereegranskat)abstract
- JWST Near Infrared Camera (NIRCam) observations at 1.5–4.5 μm have provided broadband and narrowband imaging of the evolving remnant of SN 1987A with unparalleled sensitivity and spatial resolution. Comparing with previous marginally spatially resolved Spitzer Infrared Array Camera (IRAC) observations from 2004 to 2019 confirms that the emission arises from the circumstellar equatorial ring (ER), and the current brightness at 3.6 and 4.5 μm was accurately predicted by extrapolation of the declining brightness tracked by IRAC. Despite the regular light curve, the NIRCam observations clearly reveal that much of this emission is from a newly developing outer portion of the ER. Spots in the outer ER tend to lie at position angles in between the well-known ER hotspots. We show that the bulk of the emission in the field can be represented by five standard spectral energy distributions, each with a distinct origin and spatial distribution. This spectral decomposition provides a powerful technique for distinguishing overlapping emission from the circumstellar medium and the supernova ejecta, excited by the forward and reverse shocks, respectively.
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| 6. |
- Barna, Barnabas, et al.
(författare)
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SN 2019muj-a well-observed Type Iax supernova that bridges the luminosity gap of the class
- 2021
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 501:1, s. 1078-1099
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Tidskriftsartikel (refereegranskat)abstract
- We present early-time (t < +50 d) observations of SN 2019muj (=ASASSN-19tr), one of the best-observed members of the peculiar SN Iax class. Ultraviolet and optical photometric and optical and near-infrared spectroscopic follow-up started from similar to 5 d before maximum light [t(max)(B) on 58707.8 MJD] and covers the photospheric phase. The early observations allow us to estimate the physical properties of the ejecta and characterize the possible divergence from a uniform chemical abundance structure. The estimated bolometric light-curve peaks at 1.05 x 10(42) erg s(-1) and indicates that only 0.031 M-circle dot of Ni-56 was produced, making SN 2019muj a moderate luminosity object in the Iax class with peak absolute magnitude of M-V = -16.4 mag. The estimated date of explosion is t(0) = 58698.2 MJD and implies a short rise time of t(rise) = 9.6 d in B band. We fit of the spectroscopic data by synthetic spectra, calculated via the radiative transfer code TARDIS. Adopting the partially stratified abundance template based on brighter SNe Iax provides a good match with SN 2019muj. However, without earlier spectra, the need for stratification cannot be stated in most of the elements, except carbon, which is allowed to appear in the outer layers only. SN 2019muj provides a unique opportunity to link extremely low-luminosity SNe Iax to well-studied, brighter SNe Iax.
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| 7. |
- Brout, Dillon, et al.
(författare)
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The Pantheon+ analysis : cosmological constraints
- 2022
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Ingår i: Astrophysical Journal. - : Institute of Physics (IOP). - 0004-637X .- 1538-4357. ; 938:2
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Tidskriftsartikel (refereegranskat)abstract
- We present constraints on cosmological parameters from the Pantheon+ analysis of 1701 light curves of 1550 distinct Type Ia supernovae (SNe Ia) ranging in redshift from z = 0.001 to 2.26. This work features an increased sample size from the addition of multiple cross-calibrated photometric systems of SNe covering an increased redshift span, and improved treatments of systematic uncertainties in comparison to the original Pantheon analysis, which together result in a factor of 2 improvement in cosmological constraining power. For a flat ΛCDM model, we find ΩM = 0.334 ± 0.018 from SNe Ia alone. For a flat w0CDM model, we measure w0 = −0.90 ± 0.14 from SNe Ia alone, H0 = 73.5 ± 1.1 km s−1 Mpc−1 when including the Cepheid host distances and covariance (SH0ES), and w0 = -0.978-+0.0310.024 when combining the SN likelihood with Planck constraints from the cosmic microwave background (CMB) and baryon acoustic oscillations (BAO); both w0 values are consistent with a cosmological constant. We also present the most precise measurements to date on the evolution of dark energy in a flat w0waCDM universe, and measure wa = -0.1-+2.00.9 from Pantheon+ SNe Ia alone, H0 = 73.3 ± 1.1 km s−1 Mpc−1 when including SH0ES Cepheid distances, and wa = -0.65-+0.320.28 when combining Pantheon+ SNe Ia with CMB and BAO data. Finally, we find that systematic uncertainties in the use of SNe Ia along the distance ladder comprise less than one-third of the total uncertainty in the measurement of H0 and cannot explain the present “Hubble tension” between local measurements and early universe predictions from the cosmological model.
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| 8. |
- Calamida, Annalisa, et al.
