Near-infrared and optical observations of the failed outbursts of black hole binary XTE J1550−564
Abstract
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.
Origin : Publication funded by an institution
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