Highly extinguished host galaxy of the dark GRB 020819

Abstract

We analyse the properties of the host galaxy of the optically dark gamma-ray burst (GRB) 020819 (z = 0.41) and discuss the possible implications in the context of "dark" GRBs. We present g'r'i'z'JHK photometry of the host galaxy and fit the broad spectral energy distribution including the public Spitzer IRAC data using stellar population models. The broad spectral energy distribution (SED) indicates a high extinction, A_V ~ 1.8 - 2.6 mag, for this relatively massive galaxy. This is the highest global extinction for a GRB host galaxy with a robust spectroscopic redshift. The properties of the host galaxy are indicative of dusty, intense star-formation, which differ from those of the current sample of GRB hosts. This implies that the dust extinction is one of the main reasons for the darkness of low-redshift bursts and that the long GRB host population is far more diverse than previously anticipated.