Multiwavelength study of the very long GRB 020410

Abstract

GRB 020410 is by far the longest gamma-ray burst (with a duration of about 1600 s) to have been followed up from the X-ray through the radio regime. Afterglow emission was detected in X-rays and at optical wavelengths whereas no emission was detected at 8 GHz brighter than 120 muJy. The decaying X-ray afterglow, back-extrapolated to 11 h after the burst, had a flux of 7.9 x 10(-12) erg cm(-2) s(-1) (2-10 keV); the brightest detected so far. No direct redshift determination is available yet for this GRB, but according to the empirical relationship between the peak energy in the nuF(nu) spectrum and the isotropic energy output, z is constrained in the range 0.9-1.5. The reconstructed optical afterglow light curve implies at least two breaks in the simple power law decay. This may be related to emergence of an SN, or refreshment of the external shock by a variation in the circumstellar medium. Considering the backward extrapolation of the 2-10 keV afterglow decay, the prompt lightcurve variability and its spectral evolution, we conclude that the long duration of this event is due to a prolonged activity of the "central engine".