Volume 557, September 2013
|Number of page(s)||8|
|Section||Stellar structure and evolution|
|Published online||27 August 2013|
Near-infrared and optical observations of the failed outbursts of black hole binary XTE J1550−564⋆
1 International Centre for Radio Astronomy Research, Curtin University, GPO Box U1987, WA 6845 Perth, Australia
2 AIM, UMR-E 9005 CEA/DSM-CNRS-Université Paris Diderot, Irfu/Service d’Astrophysique, Centre de Saclay, 91191 Gif-sur-Yvette Cedex, France
3 Institut Universitaire de France, 103 boulevard Saint-Michel, 75005 Paris, France
Accepted: 17 July 2013
Context. A number of low mass X-ray binaries (LMXBs) undergo “failed outbursts” in which, instead of evolving through the canonical states, they remain in a hard state throughout the outburst. While the sources of X-ray and radio emission in the hard state are relatively well understood, the origin of the near-infrared (NIR) and optical emission is more complex though it likely stems from an amalgam of different emission processes, occurring as it does, at the intersecting wavelengths of those processes.
Aims. We aim to identify the NIR/optical emission region(s) during a number of failed outbursts of one such LMXB and black hole candidate, XTE J1550−564, in order to confirm or refute their classification as hard-state, failed outbursts.
Methods. We present unique NIR/optical images and spectra, obtained with the ESO–New Technology Telescope, during the failed outbursts of 2001 and 2000. We compare the NIR/optical photometric, timing, and spectral properties with those expected for the different emission mechanisms in the various LMXB states.
Results. The NIR/optical data are consistent with having come from reprocessing of X-rays in the accretion disk, with no evidence of direct thermal emission from the disk itself. However, the observed variability in high-cadence NIR light curves suggest that the radio jet extends and contributes to the NIR wavelengths.
Conclusions. We find that these failed outbursts did not transition to an intermediate state but remained in a true, hard state where there was no sign of jet quenching or deviation from the observed hard state correlations.
Key words: X-rays: binaries / infrared: stars / X-rays: individuals: XTEJ1550-564
© ESO, 2013
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