GRB 221009A: A Light Dark Matter Burst or an Extremely Bright Inverse Compton Component?

Abstract

Gamma-ray bursts (GRBs) have been considered as potential very high energy photon emitters due to the large amount of energy released as well as the strong magnetic fields involved in their jets. However, the detection of teraelectronvolt photons is not expected from bursts beyond a redshift of z ≳ 0.1, due to their attenuation with the extragalactic background light (EBL). For these reasons, the recent observation of photons with energies of 18 and 251 TeV from GRB 221009A (z = 0.151) last 2022 October 9 has challenged what we know about the teraelectronvolt-emission mechanisms and the extragalactic background. In order to explain the teraelectronvolt observations, recent works exploring candidates of dark matter have started to appear. In this paper, we discuss the required conditions and limitations within the most plausible scenario, synchrotron self-Compton radiation in the GRB afterglow, to interpret the one 18 TeV photon observation besides the EBL. To avoid the Klein–Nishina effect, we find an improbable value of the microphysical magnetic parameter below 10−6 for a circumburst medium value >1 cm−3 (expected in the collapsar scenario). Therefore, we explore possible scenarios in terms of axion-like particles (ALPs) and dark photon mechanisms to interpret this highly energetic photon and we discuss the implications in the GRB energetics. We find that the ALPs and dark photon scenarios can explain the 18 teraelectronvolt photon but not the 251 teraelectronvolt photon.