The Swift Gamma-Ray Burst Explorer performed its first autonomous, X-ray follow-up to a newly detected GRB on 2005 January 17, within 193 s of the burst trigger by the Swift Burst Alert Telescope. ...While the burst was still in progress, the X-Ray Telescope (XRT) obtained a position and an image for an uncataloged X-ray source simultaneously with the gamma-ray observation. The XRT observed flux during the prompt emission was 1.1 x 10 super(-8) ergs cm super(-2) s super(-1) in the 0.5-10 keV energy band. The emission in the X-ray band decreased by 3 orders of magnitude within 700 s, following the prompt emission. This is found to be consistent with the gamma-ray decay when extrapolated into the XRT energy band. During the following 6.3 hr, the XRT observed the afterglow in an automated sequence for an additional 947 s, until the burst became fully obscured by the Earth limb. A faint, extremely slowly decaying afterglow, a = -0.21, was detected. Finally, a break in the light curve occurred and the flux decayed with a < -1.2. The X-ray position triggered many follow-up observations: no optical afterglow could be confirmed, although a candidate was identified 3" from the XRT position.
The detection of gravitational waves from a binary neutron star merger by Advanced LIGO and Advanced Virgo (GW170817), along with the discovery of the electromagnetic counterparts of this ...gravitational wave event, ushered in a new era of multimessenger astronomy, providing the first direct evidence that BNS mergers are progenitors of short gamma-ray bursts (GRBs). Such events may also produce very-high-energy (VHE, > 100GeV) photons which have yet to be detected in coincidence with a gravitational wave signal. The Cherenkov Telescope Array (CTA) is a next-generation VHE observatory which aims to be indispensable in this search, with an unparalleled sensitivity and ability to slew anywhere on the sky within a few tens of seconds. New observing modes and follow-up strategies are being developed for CTA to rapidly cover localization areas of gravitational wave events that are typically larger than the CTA field of view. This work will evaluate and provide estimations on the expected number of of gravitational wave events that will be observable with CTA, considering both on- and off-axis emission. In addition, we will present and discuss the prospects of potential follow-up strategies with CTA.
We report the discovery of the unusually bright long-duration gamma-ray burst (GRB), GRB 221009A, as observed by the Neil Gehrels Swift Observatory (Swift), Monitor of All-sky X-ray Image (MAXI), and ...Neutron Star Interior Composition Explorer Mission (NICER). This energetic GRB was located relatively nearby (z = 0.151), allowing for sustained observations of the afterglow. The large X-ray luminosity and low Galactic latitude (b = 4.3 degrees) make GRB 221009A a powerful probe of dust in the Milky Way. Using echo tomography we map the line-of-sight dust distribution and find evidence for significant column densities at large distances (~> 10kpc). We present analysis of the light curves and spectra at X-ray and UV/optical wavelengths, and find that the X-ray afterglow of GRB 221009A is more than an order of magnitude brighter at T0 + 4.5 ks than any previous GRB observed by Swift. In its rest frame GRB 221009A is at the high end of the afterglow luminosity distribution, but not uniquely so. In a simulation of randomly generated bursts, only 1 in 10^4 long GRBs were as energetic as GRB 221009A; such a large E_gamma,iso implies a narrow jet structure, but the afterglow light curve is inconsistent with simple top-hat jet models. Using the sample of Swift GRBs with redshifts, we estimate that GRBs as energetic and nearby as GRB 221009A occur at a rate of ~<1 per 1000 yr - making this a truly remarkable opportunity unlikely to be repeated in our lifetime.
Astrophys.J.653:468-473,2006 We report the best evidence to date of a jet break in a short Gamma-Ray Burst
(GRB) afterglow, using Chandra and Swift XRT observations of the X-ray
afterglow of GRB ...051221A. The combined X-ray light curve, which has three
breaks, is similar to those commonly observed in Swift observations of long
GRBs. A flat segment of the light curve at ~0.1 days after the burst represents
the first clear case of strong energy injection in the external shock of a
short GRB afterglow. The last break occurs at ~4 days post-burst and breaks to
a power-law decay index of ~2. We interpret this as a jet break, with important
implications for models of short GRBs, since it requires collimation of the
afterglow into a jet with an initial opening angle ~4-8 degrees and implies a
total jet kinetic energy of E_jet ~(1-5) x 10^{49} erg. Combined with the lack
of a jet break in GRB 050724, this suggests a wide range in jet collimation in
short GRBs, with at least some having collimation similar to that found in long
GRBs, though with significantly lower jet energies.
We report the best evidence to date of a jet break in a short Gamma-Ray Burst (GRB) afterglow, using Chandra and Swift XRT observations of the X-ray afterglow of GRB 051221A. The combined X-ray light ...curve, which has three breaks, is similar to those commonly observed in Swift observations of long GRBs. A flat segment of the light curve at ~0.1 days after the burst represents the first clear case of strong energy injection in the external shock of a short GRB afterglow. The last break occurs at ~4 days post-burst and breaks to a power-law decay index of ~2. We interpret this as a jet break, with important implications for models of short GRBs, since it requires collimation of the afterglow into a jet with an initial opening angle ~4-8 degrees and implies a total jet kinetic energy of E_jet ~(1-5) x 10^{49} erg. Combined with the lack of a jet break in GRB 050724, this suggests a wide range in jet collimation in short GRBs, with at least some having collimation similar to that found in long GRBs, though with significantly lower jet energies.
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