The Luminous Infrared Host Galaxy of Short-Duration GRB 100206A

TL;DR

This paper reports the discovery of a luminous infrared galaxy hosting a short-duration gamma-ray burst, revealing that such bursts can occur in massive, star-forming, and metal-rich galaxies, challenging previous assumptions about their environments.

Contribution

It presents the first detailed analysis of a short GRB host galaxy that is a luminous infrared galaxy with high star formation and metallicity, expanding the known diversity of host environments.

Findings

Host galaxy is a luminous infrared galaxy with high star formation rate (~30 M_sun/yr).

The galaxy has the highest metallicity among known GRB hosts.

The host's properties suggest an older progenitor, not necessarily linked to recent star formation.

Abstract

The known host galaxies of short-hard gamma-ray bursts (GRBs) to date are characterized by low to moderate star-formation rates and a broad range of stellar masses. In this paper, we positionally associate the recent unambiguously short-hard Swift GRB 100206A with a disk galaxy at redshift z=0.4068 that is rapidly forming stars at a rate of ~30 M_sun/yr, almost an order of magnitude higher than any previously identified short GRB host. Using photometry from Gemini, Keck, PAIRITEL, and WISE, we show that the galaxy is very red (g-K = 4.3 AB mag), heavily obscured (A_V ~ 2 mag), and has the highest metallicity of any GRB host to date (12 + log[O/H]_KD02 = 9.2): it is a classical luminous infrared galaxy (LIRG), with L_IR ~ 4 x 10^11 L_sun. While these properties could be interpreted to support an association of this GRB with very recent star formation, modeling of the broadband spectral energy distribution also indicates that a substantial stellar mass of mostly older stars is present. The current specific star-formation rate is modest (specific SFR ~ 0.5 Gyr^-1), the current star-formation rate is not substantially elevated above its long-term average, and the host morphology shows no sign of recent merger activity. Our observations are therefore equally consistent with an older progenitor, similar to what is inferred for other short-hard GRBs. Given the precedent established by previous short GRB hosts and the significant fraction of the Universe's stellar mass in LIRG-like systems at z >~0.3, an older progenitor represents the most likely origin of this event.