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Astrophysical Journal Letters 740 (2011) L13
A variable mid-infrared synchrotron break associated with the compact jet in GX 339-4
P. Gandhi, A.W. Blain, D. M. Russell, P. Casella, J. Malzac1, S. Corbel2, 3, P. D'Avanzo, F. W. Lewis, S. Markoff, M. Cadolle Bel, P. Goldoni2, 4, S. Wachter, D. Khangulyan, A. Mainzer

Many X-ray binaries remain undetected in the mid-infrared, a regime where emission from their compact jets is likely to dominate. Here, we report the detection of the black hole binary GX 339-4 with the Wide-field Infrared Survey Explorer (WISE) during a very bright, hard accretion state in 2010. Combined with a rich contemporaneous multiwavelength dataset, clear spectral curvature is found in the infrared, associated with the peak flux density expected from the compact jet. An optically-thin slope of ~-0.7 and a jet radiative power of >6x10^{35} erg/s (d/8 kpc)^2 are measured. A ~24 h WISE light curve shows dramatic variations in mid-infrared spectral slope on timescales at least as short as the satellite orbital period ~95 mins. There is also significant change during one pair of observations spaced by only 11 s. These variations imply that the spectral break associated with the transition from self-absorbed to optically-thin jet synchrotron radiation must be varying across the full wavelength range of ~3-22 microns that WISE is sensitive to, and more. Based on four-band simultaneous mid-infrared detections, the break lies at ~5x10^{13} Hz in at least two epochs of observation, consistent with a magnetic field B~1.5x10^4 G assuming a single-zone synchrotron emission region. The observed variability implies that either B, or the size of the acceleration zone above the jet base, are being modulated by factors of ~10 on relatively-short timescales.
1 :  IRAP - Institut de recherche en astrophysique et planétologie
2 :  SAp - Service d'Astrophysique
3 :  AIM - UMR 7158 - Astrophysique Interactions Multi-échelles
4 :  APC - UMR 7164 - AstroParticule et Cosmologie
Physique/Astrophysique/Phénomènes cosmiques de haute energie

Planète et Univers/Astrophysique/Phénomènes cosmiques de haute energie
accretion – accretion disks – black hole physics – stars – individual (GX339-4) – X-rays – binaries
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