GRB 060605: multi-wavelength analysis of the first GRB observed using integral field spectroscopy^*

¹ Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany e-mail: ferrero@tls-tautenburg.de
² Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstrasse, 85748 Garching, Germany
³ INAF - Istituto di Astrofisica Spaziale e Fisica Cosmica di Bologna, via Gobetti 101, 40129 Bologna, Italy
⁴ Dipartimento di Fisica, Università di Ferrara, via Saragat 1, 44100 Ferrara, Italy
⁵ Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
⁶ Department of Astrophysics and Astronomy, Pennsylvania State University, 525 Davey Lab. University Park, PA 16802, USA
⁷ Mullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking, Surrey RH5 6NT, UK
⁸ Centro Astronómico Hispano Alemán de Calar Alto, Calle Jesus Durban Remon 2-2, 04004 Almería, Spain
⁹ Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen, Denmark
¹⁰ Astroparticle Physics Laboratory, Mail Code 661, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
¹¹ Instituto de Astrofísica de Andalucía (IAA-CSIC), Apartado de Correos 3.004, 18080 Granada, Spain

Received: 15 April 2008
Accepted: 12 February 2009

Abstract

The long and relatively faint gamma-ray burst GRB 060605 detected by Swift/BAT lasted about 20 s. Its afterglow could be observed with Swift/XRT for nearly 1 day, while Swift/UVOT could detect the afterglow during the first 6 h after the event. Here, we report on integral field spectroscopy of its afterglow performed with PMAS/PPak mounted at the Calar Alto 3.5 m telescope. In addition, we report on a detailed analysis of XRT and UVOT data and on the results of deep late-time VLT observations that reveal the GRB host galaxy. We find that the burst occurred at a redshift of , possibly associated with a faint, R_C = 26.4 ± 0.3 host. Based on the optical and X-ray data, we deduce information on the SED of the afterglow, the position of the cooling frequency in the SED, the nature of the circumburst environment, its collimation factor, and its energetics. We find that the GRB fireball was expanding into a constant-density medium and that the explosion was collimated with a narrow half-opening angle of about 2.4 degrees. The initial Lorentz factor of the fireball was about 250; however, its beaming-corrected energy release in the gamma-ray band was comparably low. The optical, X-ray afterglow, on the other hand, was rather luminous. Finally, we find that the data are consistent within the error bars with an achromatic evolution of the afterglow during the suspected jet break time at about 0.27 days after the burst.