GRB 221009A: Discovery of an Exceptionally Rare Nearby and Energetic Gamma-Ray Burst

TL;DR

The paper reports the discovery and detailed analysis of GRB 221009A, an exceptionally bright, nearby, and energetic gamma-ray burst, providing insights into its properties, dust environment, and rarity.

Contribution

It presents the first detailed multi-wavelength observations of such an energetic and nearby GRB, including dust mapping and challenges to simple jet models.

Findings

GRB 221009A is over an order of magnitude brighter than previous Swift GRBs.

Such energetic and nearby GRBs occur roughly once every 1000 years.

The afterglow data challenge simple top-hat jet models.

Abstract

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.