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.
The analysis of spectral lag between energy bands, which combines temporal and spectral analyses, can add strict constraints to gamma-ray burst (GRB) models. In previous studies, the lag analysis ...focused on the lags between channel 1 (25-57 keV) and channel 3 (115-320 keV) from the Burst and Transient Source Experiment (BATSE). In this Letter, we analyzed the cross-correlation average lags (including approximate uncertainties) between energy bands for two GRB samples: 19 events detected by Ginga and 109 events detected by BATSE. We paid special attention to the BATSE GRBs with known redshifts because there has been a reported connection between lag and luminosity. This extends our knowledge of spectral lags to lower energy ( approximately 2 keV). We found that lags between energy bands are small. The lag between the peak of approximately 50 keV photons and that of approximately 200 keV photons is approximately 0.08 s. The upper limit in the lag between approximately 9 and approximately 90 keV photons is approximately 0.5 s. Thus, there are not large shifts at low energy. We found that about 20% of GRBs have detectable lags between energy bands in the Ginga and BATSE samples. From the internal shock model, we found that there are three sources of time structure in GRB pulses: cooling, hydrodynamics, and angular effects. We argue that cooling is much too fast to account for our observed lags and that angular effects are independent of energy. Thus, only hydrodynamics can produce these lags. Perhaps the radiation process varies as the reverse shock moves through the shell.
We report on the spectral cross-calibration results of the Konus-Wind, the Suzaku/WAM, and the Swift/BAT instruments using simultaneously observed gamma-ray bursts (GRBs). This is the first attempt ...to use simultaneously observed GRBs as a spectral calibration source to understand systematic problems among the instruments. Based on these joint spectral fits, we find that (1) although a constant factor (a normalization factor) agrees within 20% among the instruments, the BAT constant factor shows a systematically smaller value by 10%–20% compared to that of Konus-Wind, (2) there is a systematic trend that the low-energy photon index becomes steeper by 0.1–0.2 and
$E_{\rm peak}$
becomes systematically higher by 10%–20% when including the BAT data in the joint fits, and (3) the high-energy photon index agrees within 0.2 among the instruments. Our results show that cross-calibration based on joint spectral analysis is an important step to understanding the instrumental effects that could be affecting the scientific results from the GRB prompt emission data.
The Wide-field X-ray Monitor (WXM) is one of the scientific instruments carried on the High Energy Transient Explorer 2 (HETE-2) satellite launched on 2000 October 9. HETE-2 is an international ...mission consisting of a small satellite dedicated to provide broad-band observations and accurate localizations of gamma-ray bursts (GRBs). A unique feature of this mission is its capability to determine and transmit GRB coordinates in almost real-time through the burst alert network. The WXM consists of three elements: four identical Xe-filled one-dimensional position-sensitive proportional counters, two sets of one-dimensional coded apertures, and the main electronics. The WXM counters are sensitive to X-rays between 2 keV and 25 keV within a field-of-view of about 1.5 sr, with a total detector area of about
$350 \,\mathrm{cm}^2$
. The in-flight triggering and localization capability can produce a real-time GRB location of several to 30 arcmin accuracy, with a limiting sensitivity of
$10^{-7} \,\mathrm{erg} \,\mathrm{cm}^{-2}$
. In this report, the details of the mechanical structure, electronics, on-board software, ground and in-flight calibration, and in-flight performance of the WXM are discussed.
HETE-2 Observations of the X-Ray Flash XRF 040916 Arimoto, Makoto; Kawai, Nobuyuki; Suzuki, Motoko ...
Publications of the Astronomical Society of Japan,
06/2007, Volume:
59, Issue:
3
Journal Article
Peer reviewed
Open access
A long X-ray flash was detected and localized by instruments aboard the High Energy Transient Explorer II (HETE-2) at 00:03:30 UT on 2004 September 16. The position was reported to the GRB ...Coordinates Network (GCN) approximately 2 hours after the burst. This burst consisted of two peaks separated by
$\sim 200$
s, with durations of about 110 s and 60 s. We analyzed the energy spectra of the 1st and 2nd peaks observed with the Wide Field X-Ray Monitor (WXM) and the French Gamma Telescope (FREGATE). We discuss the origin of the 2nd peak in terms of the flux variabilities and timescales. We find that it is most likely to be part of prompt emission, and is explained by a long-acting engine model. This feature is similar to some bright X-ray flares detected in the early afterglow phase of bursts observed by the Swift satellite.
An Optically Dark GRB Observed by HETE-2: GRB 051022 Nakagawa, Yujin E.; Yoshida, Atsumasa; Sugita, Satoshi ...
Publications of the Astronomical Society of Japan,
08/2006, Volume:
58, Issue:
4
Journal Article
Peer reviewed
Open access
GRB 051022 was detected at 13:07:58 on 2005 October 22 UT by HETE-2. The location of GRB 051022 was determined immediately by the flight localization system. This burst contained multiple pulses, and ...had a rather long duration of about 190 s. The detections of candidate X-ray and radio afterglows were reported, whereas no optical afterglow was found. Optical spectroscopic observations of the host galaxy revealed a redshift of
$z = 0.8$
. Using data derived by a HETE-2 observation of the prompt emission, we found absorption of
$N_{\mathrm{H}} = (8.8_{-2.9}^{+3.1}) \times 10^{22} \,\mathrm{cm}^{-2}$
and visual extinction of
$A_{V} = 49_{-16}^{+17}$
mag in the host galaxy. If this is the case, no detection of any optical transient would be quite reasonable. The absorption derived by Swift XRT observations of the afterglow is fully consistent with those obtained from an early HETE-2 observation of the prompt emission. Our analysis implies an interpretation that the absorbing medium may be outside the external shock at
$R \sim 10^{16} \,\mathrm{cm}$
, which could be a dusty molecular cloud.
GRB041006 was detected by HETE-2 on 2004 October 06. The light curves in four different energy bands display different features. At higher energy bands several peaks are seen in the light curve, ...while at lower energy bands a single broader bump dominates. It is expected that these different features are the result of a mixture of several components, each of which has different energetics and variability. We analyzed the time-resolved spectra, which were resolved into several components. These components can be classified into two distinct classes. One is a component that has an exponential decay of
$E_{\rm p}$
with a characteristic timescale shorter than
$\sim\;$
30 s; its spectrum is well represented by a broken power-law function, which is frequently observed in many prompt GRB emissions, so it should have an internal-shock origin. Another is a component whose
$E_{\rm p}$
is almost unchanged with a characteristic timescale longer than
$\sim\;$
60 s, and shows a very soft emission and slower variability. The spectrum is characterized by either a broken power law or a black-body spectrum. By assuming that the soft component is a thermal emission, the radiation radius is initially
$4.4 \times 10^{6}$
km, which is a typical radius of a blue supergiant, and its expansion velocity is
$2.4 \times 10^{5}$
km s
$^{-1}$
in the source frame.
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