Volume 529, May 2011
|Number of page(s)||8|
|Section||Stellar structure and evolution|
|Published online||18 March 2011|
Near-infrared jet emission in the microquasar XTE J1550-564 ⋆
Laboratoire AIM (UMR 7158 CEA/DSM-CNRS-Université Paris Diderot), Irfu/Service d’Astrophysique, CEA-Saclay, 91191 Gif-sur-Yvette Cedex, France
2 UJF-Grenoble 1/CNRS-INSU, Institut de Planétologie et d’Astrophysique de Grenoble (IPAG) UMR 5274, 38041 Grenoble, France
3 GEPI, Observatoire de Paris-Meudon, 5 place Jules Janssen, 92195 Meudon, France
Received: 15 August 2010
Accepted: 15 February 2011
Context. Microquasars are accreting Galactic sources that are also observed to launch relativistic jets. A key signature of the ejection is non-thermal radio emission. The level of this jet component at high frequencies is still poorly constrained.
Aims. The X-ray binary and microquasar black hole candidate XTEJ1550-564 exhibited a faint X-ray outburst in April 2003 during which it stayed in the X-ray low/hard state. We took optical and near-infrared (NIR) observations with the ESO/NTT telescope during this outburst to distinguish the various contributions to the spectral energy distribution (SED) and investigate the presence of a jet component.
Methods. Photometric and spectroscopic observations allowed us to construct an SED and also to produce a high time-resolution lightcurve.
Results. The SED shows an abrupt change of slope from the NIR domain to the optical. The NIR emission is attributed to non-thermal synchrotron emission from the compact, self-absorbed jet that is known to be present in the low/hard state. This is corroborated by the fast variability, colours, lack of prominent spectral features and evidence for intrinsic polarisation. The SED suggests the jet break from the optically thick to the thin regime occurs in the NIR.
Conclusions. The simultaneous optical-NIR data allow an independent confirmation of jet emission in the NIR. The transition to optically thin synchrotron occurs at NIR frequencies or below, which leads to an estimated characteristic size ≳ 2 × 108 cm and magnetic field ≲ 5 T for the jet base, assuming a homogeneous one-zone synchrotron model.
Key words: accretion, accretion disks / X-rays: individuals: XTE J1550-564 / binaries: close / ISM: jets and outflows / infrared: stars / X-rays: binaries
© ESO, 2011
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