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

We report on the unusually bright long gamma-ray burst (GRB) 221009A observed by the Neil Gehrels Swift Observatory (Swift), Monitor of All-sky X-ray Image (MAXI), and Neutron Star Interior Composition Explorer Mission (NICER). Due to its brightness and relative proximity (z = 0.151), our combined observations of the GRB 221009A afterglow span over about 70 days after the Fermi Gamma-ray Burst Monitor trigger. We present analysis of light curves at UV-optical and X-ray wavelengths. From the prominent dust scattering echo, we determine the distances to interstellar dust concentrations along the line of sight to the burst. We discuss how the brightness of GRB 221009A compares to the sample of GRBs observed by Swift and find that GRB 221009A is an extremely rare event, with similar GRBs estimated to occur about once every 1000 years.