Kavli Affiliate: Nicola Omodei
| First 5 Authors: Saikat Das, Soebur Razzaque, Nestor Mirabal, Nicola Omodei, Kohta Murase
| Summary:
We search for possible GeV-TeV gamma-ray imprints of ultrahigh-energy (UHE;
$gtrsim 0.1$ EeV) cosmic ray (CR) acceleration in the large-scale structures
surrounding the brightest gamma-ray burst (GRB) explosion, GRB 221009A. Using
1.25 years of post-event Fermi Large Area Telescope (LAT) data, we construct a
1 GeV – 1 TeV test-statistic (TS) map within 15 Mpc of the burst. We identify
two peaks in the TS map with TS $geq 9$. The most significant peak,
J1911.8+2044, exhibits gamma-ray emission in pre-burst LAT data. The other
peak, J1913.2+1901, coincides with a 664.6 GeV photon recorded $sim191.9$ days
after the GRB trigger and located at about $0.75^{circ}$ from the GRB
localization. The per-photon 95% containment angle for the LAT is about
$0.25^{circ}$ in the 100 GeV – 1 TeV energy range. We explore two possible
origins for the $gamma$-ray emission: (1) UHECRs from GRB 221009A propagating
through a magnetized cosmological volume in its vicinity, and (2) UHE or
very-high-energy (VHE; $gtrsim 100$ GeV) $gamma$-ray emission from GRB
221009A, propagating in the same volume. In both cases, electromagnetic cascade
emission is induced in the structured region embedding the burst. If any TS
features are related to large-scale imprints induced by cosmic rays, it might
be further evidence that GRB 221009A accelerated UHECRs. However, our results
show that alternative scenarios without invoking UHECRs cannot be ruled out,
and the observed high-energy photon could be unrelated to GRB 221009A.
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