Astron. Astrophys. 359, 941-947 (2000)

ISO detection of a 60 µm source near GRB 970508

L. Hanlon ¹, R.J. Laureijs ², L. Metcalfe ², B. McBreen ¹, B. Altieri ³, A. Castro-Tirado ^4,5, A. Claret ⁶, E. Costa ⁷, M. Delaney ^1,8, M. Feroci ⁷, F. Frontera ⁹, T. Galama ¹⁰, J. Gorosabel ⁴, P. Groot ¹⁰, J. Heise ¹¹, M. Kessler ², C. Kouveliotou ¹², E. Palazzi ⁹, J. van Paradijs  ^10,13, L. Piro ⁷ and N. Smith <sup>14

1</sup> Department of Experimental Physics, University College Dublin, Belfield, Stillorgan Road, Dublin 4, Ireland
² ISO Data Centre, Astrophysics Division, ESA, Villafranca, Spain
³ XMM Data Centre, Astrophysics Division, ESA, Villafranca, Spain
⁴ Laboratorio de Astrofísica Espacial y Física Fundamental, Villafranca del Castillo, P.O. Box 50727, 28080 Madrid, Spain
⁵ Instituto de Astrofísica de Andalucía (IAA-CSIC), P.O. Box 03004, 18080 Granada, Spain
⁶ Service d'Astrophysique, CEA/DSM/DAPNIA Saclay, Orme des Merisiers, 91191 Gif-sur-Yvette Cédex, France
⁷ Istituto Astrofisica Spaziale, CNR, 00133 Roma, Italy
⁸ Stockholm Observatory, 133 36 Saltsjöbaden, Sweden
⁹ ITESRE-CNR, Bologna, Italy
¹⁰ Astronomical Institut `Anton Pannekoek', University of Amsterdam, Amsterdam, The Netherlands
¹¹ SRON Utrecht, The Netherlands
¹² USRA at NASA/MSFC, Huntsville AL, USA
¹³ Physics Department, University of Alabama, Huntsville, USA
¹⁴ Department of Applied Physics and Instrumentation, Cork Institute of Technology, Cork, Ireland

Received 25 April 2000 / Accepted 9 May 2000

Abstract

The Infrared Space Observatory observed the field of the -ray burst GRB 970508 with the CAM and PHT instruments on May 21 and 24, 1997 and with PHT in three filters in November 1997. A source at 60 µm (flux in May of mJy) was detected near the position of the host galaxy of this -ray burst. The source was detected again in November 1997, at a marginally lower flux ( mJy). A Galactic cirrus origin and a stellar origin for the emission can be ruled out on the basis of the infrared colours. The marginal evidence for variability in the 60 µm flux between May and November is not sufficient to warrant interpretation of the source as transient fireball emission. However, the infrared colours are physically reasonable if attributed to conventional dust emission from a single blackbody source. The probability of detecting a 60 µm source by chance in a PHT beam down to a detection limit of 50 mJy is . If the source is at the redshift of the host galaxy of the -ray burst the fluxes and upper limits at wavelengths from 12 µm to 170 µm indicate it is an ultraluminous infrared galaxy ( ). The star formation rate is estimated to be several hundred solar masses per year, depending significantly on model-dependent parameters. If this source is associated with the host galaxy of GRB 970508, progenitor models which associate GRBs with star-forming regions are favoured.

Key words: gamma rays: bursts gamma rays: observations infrared: galaxies infrared: general ISM: dust, extinction

Send offprint requests to: L. Hanlon (lhanlon@bermuda.ucd.ie)

SIMBAD Objects

Contents

• 1. Introduction
• 2. Observations of GRB 970508
• 3. ISO Observations
• 4. ISOPHOT data processing
• 5. Results
  • 5.1. Assessment of uncertainties in the maps
• 6. Discussion
  • 6.1. Origin of the 60 µm emission
  • 6.2. Probability of a chance superposition
  • 6.3. The star formation rate of the 60 µm source
• 7. Conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 2000

Online publication: July 13, 2000
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