The obscured hyper-energetic GRB 120624B hosted by a luminous compact galaxy at z = 2.20

TL;DR

This study analyzes the extremely luminous GRB 120624B at z=2.20, revealing its energetic emission and a luminous, compact host galaxy with intense star formation, challenging previous notions about GRB host galaxies.

Contribution

It provides detailed multi-wavelength observations of one of the most energetic GRBs and characterizes its luminous, compact host galaxy, expanding understanding of GRB environments.

Findings

GRB 120624B has an energy release of (3.0 +/- 0.2) x 10^54 erg.

The host galaxy is luminous, compact, with high star formation rate (~91 M_sun/yr).

The host is not a typical blue dwarf galaxy, but a luminous, compact galaxy.

Abstract

Gamma-ray bursts 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 GRB 120624B, 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 sub-millimetre/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 the identification of emission lines of [OII], [OIII] and H-alpha from the host galaxy of the GRB. This implies an energy release of Eiso = (3.0+/-0.2)x10^54 erg, amongst the most luminous ever detected. The observations of the afterglow indicate high obscuration with AV > 1.5. The host galaxy is compact, with R1/2 < 1.6 kpc, but luminous, at L ~ 1.5 L* and has a star formation rate of 91 +/- 6 Msol/yr as derived from H-alpha. As other highly obscured GRBs, GRB 120624B is hosted by a luminous galaxy, which we also proof to be compact, with a 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.