X‐Ray Jet Emission from the Black Hole X‐Ray Binary XTE J1550−564 withChandrain 2000

Abstract

We have discovered an X-ray jet due to material ejected from the black hole X-ray transient XTE J1550-564. The discovery was first reported in 2002 by Corbel and coworkers, and here we present an analysis of the three Chandra observations made between 2000 June and September. For these observations, a source is present that moves in an eastward direction away from the point source associated with the compact object. The separation between the new source and the compact object changes from 213 in June to 234 in September, implying a proper motion of 21.2 ± 7.2 mas day-1, a projected separation of 0.31-0.85 pc, and an apparent jet velocity between 0.34 ± 0.12 and 0.93 ± 0.32 times the speed of light for a source distance range of d = 2.8-7.6 kpc. These observations represent the first time that an X-ray jet proper-motion measurement has been obtained for any accretion-powered Galactic or extragalactic source. While this work deals with the jet to the east of the compact object, the western jet has also been detected in the X-ray and radio bands. The most likely scenario is that the eastern jet is the approaching jet and that the jet material was ejected from the black hole in 1998. Along with a 1998 VLBI proper-motion measurement, the Chandra proper motion indicates that the eastern jet decelerated between 1998 and 2000. There is evidence that the eastern jet is extended by ±2''-3'' in the direction of the proper motion. The upper limit on the source extension in the perpendicular direction is ±15, which corresponds to a jet opening angle of less than 75. The X-ray jet energy spectrum is well but not uniquely described by a power law with an energy index of α = -0.8 ± 0.4 (Sν ∝ να) and interstellar absorption. The eastern jet was also detected in the radio band during an observation made within 7.4 days of the June Chandra observation. The overall radio flux level is consistent with an extrapolation of the X-ray power law with α = -0.6. The 0.3-8 keV X-ray jet luminosity is in the range (3-24) × 1032 ergs s-1 for the June observation using the distance range above but is a factor of ~2-3 lower for the later observations. We cannot definitively determine the X-ray emission mechanism, but a synchrotron origin is viable and may provide the simplest explanation for the observations.