Non-detection of Neutrinos from the BOAT: Improved Constraints on the Parameters of GRB 221009A

TL;DR

This paper reports a non-detection of neutrinos from the exceptionally bright GRB 221009A, providing improved constraints on its physical parameters and supporting high Lorentz factors in the burst's jet.

Contribution

It introduces the most accurate neutrino flux calculations for GRB 221009A and sets tighter limits on its physical parameters compared to previous studies.

Findings

No neutrinos detected from GRB 221009A

Constraints on Lorentz factor > 500, possibly > 1000

Improved limits on baryon loading and emission radius

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 non-thermal 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. Gamma-ray burst 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 (GBM) detected GRBs by a factor of two. 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 non-detection indicates a bulk Lorentz factor greater than 500 and possibly even 1000, consistent with other observations.