Implication of Jet Physics from MeV Line Emission of GRB 221009A

Abstract

Ultrarelativistic jets are believed to play an important role in producing prompt emission and afterglow of gamma-ray bursts (GRBs), but the nature of the jet is poorly known owing to the lack of decisive features observed in the prompt emission. The discovery of an emission line evolving from about 37 to 6 MeV in the brightest-of-all-time GRB 221009A provides an unprecedented opportunity to probe GRB jet physics. The time evolution of the central energy of the line with power-law index $-1$ is naturally explained by the high-latitude curvature effect. Under the assumption that the line emission is generated in the prompt emission by $e^{\pm }$ pair production, cooling, and annihilation in the jet, we can strictly constrain jet physics with observed line emission properties. We find that the radius of the emission region is $r\gtrsim 10^{16}$ cm. The narrow line width of $\sim 10\%$ requires that the line emission occurs within $\sim 10\%$ of the dynamical time, which further implies short timescales of pair cooling to the nonrelativistic state and pair annihilation, as well as a slightly clumpy emission region. If the jet's Lorentz factor is $\Gamma \gtrsim 400$, the fast cooling requirement needs an energy density of magnetic field in the jet much larger than that of prompt gamma rays, i.e., a magnetically dominated jet. The temporal behavior of line flux suggests some angle dependence of line emission. We also discuss the difficulties of other scenarios for the observed emission line.

arXiv comment8 pages, 3 figures. Published in ApJL

References in corpus (27)

• Unsteady Outflow Models for Cosmological Gamma-Ray Bursts
• The Internal-Collision-Induced Magnetic Reconnection and Turbulence (ICMART) Model of Gamma-Ray Bursts
• Dissipative Photosphere Models of Gamma-ray Bursts and X-ray Flashes
• Steep Slopes and Preferred Breaks in GRB Spectra: the Role of Photospheres and Comptonization
• Gamma-ray bursts from internal shocks in a relativistic wind: temporal and spectral properties
• Lower Limits on Lorentz Factors in Gamma Ray Bursts
• Afterglow Emission from Naked Gamma-Ray Bursts
• Poynting Jets from Black Holes and Cosmological Gamma-Ray Bursts
• The observable effects of a photospheric component on GRB's and XRF's prompt emission spectrum
• A tera-electronvolt afterglow from a narrow jet in an extremely bright gamma-ray burst 221009A
• Evidence of an initially magnetically dominated outflow in GRB 080916C
• Gamma-Ray Burst Afterglows: Effects of Radiative Corrections and Nonuniformity of the Surrounding Medium
• GRB 221009A, The BOAT
• Fermi-GBM Discovery of GRB 221009A: An Extraordinarily Bright GRB from Onset to Afterglow
• Prompt GRB spectra: detailed calculations and the effect of pair production
• The Observed Size and Shape of GRB Afterglow
• Properties of the extremely energetic GRB~221009A from Konus-WIND and SRG/ART-XC observations
• Emission Spectra from Internal Shocks in Gamma-Ray-Burst Sources
• Structure of Gamma-Ray Burst jets: intrinsic versus apparent properties
• Prompt GeV Emission from Residual Collisions in GRB Outflows: Evidence from Fermi Observations of GRB 080916c
• Constraints on the Model of Gamma-ray Bursts and Implications from GRB 221009A: GeV gamma rays v.s. High-energy Neutrinos
• Observation of spectral lines in the exceptional GRB 221009A
• The elementary spike produced by a pure $e^{+}{e}^{-}$ pair-electromagnetic pulse from a Black Hole: The PEM Pulse
• Closure Relations for Electron-Positron Pair-Signatures in Gamma-Ray Bursts
• Relation between the keV-MeV and TeV emission of GRB 221009A and its implications
• Implication of GRB 221009A: Can TeV Emission Come from the GRB Prompt Phase?
• A Novel Model for the MeV Emission Line in GRB 221009A