INTEGRAL and XMM-Newton observations of GRB 040106

Abstract

On January 6th 2004, the IBAS burst alert system triggered the 8th gamma-ray burst (ORB) to be located by the INTEGRAL satellite. The position was determined and publicly distributed within 12 s, prompting ESA's XMM-Newton to execute a ToO observation just 5 h later, during which an X-ray afterglow was detected. The GRB had a duration ∼52 s with two distinct pulses separated by ∼42 s. Here we present the results of imaging and spectral analyses of the prompt emission from INTEGRAL data and the X-ray afterglow from XMM-Newton data. The γ-ray spectrum is consistent with a single power-law of photon index -1.72 ± 0.15. The fluence (20-200 keV) was 8.2 × 10-7 erg cm-2. The X-ray afterglow (Fv(t) α v -βX t-δ) was extremely hard with βX = 0.47 ± 0.01 and δ = 1.46 ± 0.04. The 2-10 keV flux 11 h after the burst was 1.1 × 10-12 erg cm -2 s-1. The time profile of the GRB is consistent with the observed trends from previous analysis of BATSE GRBs. We find that the X-ray data are not well-fit by either a simple spherical fireball or by a speading jet, expanding into a homogeneous medium or a wind environment. Based on previously determined correlations between GRB spectra and redshift, we estimate a redshift of ∼0.9-0.4+0.5 (1σ) and a lower limit on the isotropic radiated energy of ∼5 × 1051 erg in this burst. © ESO 2005.