Detection of 2 MeV spectral bump and ~40 MeV emission line from GRB 221009A

Abstract

Gamma-ray bursts (GRBs) are the most energetic transients in the Universe, but prompt MeV--sub-GeV observations remain challenging with current gamma-ray observatories. Here, using unsaturated HEPP-H measurements on board CSES-01 and cross-calibrating with likewise unsaturated GECAM-C data, we reconstruct the continuous spectral evolution of GRB 221009A over 2--255 MeV. We identify an unusual spectral bump at $\sim$2 MeV in the first light-curve peak. We also confirm a narrow emission line whose energy decreases from $\sim$40 MeV following a $t^{-1}$ evolution, and whose flux shows a ``rise-then-fall'' profile, implying weak emission from the central jet. These findings hint that a magnetically dominated, central-empty jet exists in the BOAT.

arXiv comment40 pages; accepted for publication in The Astrophysical Journal Letters

References in corpus (17)

• The Large Area Telescope on the Fermi Gamma-ray Space Telescope Mission
• The Fermi Gamma-Ray Burst Monitor
• Steep Slopes and Preferred Breaks in GRB Spectra: the Role of Photospheres and Comptonization
• Afterglow Emission from Naked Gamma-Ray Bursts
• A Comprehensive Analysis of Fermi Gamma-Ray Burst Data. I. Spectral Components and Their Possible Physical Origins of LAT/GBM GRBs
• A tera-electronvolt afterglow from a narrow jet in an extremely bright gamma-ray burst 221009A
• A theory of photospheric emission from relativistic, collimated outflows
• GRB 221009A, The BOAT
• Fermi-GBM Discovery of GRB 221009A: An Extraordinarily Bright GRB from Onset to Afterglow
• A Theory of Mulicolor Black Body Emission from Relativistically Expanding Plasmas
• GRB 221009A: Discovery of an Exceptionally Rare Nearby and Energetic Gamma-Ray Burst
• Consistency with synchrotron emission in the bright GRB 160625B observed by Fermi
• Observation of spectral lines in the exceptional GRB 221009A
• The brightest GRB ever detected: GRB 221009A as a highly luminous event at z = 0.151
• Implication of Jet Physics from MeV Line Emission of GRB 221009A
• Brightest GRB flare observed in GRB 221009A: bridge the last gap between flare and prompt emission in GRB
• A Method for Gamma-Ray Energy Spectrum Inversion and Correction