Kavli Affiliate: Dheeraj R. Pasham
| First 5 Authors: Maia A. Williams, Jamie A. Kennea, S. Dichiara, Kohei Kobayashi, Wataru B. Iwakiri
| Summary:
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.
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