2013A&A...557L..18D

Gamma-ray bursts (GRBs) are the most luminous explosions that we can witness in the Universe. Studying the most extreme cases of these phenomena allows us to constrain the limits for the progenitor models. In this Letter, we study the prompt emission, afterglow, and host galaxy of GRB120624B, one of the brightest GRBs detected by Fermi, to derive the energetics of the event and characterise the host galaxy in which it was produced. Following the high-energy detection we conducted a multi-wavelength follow-up campaign, including near-infrared imaging from HAWKI/VLT, optical from OSIRIS/GTC, X-ray observations from the Chandra X-ray Observatory and at submillimetre/millimetre wavelengths from SMA. Optical/NIR spectroscopy was performed with X-shooter/VLT. We detect the X-ray and NIR afterglow of the burst and determine a redshift of z=2.1974±0.0002 through identification of emission lines of [OII], [OIII] and H-α from the host galaxy of the GRB. This implies an energy release of E_iso,γ=(3.0±0.2)x10⁵⁴erg, amongst the most luminous ever detected. The observations of the afterglow indicate high obscuration with A_V>1.5. The host galaxy is compact, with R_1/2<1.6kpc, but luminous, at L∼1.5L^* and has a star formation rate of 91±6M_☉/yr as derived from Hα. As for other highly obscured GRBs, GRB120624B is hosted by a luminous galaxy, which we also prove to be compact, with very intense star formation. It is one of the most luminous host galaxies associated with a GRB, showing that the host galaxies of long GRBs are not always blue dwarf galaxies, as previously thought.