GRB 221009A: The BOAT Burns, Eric; Svinkin, Dmitry; Fenimore, Edward ...
Astrophysical journal. Letters,
03/2023, Volume:
946, Issue:
1
Journal Article
Peer reviewed
Open access
Abstract GRB 221009A has been referred to as the brightest of all time (BOAT). We investigate the veracity of this statement by comparing it with a half century of prompt gamma-ray burst ...observations. This burst is the brightest ever detected by the measures of peak flux and fluence. Unexpectedly, GRB 221009A has the highest isotropic-equivalent total energy ever identified, while the peak luminosity is at the ∼99th percentile of the known distribution. We explore how such a burst can be powered and discuss potential implications for ultralong and high-redshift gamma-ray bursts. By geometric extrapolation of the total fluence and peak flux distributions, GRB 221009A appears to be a once-in-10,000-year event. Thus, it is almost certainly not the BOAT over all of cosmic history; it may be the brightest gamma-ray burst since human civilization began.
We report on a search for high-energy counterparts to fast radio bursts (FRBs) with the Fermi Gamma-ray Burst Monitor, Fermi Large Area Telescope, and the Neil Gehrels Swift Observatory Burst Alert ...Telescope. We find no significant associations for any of the 23 FRBs in our sample, but report upper limits to the high-energy fluence for each on timescales of 0.1, 1, 10, and 100 s. We report lower limits on the ratio of the radio to high-energy fluence, fr/fγ, for timescales of 0.1 and 100 s. We discuss the implications of our non-detections on various proposed progenitor models for FRBs, including analogs of giant pulses from the Crab pulsar and hyperflares from magnetars. This work demonstrates the utility of analyses of high-energy data for FRBs in tracking down the nature of these elusive sources.
Spectra of broad-lined Type Ic supernovae (SNeIc-BL), the only kind of SN observed at the locations of long-duration gamma-ray bursts (LGRBs), exhibit wide features indicative of high ejecta ...velocities (~0.1c). We study the host galaxies of a sample of 245 low-redshift (z < 0.2) core-collapse SNe, including 17 SNeIc-BL, discovered by galaxy-untargeted searches, and 15 optically luminous and dust-obscured z < 1.2 LGRBs. We show that, in comparison with Sloan Digital Sky Survey galaxies having similar stellar masses, the hosts of low-redshift SNe Ic-BL and z < 1.2 LGRBs have high stellar mass and star formation rate densities. Core-collapse SNe having typical ejecta velocities, in contrast, show no preference for such galaxies. Moreover, we find that the hosts of SNe Ic-BL, unlike those of SNe Ib/Ic and SNe II, exhibit high gas velocity dispersions for their stellar masses. The patterns likely reflect variations among star-forming environments and suggest that LGRBs can be used as probes of conditions in high-redshift galaxies. They may be caused by efficient formation of massive binary progenitor systems in densely star-forming regions, or, less probably, a higher fraction of stars created with the initial masses required for an SN Ic-BL or LGRB. Finally, we show that the preference of SNe Ic-BL and LGRBs for galaxies with high stellar mass and star formation rate densities cannot be attributed to a preference for low metal abundances but must reflect the influence of a separate environmental factor.
We present multiwavelength modeling of the afterglow from the long γ-ray 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 γ-ray frequencies. These observations range from ∼0.1 days to >1000 days, thus making this event extremely well suited to such modeling. In this work we compare top-hat and Gaussian jet structure types in order to find best-fit values for the GRB jet collimation angle, viewing angle, and other physical parameters. We find that a Gaussian-shaped jet is preferred (2.7 -5.3 ) over the traditional top-hat model. Our estimate for the opening angle of the burst ranges from 1 26 to 3 90, depending on jet-shape 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 ∼1053 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.
Abstract
We perform a detailed analysis of broad pulses in bright gamma-ray bursts (GRBs) to understand the evolution of GRB broad pulses. Using the temporal and spectral properties, we test the ...high-latitude emission (HLE) scenario in the decaying phase of broad pulses. The HLE originates from the curvature effect of a relativistic spherical jet, where higher-latitude photons are delayed and softer than the observer’s line-of-sight emission. The signature of HLE has not yet been identified undisputedly during the prompt emission of GRBs. The HLE theory predicts a specific relation,
F
ν
,
E
p
∝
E
p
2
, between the peak energy
E
p
in
ν
F
ν
spectra and the spectral flux
F
ν
measured at
E
p
,
F
ν
,
E
p
. We search for evidence of this relation in 2157 GRBs detected by the Gamma-ray Burst Monitor on board the Fermi Gamma-ray Space Telescope from 2008 to 2017. After imposing unbiased selection criteria in order to minimize contamination in a signal by background and overlaps of pulses, we build a sample of 32 broad pulses in 32 GRBs. We perform a time-resolved spectral analysis on each of these 32 broad pulses and find that the evolution of 18 pulses (56%) is clearly consistent with the HLE relation. For the 18 broad pulses, the exponent
δ
in the relation of
F
ν
,
E
p
∝
E
p
δ
is distributed as a Gaussian function with a median and width of 1.99 and 0.34, respectively. This result provides a constraint on the emission radius of GRBs with the HLE signature.
