Photometry and spectroscopy of GRB 060526: a detailed study of the afterglow and host galaxy of a z = 3.2 gamma-ray burst^⋆,⋆⋆

¹ Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen, Denmark
e-mail: christina.thoene@brera.inaf.it
² INAF – Osservatorio Astronomico di Brera, via Bianchi 46, 23807 Merate ( Lc), Italy
³ Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
⁴ Science Institute, University of Iceland, Dunhaga 3, 107 Reykjavík, Iceland
⁵ Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA 94305, USA
⁶ Institute of Theoretical Astrophysics, University of Oslo, PO Box 1029 Blindern, 0315 Oslo, Norway
⁷ Department of Physics, University of Michigan, Ann Arbor, MI 48109, USA
⁸ Physical Research Laboratory, Ahmedabad – 380 009, India
⁹ Dipartimento di Astronomia, Universita di Bologna, via Ranzani 1, 40127 Bologna, Italy
¹⁰ Kazan Federal University and Academy of Sciences of Tatarstan, Kazan, Russia
¹¹ Department of Astronomy, 601 Campbell Hall, University of California, Berkeley, CA 94720–3411, USA
¹² Space Research Institute (IKI), 84/32 Profsoyuznaya Str, Moscow 117997, Russia
¹³ Department of Astronomy, Yale University, PO Box 208101, New Haven, CT 06520, USA
¹⁴ Astronomical Institute “Anton Pannekoek”, University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
¹⁵ Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey RH5 6NT, UK
¹⁶ UCD School of Physics, University College Dublin, Belfield, Dublin 4, Ireland
¹⁷ Max-Planck-Institute for Extraterrestrial Physics, Giessenbachstraße, 85748 Garching, Germany
¹⁸ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD21218, USA
¹⁹ Ulugh Beg Astronomical Institute, 33 Astronomical Str., Tashkent 700052, Uzbekistan
²⁰ INAF – Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monteporzio Catone, Italy
²¹ Centre for Astrophysics and Cosmology, Science Institute, University of Iceland, Dunhagi 5, 107 Reykjavík, Iceland
²² Instituto de Astrofísica de Andalucía (IAA-CSIC), PO Box 3.004, 18. 080 Granada, Spain
²³ Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen, Denmark
²⁴ Centre for Star and Planet Formation, Geological Museum, Øster Voldgade 5-7, 1350 Copenhagen, Denmark
²⁵ Tübitak National Observatory, Antalya, Turkey
²⁶ Department of Astronomy and Astrophysics, Pennsylvania State University, 525 Davey Lab, University Park, PA 16802, USA
²⁷ Department of Physics, Univ. of Warwick, Coventry, CV4 7AL, UK
²⁸ INAF – Istituto di Astrofisica Spaziale e Fisica Cosmica di Bologna, via Gobetti 101, 40129 Bologna, Italy
²⁹ University of Helsinki Observatory, PO Box 14 ( Tähtitorninmäki), 00014, Finland
³⁰ VU Institute of Theoretical Physics and Astronomy, A. Gostauto 12, 01108 Vilnius, Lithuania
³¹ Space Science Department, Southwest Research Institute, San Antonio, TX 78238, USA
³² Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721, USA
³³ Crimean Astrophysical Observatory, Nauchny, Crimea, 98409, Ukraine
³⁴ Physics Department, University of California at Santa Barbara, 2233B Broida Hall, Santa Barbara, CA 93106, USA
³⁵ Tabasgo Fellow, USA
³⁶ Max-Plank-Institut für Astrophysik, Karl-Schwarzschild Straße 1, 85741 Garching, Germany
³⁷ Department of Physics and Astronomy, University of Leicester, University Road, Leicester, LE1 7RH, UK
³⁸ Second University of Roma “Tor Vergata”, Italy
³⁹ Department of Astronomy, University of Texas at Austin, Austin TX, 78712, USA
⁴⁰ Department of Physics, College of St. Benedict/St. Johns University, Collegeville, MN 56321, USA

Received: 6 June 2008
Accepted: 17 July 2010

Abstract

Aims. With this paper we want to investigate the highly variable afterglow light curve and environment of gamma-ray burst (GRB) 060526 at z = 3.221.

Methods. We present one of the largest photometric datasets ever obtained for a GRB afterglow, consisting of multi-color photometric data from the ultraviolet to the near infrared. The data set contains 412 data points in total to which we add additional data from the literature. Furthermore, we present low-resolution high signal-to-noise spectra of the afterglow. The afterglow light curve is modeled with both an analytical model using broken power law fits and with a broad-band numerical model which includes energy injections. The absorption lines detected in the spectra are used to derive column densities using a multi-ion single-component curve-of-growth analysis from which we derive the metallicity of the host of GRB 060526.

Results. The temporal behaviour of the afterglow follows a double broken power law with breaks at t = 0.090 ± 0.005 and t = 2.401 ± 0.061 days. It shows deviations from the smooth set of power laws that can be modeled by additional energy injections from the central engine, although some significant microvariability remains. The broadband spectral-energy distribution of the afterglow shows no significant extinction along the line of sight. The metallicity derived from S ii and Fe ii of [S/H] = –0.57 ± 0.25 and [Fe/H] = –1.09 ± 0.24 is relatively high for a galaxy at that redshift but comparable to the metallicity of other GRB hosts at similar redshifts. At the position of the afterglow, no host is detected to F775W(AB) = 28.5 mag with the HST, implying an absolute magnitude of the host M(1500 Å)  > –18.3 mag which is fainter than most long-duration hosts, although the GRB may be associated with a faint galaxy at a distance of 11 kpc.