The afterglow of the short/intermediate-duration gamma-ray burst GRB 000301C: A jet at ^*,**,***

¹ Astronomical Observatory, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen Ø, Denmark e-mail: brian_j@astro.ku.dk, jens@astro.ku.dk, holger@astro.ku.dk
² Institute of Physics and Astronomy, University of Aarhus, 8000 Århus C., Denmark e-mail: jfynbo@eso.org, sholland@nd.edu, bt@ifa.au.dk
³ European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching, Germany e-mail: pmoller@eso.org
⁴ Danish Space Research Institute, Juliane Maries Vej 30, 2100 Copenhagen Ø, Denmark, e-mail: jgu@dsri.dk
⁵ Department of Physics, University of Notre Dame, Notre Dame IN 46556-5670, USA
⁶ Science Institute, Dunhagi 3, University of Iceland, 107 Reykjavik, Iceland, e-mail: gulli@raunvis.hi.is
⁷ Institut d'Astrophysique et de Géophysique, Université de Liège, avenue de Cointe 5, 4000 Liège, Belgium e-mail: burud@astro.ulg.ac.be
⁸ U.S. Naval Observatory, Flagstaff Station, Flagstaff, AZ 86002-1149, USA, e-mail: aah@nofs.navy.mil
⁹ Department of Physical Sciences, University of Hertfordshire, College Lane, Hatfield, Herts AL10 9AB, UK e-mail: nrt@star.herts.ac.uk
¹⁰ Joint Astronomy Centre, 660 N. A'ohoku Place, Hilo, Hawaii 96720, USA e-mail: c.davis@jach.hawaii.edu
¹¹ University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands e-mail: pmv@astro.uva.nl, evert@astro.uva.nl
¹² University of California, Berkeley, Space Sciences Laboratory, Berkeley, CA 94720-7450 USA e-mail: khurley@ssl.berkeley.edu
¹³ NASA Goddard Space Flight Center, Code 661, Greenbelt, MD 20771 USA e-mail: cline@lheavx.gsfc.nasa.gov
¹⁴ NASA Goddard Space Flight Center, Code 691, Greenbelt, MD 20771 USA e-mail: Jacob.I.Trombka.1@gsfc.nasa.gov, xrtpm@leptpm.gsfc.nasa.gov
¹⁵ The Catholic University of America, Department of Physics, Washington, DC 20064 USA e-mail: rstarr@lepvax.gsfc.nasa.gov
¹⁶ The Johns Hopkins University, Applied Physics Laboratory, Laurel, MD 20723 USA e-mail: john.goldsten@jhuapl.edu
¹⁷ Laboratorio de Astrofísica Espacial y Física Fundamental (LAEFF-INTA), PO Box 50727, 28080, Madrid, Spain, e-mail: ajct@iaa.es
¹⁸ Instituto de Astrofísica de Andalucía (IAA-CSIC), PO Box 03004, 18080 Granada, Spain
¹⁹ Astrophysikalisches Institut, Potsdam, Germany, e-mail: jgreiner@aip.de
²⁰ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany e-mail: calj@mpia-hd.mpg.de, Kuemmel@mpia-hd.mpg.de, mundt@mpia-hd.mpg.de

Corresponding author: B. L. Jensen, brian_j@astro.ku.dk

Received: 6 June 2000
Accepted: 19 February 2001

Abstract

We present Ulysses and NEAR data from the detection of the short or intermediate duration (2 s) gamma-ray burst GRB 000301C (2000 March 1.41 UT). The gamma-ray burst (GRB) was localised by the Inter Planetary Network (IPN) and RXTE to an area of ~50 arcmin². A fading optical counterpart was subsequently discovered with the Nordic Optical Telescope (NOT) about 42 h after the burst. The GRB lies at the border between the long-soft and the short-hard classes of GRBs. If GRB 000301C belongs to the latter class, this would be the first detection of an afterglow to a short-hard burst. We present UBRI photometry from the time of the discovery until 11 days after the burst. We also present JHK photometry obtained with UKIRT on 2000 March 4.5 UT (3.1 days after the burst). Finally, we present spectroscopic observations of the optical afterglow obtained with the ESO VLT Antu telescope 4 and 5 days after the burst. The optical light curve is consistent with being achromatic from 2 to 11 days after the burst and exhibits a break. A broken power-law fit yields a shallow pre-break decay power-law slope of , a break time of days after the burst, and a post-break slope of . These properties of the light curve are best explained by a sideways expanding jet in an ambient medium of constant mean density. In the optical spectrum we find absorption features that are consistent with Feii, Civ, Cii, Siii and Lyα at a redshift of . We find evidence for a curved shape of the spectral energy distribution of the observed afterglow. It is best fitted with a power-law spectral distribution with index reddened by an SMC-like extinction law with mag. Based on the Lyα absorption line we estimate the Hi column density to be (N(Hi). This is the first direct indication of a connection between GRB host galaxies and Damped Lyα Absorbers.