Astrophys. J., 791, 70 (2014/August-2)
A delayed transition to the hard state for 4U 1630-47 at the end of its 2010 outburst.
TOMSICK J.A., YAMAOKA K., CORBEL S., KALEMCI E., MIGLIARI S. and KAARET P.
Abstract (from CDS):
Here we report on Swift and Suzaku observations near the end of an outburst from the black hole transient 4U 1630-47 and Chandra observations when the source was in quiescence. 4U 1630-47 made a transition from a soft state to the hard state ∼50 days after the main outburst ended. During this unusual delay, the flux continued to drop, and one Swift measurement found the source with a soft spectrum at a 2-10 keV luminosity of L = 1.07x1035 erg/s for an estimated distance of 10 kpc. While such transients usually make a transition to the hard state at L/LEdd= 0.3%-3%, where LEdd is the Eddington luminosity, the 4U 1630-47 spectrum remained soft at L/LEdd= 0.008 M10–1% (as measured in the 2-10 keV band), where M10is the mass of the black hole in units of 10 M☉. An estimate of the luminosity in the broader 0.5-200 keV bandpass gives L/LEdd= 0.03 M10–1%, which is still an order of magnitude lower than typical. We also measured an exponential decay of the X-ray flux in the hard state with an e-folding time of 3.39±0.06 days, which is much less than previous measurements of 12-15 days during decays by 4U 1630-47 in the soft state. With the ∼100 ks Suzaku observation, we do not see evidence for a reflection component, and the 90% confidence limits on the equivalent width of a narrow iron Kα emission line are <40 eV for a narrow line and <100 eV for a line of any width, which is consistent with a change of geometry (either a truncated accretion disk or a change in the location of the hard X-ray source) in the hard state. Finally, we report a 0.5-8 keV luminosity upper limit of <2x1032 erg/s in quiescence, which is the lowest value measured for 4U 1630-47 to date.
accretion, accretion disks - black hole physics - stars: individual: (4U 1630-47) - X-rays: general - X-rays: stars
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