Deciphering the ~18 TeV photons from GRB 221009A

Sarira Sahu, B. Medina-Carrillo, G. Sánchez-Colón, Subhash Rajpoot

Submitted on 8 November 2022


On 9 October, 2022, an extremely powerful gamma-ray burst, GRB 221009A, was detected by several instruments. Despite being obstructed by the Milky Way galaxy, its afterglow outburst outshone all other GRBs seen before. LHAASO detected several thousands very-high energy photons extending up to 18 TeV. Detection of such energetic photons are unexpected due to the large opacity of the Universe. It is possible that in the afterglow epoch the intrinsic very high-energy photon flux from the source might have increased manifolds, which could compensate the attenuation by pair-production with the extragalactic background light. We propose such a scenario and show that very high-energy photons can be observed on the Earth from the interaction of very-high energy protons with the seed synchrotron photons in the external forward shock region of the GRB jet.


Comment: 7 pages, 2 figures

Subjects: Astrophysics - High Energy Astrophysical Phenomena; High Energy Physics - Phenomenology


Using the effective area of the detector LHAASO-WCDA the VHE Spectrum for GRB 221009A is given for different values of the spectral index $\delta$, by fixing $N_{\gamma}=5500$. The intrinsic flux for each $\delta$ also shown. The LHAASO sensitivity curve for with 2000 s exposure is also shown. The vertical line corresponds to 18 TeV photon energy. The shaded region is $\pm 50\%$ relative energy resolution of LHAASO-WCDA for $E_{\gamma}\simeq 18$ TeV.