| 1. |
- Andreoni, Igor, et al.
(författare)
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GROWTH on S190814bv : Deep Synoptic Limits on the Optical/Near-infrared Counterpart to a Neutron Star-Black Hole Merger
- 2020
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 890:2
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Tidskriftsartikel (refereegranskat)abstract
- On 2019 August 14, the Advanced LIGO and Virgo interferometers detected the high-significance gravitational wave (GW) signal S190814bv. The GW data indicated that the event resulted from a neutron star-black hole (NSBH) merger, or potentially a low-mass binary BH merger. Due to the low false-alarm rate and the precise localization (23 deg(2) at 90%), S190814bv presented the community with the best opportunity yet to directly observe an optical/near-infrared counterpart to an NSBH merger. To search for potential counterparts, the GROWTH Collaboration performed real-time image subtraction on six nights of public Dark Energy Camera images acquired in the 3 weeks following the merger, covering >98% of the localization probability. Using a worldwide network of follow-up facilities, we systematically undertook spectroscopy and imaging of optical counterpart candidates. Combining these data with a photometric redshift catalog, we ruled out each candidate as the counterpart to S190814bv and placed deep, uniform limits on the optical emission associated with S190814bv. For the nearest consistent GW distance, radiative transfer simulations of NSBH mergers constrain the ejecta mass of S190814bv to be M-ej < 0.04 M-circle dot at polar viewing angles, or M-ej < 0.03 M-circle dot if the opacity is kappa < 2 cm(2)g(-1). Assuming a tidal deformability for the NS at the high end of the range compatible with GW170817 results, our limits would constrain the BH spin component aligned with the orbital momentum to be chi < 0.7 for mass ratios Q < 6, with weaker constraints for more compact NSs.
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| 2. |
- Arcavi, Iair, et al.
(författare)
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Energetic eruptions leading to a peculiar hydrogen-rich explosion of a massive star
- 2017
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 551:7679, s. 210-213
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Tidskriftsartikel (refereegranskat)abstract
- Every supernova so far observed has been considered to be the terminal explosion of a star. Moreover, all supernovae with absorption lines in their spectra show those lines decreasing in velocity over time, as the ejecta expand and thin, revealing slower-moving material that was previously hidden. In addition, every supernova that exhibits the absorption lines of hydrogen has one main light-curve peak, or a plateau in luminosity, lasting approximately 100 days before declining(1). Here we report observations of iPTF14hls, an event that has spectra identical to a hydrogen-rich core-collapse supernova, but characteristics that differ extensively from those of known supernovae. The light curve has at least five peaks and remains bright for more than 600 days; the absorption lines show little to no decrease in velocity; and the radius of the line-forming region is more than an order of magnitude bigger than the radius of the photosphere derived from the continuum emission. These characteristics are consistent with a shell of several tens of solar masses ejected by the progenitor star at supernova-level energies a few hundred days before a terminal explosion. Another possible eruption was recorded at the same position in 1954. Multiple energetic pre-supernova eruptions are expected to occur in stars of 95 to 130 solar masses, which experience the pulsational pair instability(2-5). That model, however, does not account for the continued presence of hydrogen, or the energetics observed here. Another mechanism for the violent ejection of mass in massive stars may be required.
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| 3. |
- Kamble, Atish, et al.
