Constrains on the physics of the prompt emission from a distant and energetic gamma-ray burst GRB 220101A

Abstract

The emission region of $\gamma$-ray bursts (GRBs) is poorly constrained. The uncertainty on the size of the dissipation site spans over 4 orders of magnitude ($10^{12}-10^{17}$ cm) depending on the unknown energy composition of the GRB jets. The joint multi-band analysis from soft X-rays to high energies (up to $\sim$ 1 GeV) of one of the most energetic and distant GRB 220101A (z = 4.618) allows us for an accurate distinction between prompt and early afterglow emissions. The enormous amount of energy released by GRB 220101A (${\mathrm{E}}_{\mathrm{iso}}\approx 3\times 10^{54}$ erg) and the spectral cutoff at ${\mathrm{E}}_{\mathrm{cutoff}}=85_{-26}^{+16}$ MeV observed in the prompt emission spectrum constrains the parameter space of GRB dissipation site. We put stringent constraints on the prompt emission site, requiring $700<{\mathrm{\Gamma }}_0<1160$ and ${\mathrm{R}}_{\gamma }\sim 4.5\times 10^{13}$ cm. Our findings further highlights the difficulty of finding a simple self consistent picture in the electron-synchrotron scenario, favoring instead a proton-synchrotron model, which is also consistent with the observed spectral shape. Deeper measurements of the time variability of GRBs together with accurate high-energy observations (MeV-GeV) would unveil the nature of the prompt emission.

16 pages, 7 figures. Accepted for ApJ publication

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Cited by in corpus (2)

• Insights into the physics of GRBs from the high-energy extension of their prompt emission spectra
• An optical-ultraviolet flare with absolute AB magnitude of -39.4 detected in GRB 220101A