Rapid optical and X-ray timing observations of GX 339–4: flux correlations at the onset of a low/hard state†

  1. P. Gandhi1,*,
  2. K. Makishima1,2,
  3. M. Durant3,
  4. A. C. Fabian4,
  5. V. S. Dhillon5,
  6. T. R. Marsh6,
  7. J. M. Miller7,
  8. T. Shahbaz3,
  9. H. C. Spruit8

Article first published online: 12 AUG 2008

DOI: 10.1111/j.1745-3933.2008.00529.x

Issue

Monthly Notices of the Royal Astronomical Society: Letters

Monthly Notices of the Royal Astronomical Society: Letters

Volume 390, Issue 1, pages L29–L33, October 2008

Additional Information

How to Cite

Gandhi, P., Makishima, K., Durant, M., Fabian, A. C., Dhillon, V. S., Marsh, T. R., Miller, J. M., Shahbaz, T. and Spruit, H. C. (2008), Rapid optical and X-ray timing observations of GX 339–4: flux correlations at the onset of a low/hard state. Monthly Notices of the Royal Astronomical Society: Letters, 390: L29–L33. doi: 10.1111/j.1745-3933.2008.00529.x

Author Information

  1. 1

    RIKEN Cosmic Radiation Lab, 2-1 Hirosawa, Wakoshi, Saitama 351-0198, Japan

  2. 2

    Department of Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan

  3. 3

    Instituto de Astrofísica de Canarias, La Laguna, E38205 Tenerife, Spain

  4. 4

    Institute of Astronomy, Madingley Road, Cambridge CB3 0HA

  5. 5

    Department of Physics and Astronomy, University of Sheffield, Sheffield S3 7RH

  6. 6

    Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL

  7. 7

    Department of Astronomy, University of Michigan, 500 Church Street, Ann Arbor, MI 48109, USA

  8. 8

    Max-Planck-Institut für Astrophysik, Postfach 1317, 85741 Garching bei München, Germany

* E-mail: pg@crab.riken.jp

  • †

    Based on observations carried out in ESO programmes 079.D-0535 and 279.D-5021, and Rossi X-ray Timing Explorer proposal number 93119.

Publication History

  1. Issue published online: 2 OCT 2008
  2. Article first published online: 12 AUG 2008
  3. Accepted 2008 July 8. Received 2008 July 8; in original form 2008 June 21

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Keywords:

  • accretion, accretion discs;
  • black hole physics;
  • stars: individual: GX 339−4;
  • X-rays: binaries

ABSTRACT

We present the discovery of optical/X-ray flux correlations on rapid time-scales in the low/hard state of the Galactic black hole GX 339−4. The source had recently emerged from outburst and was associated with a relatively faint counterpart with mag V≈ 17. The optical [Very Large Telescope (VLT)/ULTRACAM] and X-ray (Rossi X-ray Timing Explorer) data show a clear positive cross-correlation function (CCF) signal, with the optical peak lagging X-rays by ∼150 ms, preceded by a shallow rise and followed by a steep decline along with broad anticorrelation dips. An examination of the light curves shows that the main CCF features are reproduced in superpositions of flares and dips. The CCF peak is narrow and the X-ray autocorrelation function (ACF) is broader than the optical ACF, arguing against reprocessing as the origin for the rapid optical emission. X-ray flaring is associated with spectral hardening, but no corresponding changes are detected around optical peaks and dips. The variability may be explained in the context of synchrotron emission with interaction between a jet and a corona. The complex CCF structure in GX 339−4 has similarities to that of another remarkable X-ray binary XTE J1118+480, in spite of showing a weaker maximum strength. Such simultaneous multiwavelength, rapid timing studies provide key constraints for modelling the inner regions of accreting stellar sources.

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