Strategies for prompt searches for GRB afterglows: The discovery of the GRB 001011 optical/near-infrared counterpart using colour-colour selection ^*

¹ Danish Space Research Institute, Juliane Maries Vej 30, 2100 Copenhagen Ø, Denmark e-mail: jgu@dsri.dk
² European Southern Observatory, Karl–Schwarzschild–Straße 2, 85748 Garching, Germany e-mail: jfynbo@eso.org e-mail: pmoller@eso.org
³ Astronomical Observatory, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen Ø, Denmark e-mail: jens@astro.ku.dk e-mail: holger@astro.ku.dk e-mail: lise@astro.ku.dk e-mail: brianj@astro.ku.dk
⁴ Observatoire Midi-Pyrénées (LAS), 14 avenue E. Belin, 31400 Toulouse, France
⁵ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany e-mail: cwolf@mpia-hd.mpg.de
⁶ Division of Astronomy, PO Box 3000, 90014 University of Oulu, Finland e-mail: michael.andersen@oulu.fi
⁷ Blackett Laboratory, Imperial College, Prince Consort Road, London SW7 2BW, UK e-mail: j.afonso@ic.ac.uk
⁸ Laboratoire d'Astronomie Spatiale, Traverse du Siphon, BP 8, 13376 Marseille, France e-mail: Marie.Treyer@astrsp-mrs.fr
⁹ Department of Astronomy, University of Toronto, 60 St. George Street, Toronto, ON, M5S 3H8, Canada e-mail: mallen@astro.utoronto.ca
¹⁰ Laboratorio de Astrofísica Espacial y Física Fundamental (LAEFF-INTA), PO Box 50727, 28080 Madrid, Spain e-mail: ajct@laeff.esa.es
¹¹ Instituto de Astrofísica de Andalucía (IAA-CSIC), PO Box 03004, 18080 Granada, Spain e-mail: ajct@iaa.es
¹² Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA e-mail: fruchter@stsci.edu
¹³ Astrophysikalisches Institut, Potsdam, Germany e-mail: jgreiner@aip.de
¹⁴ Osservatorio Astronomico di Trieste, via Tiepolo 11, 34131 Trieste, Italy e-mail: pian@tesre.bo.cnr.it
¹⁵ University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands e-mail: pmv@astro.uva.nl; lexk@astro.uva.nl; evert@astro.uva.nl; isabel@astro.uva.nl; edvdh@astro.uva.nl
¹⁶ Istituto Tecnologie e Studio Radiazioni Extraterrestri, CNR, via Gobetti 101, 40129 Bologna, Italy e-mail: filippo@tesre.bo.cnr.it; masetti@tesre.bo.cnr.it; eliana@tesre.bo.cnr.it
¹⁷ Thüringer Landessternwarte Tautenburg, 07778 Tautenburg, Germany e-mail: klose@tls-tautenburg.de
¹⁸ NASA MSFC, SD-50, Huntsville, AL 35812, USA e-mail: kouveliotou@eagles.msfc.nasa.gov
¹⁹ Department of Physical Sciences, University of Hertfordshire, College Lane, Hatfield, Herts AL10 9AB, UK e-mail: nrt@star.herts.ac.uk
²⁰ Department of Physics and Astronomy, State University of New York, Stony Brook, NY 11794-3800, USA e-mail: rwijers@astro.sunysb.edu

Corresponding author: J. Gorosabel, jgu@dsri.dk

Received: 19 September 2001
Accepted: 8 November 2001

Abstract

We report the discovery of the optical and near-infrared counterparts to GRB 001011. The GRB 001011 error box determined by Beppo-SAX was simultaneously imaged in the near-infrared by the 3.58-m New Technology Telescope and in the optical by the 1.54-m Danish Telescope ~8 hr after the gamma-ray event. Here we implement the colour-colour discrimination technique proposed by Rhoads ([CITE]) and extend it using near-IR data as well. We present the results provided by an automatic colour-colour discrimination pipe-line developed to discern the different populations of objects present in the GRB 001011 error box. Our software revealed three candidates based on single-epoch images. Second-epoch observations carried out ~3.2 days after the burst revealed that the most likely candidate had faded, thus identifying it with the counterpart to the GRB. In deep R-band images obtained 7 months after the burst a faint () elongated object, presumably the host galaxy of GRB 001011, was detected at the position of the afterglow. The GRB 001011 afterglow is the first discovered with the assistance of colour-colour diagram techniques. We discuss the advantages of using this method and its application to error boxes determined by future missions.