1. 
 Cunningham, Virginia, et al.
(författare)

GRB 160625B : Evidence for a Gaussianshaped Jet
 2020

Ingår i: Astrophysical Journal.  : American Astronomical Society.  0004637X . 15384357. ; 904:2

Tidskriftsartikel (refereegranskat)abstract
 We present multiwavelength modeling of the afterglow from the long gammaray burst (GRB) 160625B using Markov Chain Monte Carlo techniques of the afterglowpy Python package. GRB 160625B is an extremely bright burst with a rich set of observations spanning from radio to gammaray frequencies. These observations range from similar to 0.1 days to >1000 days, thus making this event extremely well suited to such modeling. In this work we compare tophat and Gaussian jet structure types in order to find bestfit values for the GRB jet collimation angle, viewing angle, and other physical parameters. We find that a Gaussianshaped jet is preferred (2.7 sigma5.3 sigma) over the traditional tophat model. Our estimate for the opening angle of the burst ranges from 126 to 390, depending on jetshape model. We also discuss the implications that assumptions on jet shape, viewing angle, and particularly the participation a fraction of electrons have on the final estimation of GRB intrinsic energy release and the resulting energy budget of the relativistic outflow. Most notably, allowing the participation fraction to vary results in an estimated total relativistic energy of similar to 10(53) erg. This is two orders of magnitude higher than when the total fraction is assumed to be unity; thus, this parameter has strong relevance for placing constraints on long GRB central engines, details of the circumburst media, and host environment.


2. 
 Kasliwal, Mansi M., et al.
(författare)

Kilonova Luminosity Function Constraints Based on Zwicky Transient Facility Searches for 13 Neutron Star Merger Triggers during O3
 2020

Ingår i: Astrophysical Journal.  : American Astronomical Society.  0004637X . 15384357. ; 905:2

Tidskriftsartikel (refereegranskat)abstract
 We present a systematic search for optical counterparts to 13 gravitational wave (GW) triggers involving at least one neutron star during LIGO/Virgo's third observing run (O3). We searched binary neutron star (BNS) and neutron star black hole (NSBH) merger localizations with the Zwicky Transient Facility (ZTF) and undertook followup with the Global Relay of Observatories Watching Transients Happen (GROWTH) collaboration. The GW triggers had a median localization area of 4480 deg(2), a median distance of 267 Mpc, and falsealarm rates ranging from 1.5 to 10(25) yr(1). The ZTF coverage in the g and r bands had a median enclosed probability of 39%, median depth of 20.8 mag, and median time lag between merger and the start of observations of 1.5 hr. The O3 followup by the GROWTH team comprised 340 UltraViolet/Optical/InfraRed (UVOIR) photometric points, 64 OIR spectra, and three radio images using 17 different telescopes. We find no promising kilonovae (radioactivitypowered counterparts), and we show how to convert the upper limits to constrain the underlying kilonova luminosity function. Initially, we assume that all GW triggers are bona fide astrophysical events regardless of falsealarm rate and that kilonovae accompanying BNS and NSBH mergers are drawn from a common population; later, we relax these assumptions. Assuming that all kilonovae are at least as luminous as the discovery magnitude of GW170817 (16.1 mag), we calculate that our joint probability of detecting zero kilonovae is only 4.2%. If we assume that all kilonovae are brighter than 16.6 mag (the extrapolated peak magnitude of GW170817) and fade at a rate of 1 mag day(1) (similar to GW170817), the joint probability of zero detections is 7%. If we separate the NSBH and BNS populations based on the online classifications, the joint probability of zero detections, assuming all kilonovae are brighter than 16.6 mag, is 9.7% for NSBH and 7.9% for BNS mergers. Moreover, no more than <57% (<89%) of putative kilonovae could be brighter than 16.6 mag assuming flat evolution (fading by 1 mag day(1)) at the 90% confidence level. If we further take into account the online terrestrial probability for each GW trigger, we find that no more than <68% of putative kilonovae could be brighter than 16.6 mag. Comparing to model grids, we find that some kilonovae must have Mej M, Xlan > 10(4), or > 30 degrees to be consistent with our limits. We look forward to searches in the fourth GW observing run; even 17 neutron star mergers with only 50% coverage to a depth of 16 mag would constrain the maximum fraction of bright kilonovae to <25%.


3. 
 Soumagnac, Maayane T., et al.
(författare)

SN 2018fif : The Explosion of a Large Red Supergiant Discovered in Its Infancy by the Zwicky Transient Facility
 2020

Ingår i: Astrophysical Journal.  : American Astronomical Society.  0004637X . 15384357. ; 902:1

Tidskriftsartikel (refereegranskat)abstract
 Highcadence transient surveys are able to capture supernovae closer to their first light than ever before. Applying analytical models to such early emission, we can constrain the progenitor stars' properties. In this paper, we present observations of SN 2018fif (ZTF 18abokyfk). The supernova was discovered close to first light and monitored by the Zwicky Transient Facility (ZTF) and the Neil Gehrels Swift Observatory. Early spectroscopic observations suggest that the progenitor of SN 2018fif was surrounded by relatively small amounts of circumstellar material compared to all previous cases. This particularity, coupled with the highcadence multipleband coverage, makes it a good candidate to investigate using shockcooling models. We employ the SOPRANOS code, an implementation of the model by Sapir & Waxman and its extension to early times by Morag et al. Compared with previous implementations, SOPRANOS has the advantage of including a careful account of the limited temporal validity domain of the shockcooling model as well as allowing usage of the entirety of the early UV data. We find that the progenitor of SN 2018fif was a large red supergiant with a radius of R = 744.0(128.0)(+183.0) Rcircle dot and an ejected mass of Mej = 9.3(5.8)(+0.4) Mcircle dot. Our model also gives information on the explosion epoch, the progenitor's inner structure, the shock velocity, and the extinction. The distribution of radii is doublepeaked, with smaller radii corresponding to lower values of the extinction, earlier recombination times, and a better match to the early UV data. If these correlations persist in future objects, denser spectroscopic monitoring constraining the time of recombination, as well as accurate UV observations (e.g., with ULTRASAT), will help break the extinction/radius degeneracy and independently determine both.

