SSC Radiation in the ICMART Model: Spectral Simulations and Application to the Record-Breaking GRB 221009A

TL;DR

This study models the SSC spectrum within the ICMART framework, revealing how key parameters influence GRB spectral features and applying the model to explain the exceptional GRB 221009A observations.

Contribution

It introduces detailed spectral simulations of the SSC component in the ICMART model and applies these to interpret the record-breaking GRB 221009A.

Findings

Spectral features depend on magnetization and Y parameter.

Positive correlation between Y and magnetization contrasts with shock models.

Model reproduces GRB 221009A's broadband spectrum with low magnetization.

Abstract

This paper presents simulations of the synchrotron self-Compton (SSC) spectrum within the Internal-Collision-induced Magnetic Reconnection and Turbulence (ICMART) model. We investigate how key parameters like the magnetization $\sigma_0$ shape the broadband spectral energy distribution by regulating the electron distribution and magnetic field strength. The overall spectrum typically comprises two components: synchrotron radiation peaking at $E_{\rm p}$ with a low-energy spectral index $\alpha$ between -1 and -1.5, and an SSC component peaking at $E_{\rm ssc}$. At high energies, Klein-Nishina suppression causes an exponential cutoff. The flux ratio Y between these components is critical: when Y is small, the SSC peak can be suppressed. Spectral features of the synchrotron component reveal the underlying physical conditions: harder spectra with $\alpha\sim-1$ indicate a large Y parameter and strong KN suppression. We find a positive correlation between Y and $\sigma_0$, contrasting with internal shock model predictions. Applied to GRB 221009A, our model suggests $\sigma_0\leq20$ can reproduce the MeV-TeV observations. This study underscores the value of combined MeV-TeV observations in probing GRB emission mechanisms.