Abstract One of the difficulties in nailing down the physical mechanism of gamma-ray bursts (GRBs) comes from the fact that there has been no clear observational evidence on how far from the central ...engine the prompt gamma rays of GRBs are emitted. Here we present a simple study addressing this question by making use of the “high-latitude emission” (HLE). We show that our detailed numerical modeling exhibits a clear signature of HLE in the decaying phase of “broad pulses” of GRBs. We show that the HLE can emerge as a prominent spectral break in F ν spectra and dominate the peak of ν F ν spectra even while the “line-of-sight emission” (LoSE) is still ongoing. This finding provides a new view of HLE emergence since it has been believed so far that the HLE can show up and dominate the spectra only after the LoSE is turned off. We remark, however, that this “HLE break” can be hidden in some broad pulses, depending on the proximity between the peak energies of the LoSE and the HLE. Therefore, this new picture of HLE emergence explains both the detection and nondetection of HLE signature in observations of broad pulses. Also, we present three examples of Fermi Gamma-ray Burst Monitor GRBs with broad pulses that exhibit the HLE signature. We show that their gamma-ray-emitting region should be located at ∼10 16 cm from the central engine, which places a constraint on the GRB models.
I investigate the origin of the observed correlation between a gamma-ray burst's (GRB's) nuF sub(nu) spectral peak E sub(pk) and its isotropic equivalent energy E sub(iso) through the use of a ...population synthesis code to model the prompt gamma-ray emission from GRBs. By using prescriptions for the distribution of prompt spectral parameters as well as the population's luminosity function and comoving rate density, I generate a simulated population of GRBs and examine how bursts of varying spectral properties and redshift would appear to a gamma-ray detector here on Earth. I find that a strong observed correlation can be produced between the source frame E sub(pk) and E sub(iso) for the detected population despite the existence of only a weak and broad correlation in the original simulated population. The energy dependance of a gamma-ray detector's flux-limited detection threshold acts to produce a correlation between the source frame E sub(pk) and E sub(iso) for low-luminosity GRBs, producing the left boundary of the observed correlation. Conversely, very luminous GRBs are found at higher redshifts than their low-luminosity counterparts due to the standard Malquest bias, causing bursts in the low E sub(pk), high E sub(iso) regime to go undetected because their E sub(pk) values would be redshifted to energies at which most gamma-ray detectors become less sensitive. I argue that it is this previously unexamined effect which produces the right boundary of the observed correlation. Therefore, the origin of the observed correlation is a complex combination of the instrument's detection threshold, the intrinsic cutoff in the GRB luminosity function, and the broad range of redshifts over which GRBs are detected. Although the GRB model presented here is a very simplified representation of the complex nature of GRBs, these simulations serve to demonstrate how selection effects caused by a combination of instrumental sensitivity and the cosmological nature of an astrophysical population can act to produce an artificially strong correlation between observed properties.
We examine the effects of time dilation on the temporal profiles of gamma-ray burst (GRB) pulses. By using prescriptions for the shape and evolution of prompt gamma-ray spectra, we can generate a ...simulated population of single-pulsed GRBs at a variety of redshifts and observe how their light curves would appear to a gamma-ray detector here on Earth. We find that the observer frame duration of individual pulses does not increase with redshift as 1 + z, which one would expect from cosmological expansion. This time dilation is masked by an opposite and often stronger effect: with increasing redshift and decreasing signal-to-noise ratio only the brightest portion of the light curve can be detected. The results of our simulation are consistent with the fact that the simple time dilation of GRB light curves has not materialized in either the Swift or Fermi detected GRBs with known redshift. We show that the measured durations and associated E sub(iso) estimates for GRBs detected near the instrument's detection threshold should be considered lower limits to the true values. Furthermore, we conclude that attempts at distinguishing between long and short GRBs, at even moderate redshifts, cannot be done based on a burst's temporal properties alone.
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