(författare)
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RADIO OBSERVATIONS REVEAL A SMOOTH CIRCUMSTELLAR ENVIRONMENT AROUND THE EXTRAORDINARY TYPE Ib SUPERNOVA 2012au
- 2014
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 797:1, s. 2-
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Tidskriftsartikel (refereegranskat)abstract
- We present extensive radio and X-ray observations of SN 2012au, an energetic, radio-luminous supernova of Type Ib that exhibits multi-wavelength properties bridging subsets of hydrogen-poor superluminous supernovae, hypernovae, and normal core-collapse supernovae. The observations closely follow models of synchrotron emission from a shock-heated circumburst medium that has a wind density profile (rho alpha r(-2)). We infer a sub-relativistic velocity for the shock wave v approximate to 0.2 c and a radius of r approximate to 1.4 x 10(16) cm at 25 days after the estimated date of explosion. For a wind velocity of 1000 km s(-1), we determine the mass-loss rate of the progenitor to be M = 3.6 x 10(-6) M-circle dot yr(-1), consistent with the estimates from X-ray observations. We estimate the total internal energy of the radio-emitting material to be E approximate to 10(47) crg, which is intermediate to SN 1998bw and SN 2002ap. The evolution of the radio light curve of SN 2012au is in agreement with its interaction with a smoothly distributed circumburst medium and the absence of stellar shells ejected from previous outbursts out to r approximate to 10(17) cm from the supernova site. We conclude that the bright radio emission from SN 2012au was not dissimilar from other core-collapse supernovae despite its extraordinary optical properties, and that the evolution of the SN 2012au progenitor star was relatively quiet, marked with a steady mass loss, during the final years preceding explosion.
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| 4. |
- Li, Wenxiong, et al.
(författare)
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Rapidly Evolving Transients in Archival ZTF Public Alerts
- 2023
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Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 955:2
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Tidskriftsartikel (refereegranskat)abstract
- We search the archival Zwicky Transient Facility public survey for rapidly evolving transient (RET) candidates based on well-defined criteria between 2018 May and 2021 December. The search yielded 19 bona fide RET candidates, corresponding to a discovery rate of ∼5.2 events per year. Even with a Galactic latitude cut of 20°, eight of the 19 events (∼42%) are Galactic, including one with a light-curve shape closely resembling that of the GW170817 kilonova (KN). An additional event is a nova in M31. Four out of the 19 events (∼21%) are confirmed extragalactic RETs (one confirmed here for the first time) and the origin of six additional events cannot be determined. We did not find any extragalactic events resembling the GW170817 KN, from which we obtain an upper limit on the volumetric rate of GW170817-like KNe of R ≤ 2400 Gpc−3 yr−1 (95% confidence). These results can be used for quantifying contaminants to RET searches in transient alert streams, specifically when searching for KNe independently of gravitational-wave and gamma-ray-burst triggers.
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| 5. |
- Piran, Tsvi, et al.
(författare)
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The electromagnetic signals of compact binary mergers
- 2013
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 430:3, s. 2121-2136
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Tidskriftsartikel (refereegranskat)abstract
- Compact binary mergers are prime sources of gravitational waves (GWs), targeted by current and next generation detectors. The question 'what is the observable electromagnetic (EM) signature of a compact binary merger?' is an intriguing one with crucial consequences to the quest for GWs. We present a large set of numerical simulations that focus on the EM signals that emerge from the dynamically ejected subrelativistic material. These outflows produce on a time-scale of a day macronovae - short-lived infrared (IR) to ultraviolet (UV) signals powered by radioactive decay. Like in regular supernovae the interaction of this outflow with the surrounding matter inevitably leads to a long-lasting remnant. We calculate the expected radio signals of these remnants on time-scales longer than a year, when the subrelativistic ejecta dominate the emission. We discuss their detectability in 1.4 GHz and 150 MHz and compare it with an updated estimate of the detectability of short gamma-ray bursts' orphan afterglows (which are produced by a different component of this outflow). We find that mergers with characteristics similar to those of the Galactic neutron star binary population (similar masses and typical circummerger Galactic disc density of similar to 1 cm(-3)) that take place at the detection horizon of advanced GW detectors (300 Mpc) yield 1.4 GHz [150 MHz] signals of similar to 50 [300] mu Jy, for several years. The signal on time-scales of weeks is dominated by the mildly and/or ultrarelativistic outflow, which is not accounted for by our simulations, and is expected to be even brighter. Upcoming all sky surveys are expected to detect a few dozen, and possibly more, merger remnants at any given time thereby providing robust lower limits to the mergers rate even before the advanced GW detectors become operational. The macronovae signals from the same distance peak in the IR to UV range at an observed magnitude that may be as bright as 22-23 about 10 h after the merger but dimmer, redder and longer if the opacity is larger.
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