(författare)
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The Not so Simple Stellar System ω Cen. II. Evidence in Support of a Merging Scenario
- 2020
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 891:2
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Tidskriftsartikel (refereegranskat)abstract
- We present multiband photometry covering ∼5° × 5° across ω Cen collected with the Dark Energy Camera on the 4 m Blanco telescope, combined with Hubble Space Telescope and Wide Field Imager data for the central regions. The unprecedented photometric accuracy and field coverage allows us to confirm the different spatial distribution of blue and red main-sequence stars, and of red giant branch (RGB) stars with different metallicities. The ratio of the number of blue to red main-sequence stars shows that the blue main-sequence stellar subpopulation has a more extended spatial distribution compared to the red main-sequence one, with the frequency of blue main-sequence stars increasing at a distance of ∼20′ from ω Cen's center. Similarly, the more metal-rich RGB stars show a more extended spatial distribution compared to the more metal-poor ones in the outskirts of the cluster. Moreover, the centers of the distributions of metal-rich and metal-poor RGB stars are shifted in different directions with respect to the geometrical center of ω Cen. We constructed stellar density profiles for the blue and red main-sequence stars; they show that the blue main-sequence stellar subpopulation has a more extended spatial distribution compared to the red main-sequence one in the outskirts of ω Cen, confirming the results based on the number ratio. We also computed the ellipticity profile of ω Cen, which has a maximum value of 0.16 at a distance of ∼8′ from the center, and a minimum of 0.05 at ∼30′; the average ellipticity is ∼0.10. The circumstantial evidence presented in this work suggests a merging scenario for the formation of the peculiar stellar system ω Cen.
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| 9. |
- Cikota, Aleksandar, et al.
(författare)
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Testing the magnetar scenario for superluminous supernovae with circular polarimetry
- 2018
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 479:4, s. 4984-4990
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Tidskriftsartikel (refereegranskat)abstract
- Superluminous supernovae (SLSNe) are at least similar to 5 times more luminous than common supernovae. Especially hydrogen-poor SLSN-I are difficult to explain with conventional powering mechanisms. One possible scenario that might explain such luminosities is that SLSNe-I are powered by an internal engine, such as a magnetar or an accreting black hole. Strong magnetic fields or collimated jets can circularly polarize light. In this work, we measured circular polarization of two SLSNe-I with the FOcal Reducer and low dispersion Spectrograph (FORS2) mounted at the ESO's Very Large Telescope. PS17bek, a fast-evolving SLSN-I, was observed around peak, while OGLE16dmu, a slowly evolving SLSN-I, was observed 100 d after maximum. Neither SLSN shows evidence of circularly polarized light; however, these non-detections do not rule out the magnetar scenario as the powering engine for SLSNe-I. We calculate the strength of the magnetic field and the expected circular polarization as a function of distance from the magnetar, which decreases very fast. Additionally, we observed no significant linear polarization for PS17bek at four epochs, suggesting that the photosphere near peak is close to spherical symmetry.
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| 10. |
- Foley, Ryan J., et al.
(författare)
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ON THE PROGENITOR AND SUPERNOVA OF THE SN 2002cx-LIKE SUPERNOVA 2008ge
- 2010
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Ingår i: Astronomical Journal. - : American Astronomical Society. - 0004-6256 .- 1538-3881. ; 140:5, s. 1321-1328
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Tidskriftsartikel (refereegranskat)abstract
- We present observations of supernova (SN) 2008ge, which is spectroscopically similar to the peculiar SN 2002cx, and its pre-explosion site indicating that its progenitor was probably a white dwarf. NGC 1527, the host galaxy of SN 2008ge, is an S0 galaxy with no evidence of star formation or massive stars. Astrometrically matching late-time imaging of SN 2008ge to pre-explosion Hubble Space Telescope imaging, we constrain the luminosity of the progenitor star. Since SN 2008ge has no indication of hydrogen or helium in its spectrum, its progenitor must have lost its outer layers before exploding, meaning that it is a white dwarf, a Wolf-Rayet star, or a lower-mass star in a binary system. Observations of the host galaxy show no signs of individual massive stars, star clusters, or H (II) regions at the SN position or anywhere else, making a Wolf-Rayet progenitor unlikely. Late-time spectroscopy of SN 2008ge shows strong [Fe (II)] lines with large velocity widths compared to other members of this class at similar epochs. These previously unseen features indicate that a significant amount of the SN ejecta is Fe (presumably the result of the radioactive decay of Ni-56 generated in the SN), further supporting a thermonuclear explosion. Placing the observations of SN 2008ge in the context of observations of other objects in the same class of SNe, we suggest that the progenitor was most likely a white dwarf.
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