A Cosmological Fireball with Sixteen-Percent Gamma-Ray Radiative Efficiency

Abstract

Gamma-ray bursts (GRBs) are the most powerful explosions in the universe. How efficiently the jet converts its energy to radiation is a long-standing problem and it is poorly constrained. The standard model invokes a relativistic fireball with a bright photosphere emission component. A definitive diagnosis of GRB radiation components and measurement of GRB radiative efficiency require prompt emission and afterglow data with high-resolution and wide-band coverage in time and energy. Here we report a comprehensive temporal and spectral analysis of the TeV-emitting bright GRB 190114C. Its fluence is one of the highest of all GRBs detected so far, which allows us to perform a high-resolution study of the prompt emission spectral properties and their temporal evolution down to a timescale of about 0.1 s. We observe that each of the initial pulses has a thermal component contributing $\sim 20\%$ of the total energy, the corresponding temperature and the inferred Lorentz factor of the photosphere evolve following broken power-law shapes. From the observation of the non-thermal spectra and the light curve, the onset of afterglow corresponding to the deceleration of the fireball is considered at $\sim 6$~s. By incorporating the thermal and the non-thermal observations, as well as the photosphere and the synchrotron radiative mechanisms, we can directly derive the fireball energy budget with little dependence on hypothetical parameters and to measure a $\sim 16\%$ radiative efficiency for this GRB. With the fireball energy budget derived, the afterglow microphysics parameters can also be constrained directly from the data.

27 pages, 8 figures (including 14 panels), 6 tables, accepted for publication in The Astrophysical Journal Letters

References in corpus (19)

• An online repository of Swift/XRT light curves of GRBs
• Teraelectronvolt emission from the $\gamma$-ray burst GRB 190114C
• GRB Radiative Efficiencies Derived from the Swift Data: GRBs vs. XRFs, Long vs. Short
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• The SOFIA Massive (SOMA) Star Formation Survey. II. High Luminosity Protostars
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• The supernova of the MAGIC GRB190114C
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Cited by in corpus (5)

• Multipolar Electromagnetic Emission of Newborn Magnetar
• Probing gamma-ray bursts observed at very high energies through their afterglow
• Time-averaging Polarimetric and Spectral Properties of Gamma-Ray Bursts
• GRB 190114C: Fireball Energy Budget and Radiative Efficiency Revisited
• A generalized method to measure the Lorentz factor from gamma-ray burst photospheric emission