Anatomy of a dark burst – the afterglow of GRB 060108

  1. S. R. Oates1,*,
  2. C. G. Mundell2,
  3. S. Piranomonte3,
  4. K. L. Page4,
  5. M. De Pasquale1,
  6. A. Monfardini2,5,
  7. A. Melandri2,
  8. S. Zane1,
  9. C. Guidorzi2,
  10. D. Malesani6,
  11. A. Gomboc2,7,
  12. N. Bannister4,
  13. A. J. Blustin1,
  14. M. Capalbi8,
  15. D. Carter2,
  16. P. D'Avanzo9,10,
  17. S. Kobayashi2,
  18. H. A. Krimm11,12,
  19. P. T. O'Brien4,
  20. M. J. Page1,
  21. R. J. Smith2,
  22. I. A. Steele2,
  23. N. Tanvir13

Article first published online: 31 AUG 2006

DOI: 10.1111/j.1365-2966.2006.10866.x

Issue

Monthly Notices of the Royal Astronomical Society

Monthly Notices of the Royal Astronomical Society

Volume 372, Issue 1, pages 327–337, October 2006

Additional Information

How to Cite

Oates, S. R., Mundell, C. G., Piranomonte, S., Page, K. L., Pasquale, M. D., Monfardini, A., Melandri, A., Zane, S., Guidorzi, C., Malesani, D., Gomboc, A., Bannister, N., Blustin, A. J., Capalbi, M., Carter, D., D'Avanzo, P., Kobayashi, S., Krimm, H. A., O'Brien, P. T., Page, M. J., Smith, R. J., Steele, I. A. and Tanvir, N. (2006), Anatomy of a dark burst – the afterglow of GRB 060108. Monthly Notices of the Royal Astronomical Society, 372: 327–337. doi: 10.1111/j.1365-2966.2006.10866.x

Author Information

  1. 1

    Mullard Space Science Laboratory, University College of London, Holmbury St Mary, Dorking, Surrey RH5 6NT

  2. 2

    Astrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Egerton Wharf, Birkenhead CH41 1LD

  3. 3

    INAF, Osservatorio Astronomico di Roma, via di Frascati 33, I-00040 Monteporzio Catone (Roma), Italy

  4. 4

    Department of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH

  5. 5

    ITC-IRST and INFN, Trento, via Sommarive 18, I-38050 Povo, Italy

  6. 6

    International School for Advanced Studies (SISSA-ISAS), via Beirut 2-4, I-34014 Trieste, Italy

  7. 7

    Department of Physics, University of Ljubljana, Jadranska 19, 6100 Ljubljana, Slovenia

  8. 8

    ASI Science Data Center, via G. Galilei 5, I-00044 Frascati (Roma), Italy

  9. 9

    Dipartimento di Fisica e Matematica, University of Insubria, via Valleggio 11, I-22100 Como, Italy

  10. 10

    INAF, Osservatorio Astronomico di Brera, via E. Bianchi 46, I-23807 Merate (Lc), Italy

  11. 11

    NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA

  12. 12

    Universities Space Research Association, 10211 Wincopin Circle, Suite 500,Columbia, MD 21044-3432, USA

  13. 13

    Centre for Astrophysics Research, University of Hertfordshire, College Lane, Hatfield AL109AB

* E-mail: sro@mssl.ucl.ac.uk

Publication History

  1. Issue published online: 5 SEP 2006
  2. Article first published online: 31 AUG 2006
  3. Accepted 2006 July 24. Received 2006 July 21; in original form 2006 July 6

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Keywords:

  • gamma-rays: bursts

ABSTRACT

We present a multiwavelength study of GRB 060108 – the 100th gamma-ray burst discovered by Swift. The X-ray flux and light curve (three segments plus a flare) detected with the X-ray Telescope are typical of Swift long bursts.

We report the discovery of a faint optical afterglow detected in deep BVRi′-band imaging obtained with the Faulkes Telescope North beginning 2.75 min after the burst. The afterglow is below the detection limit of the Ultraviolet/Optical Telescope within 100 s of the burst, while is evident in K-band images taken with the United Kingdom Infrared Telescope 45 min after the burst. The optical light curve is sparsely sampled. Observations taken in the R and i′ bands can be fitted either with a single power-law decay in flux, F(t) ∝t−α where α= 0.43 ± 0.08, or with a two-segment light curve with an initial steep decay α1 < 0.88 ± 0.2, flattening to a slope α2∼ 0.31 ± 0.12. A marginal evidence for rebrightening is seen in the i′ band.

Deep R-band imaging obtained ∼12 d post-burst with the Very Large Telescope reveals a faint, extended object (R∼ 23.5 mag) at the location of the afterglow. Although the brightness is compatible with the extrapolation of the slow decay with index α2, significant flux is likely due to a host galaxy. This implies that the optical light curve had a break before 12 d, akin to what observed in the X-rays.

We derive the maximum photometric redshift z < 3.2 for GRB 060108. We find that the spectral energy distribution at 1000 s after the burst, from the optical to the X-ray range, is best fitted by a simple power law, Fν∝ν−β, with βOX= 0.54 and a small amount of extinction. The optical to X-ray spectral index (βOX) confirms GRB 060108 to be one of the optically darkest bursts detected. Our observations rule out a high redshift as the reason for the optical faintness of GRB 060108. We conclude that a more likely explanation is a combination of an intrinsic optical faintness of the burst, a hard optical to X-ray spectrum and a moderate amount of extinction in the host galaxy.

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