What did we learn from gamma-ray burst 080319B?

• Published in: Monthly notices of the Royal Astronomical Society. Letters 2008-11, Vol.391 (1), p.L19-L23
• Main Authors: Kumar, P., Panaitescu, A.
• Format: Article
• Language: English
• Subjects: AFTERGLOW; CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; COSMIC GAMMA BURSTS; DATA; DECAY; DISTANCE; EMISSION; ENERGY; gamma-rays: bursts; JETS; KINETIC ENERGY; PHOTONS; PLASMA; radiation mechanisms: non-thermal; RADIATIONS; shock waves; SYNCHROTRONS
• ISSN: 1745-3925; 1745-3933
• DOI: 10.1111/j.1745-3933.2008.00546.x

The optical and gamma-ray observations of GRB 080319B allow us to provide a broad-brush picture for this remarkable burst. The data indicate that the prompt optical and gamma-ray photons were possibly produced at the same location but by different radiation processes: synchrotron and synchrotron self-Compton, respectively (but we note that this interpretation of the gamma-ray data faces some difficulties). We find that the burst prompt optical emission was produced at a distance of 1016.3 cm by an ultrarelativistic source moving at Lorentz factor of ∼500. A straightforward inference is that about 10 times more energy must have been radiated at tens of GeV than that released at 1 MeV. Assuming that the GRB outflow was baryonic and the gamma-ray source was shock-heated plasma, the collimation-corrected kinetic energy of the jet powering GRB 080319B was larger than 1052.3 erg. The decay of the early afterglow optical emission (up to 1 ks) is too fast to be attributed to the reverse-shock crossing the GRB ejecta but is consistent with the expectations for the ‘large-angle’ emission released during the burst. The pure power-law decay of the optical afterglow flux from 1 ks to 10 d is most naturally identified with the (synchrotron) emission from the shock propagating into a wind-like medium. However, the X-ray afterglow requires a departure from the standard blast-wave model.