Work

Very Large Telescope and [ITAL]Hubble Space Telescope[/ITAL] Observations of the Host Galaxy of GRB 990705

Year: 2002

Type: article

Abstract: We present Very Large Telescope spectroscopic observations of the GRB 990705 host galaxy and highlight the benefits provided by the prompt phase features of gamma-ray bursts (GRBs) to derive the redshifts of the latter. In the host spectrum, we indeed detect an emission feature that we attribute to the [O II] λλ3726, 3729 doublet and derive an unambiguous redshift z = 0.8424 ± 0.0002 for this galaxy. This is in full agreement with the value z ~ 0.86 ± 0.17 previously derived using a transient absorption edge discovered in the X-ray spectrum of GRB 990705. This burst is therefore the first GRB for which a reliable redshift was derived from the prompt phase emission itself , as opposed to redshift determinations performed using putative host galaxy emission lines or interstellar absorption lines in the GRB afterglows. Deep and high-resolution images of the host of GRB 990705 with the Space Telescope Imaging Spectrograph camera on board the Hubble Space Telescope reveal that the burst occurred in a nearly face-on Sc spiral galaxy typical of disk-dominated systems at 0.75 ≤ z ≤ 1. Assuming a cosmology with H 0 = 65 km s -1 Mpc -1 , Ω m = 0.3, and Ω λ = 0.7, we derive an absolute B magnitude M B = -21.75 for this galaxy and a star formation rate SFR ≈ 5-8 M ☉ yr -1 . Finally, we discuss the implications of using X-ray transient features to derive GRB redshifts with larger burst samples and especially examine the case of short and dark long GRBs.

Source: The Astrophysical Journal

DOI: 10.1086/346072