A detailed spectral study of GRB 041219A and its host galaxy

GRB041219A is one of the longest and brightest gamma-ray bursts (GRBs) ever observed. It was discovered by the INTEGRAL satellite, and thanks to a precursor happening about 300 s before the bulk of the burst, ground-based telescopes were able to catch the rarely observed prompt emission in the optical and in the near-infrared bands. Here we present the detailed analysis of its prompt gamma-ray emission, as observed with IBIS onboard INTEGRAL, and of the available X-ray afterglow data collected by X-Ray Telescope onboard Swift. We then present the late-time multiband near-infrared imaging data, collected at the Telescopio Nazionale Galileo (TNG) and the Canada-France-Hawaii Telescope (CFHT), that allowed us to identify the host galaxy of the GRB as an underluminous, irregular galaxy of~5 × 10⁹M_⊙at best-fitting redshift ofz= 0.31^+0.54_-0.26. We model the broad-band prompt optical to gamma-ray emission of GRB041219A within the internal shock model. We were able to reproduce the spectra and light curve invoking the synchrotron emission of relativistic electrons accelerated by a series of propagating shock waves inside a relativistic outflow. On the other hand, it is less easy to simultaneously reproduce the temporal and spectral properties of the infrared data.