Nondetection of Neutrinos from the BOAT: Improved Constraints on the Parameters of GRB 221009A

Abstract The IceCube neutrino observatory detects the diffuse astrophysical neutrino background with high significance, but the contribution of different classes of sources is not established. Because of their nonthermal spectrum, gamma-ray bursts (GRBs) are prime particle acceleration sites and one of the candidate classes for significant neutrino production. Exhaustive searches, based on stacking analysis of GRBs, however, could not establish the link between neutrinos and GRBs. GRB 221009A had the highest time integrated gamma-ray flux of any detected GRB so far. The total fluence exceeds the sum of all Fermi Gamma-ray Burst Monitor–detected GRBs by a factor of 2. Because it happened relatively nearby, it is one of the most favorable events for neutrino production from GRBs, yet no neutrinos were detected. We calculate neutrino fluxes for this GRB in the TeV–PeV range using the most accurate time-resolved spectral data covering the brightest intervals. We place limits on the physical parameters (Lorentz factor, baryon loading, or emission radius) of the burst that are better by a factor of 2 compared to previous limits. The neutrino nondetection indicates a bulk Lorentz factor greater than 500 and possibly even 800, consistent with other observations.