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ATEL # 2365; John A. Tomsick (SSL/UC Berkeley), Nikolai Shaposhnikov (CRESST and NASA/GSFC), and Jean H. Swank (NASA/GSFC)
on 4 Jan 2010; 1:41 UT
Distributed as an Instant Email Notice (Transients)
Password Certification: John A. Tomsick (firstname.lastname@example.org)
Subjects: X-ray, Black Holes, Transients
Referred to by ATEL #: 2370
Observations of 4U 1630-47 were made with the Rossi X-ray Timing Explorer (RXTE), following a report that this black hole transient is now in outburst (Tomida et al., ATEL#2363). The RXTE 3-25 keV spectrum from 2010 Jan. 1 is well-described by a model consisting of a disk-blackbody plus power-law model with absorption. The disk-blackbody temperature is Tin = 1.19 +/- 0.01 keV, and this component dominates below 7 keV. A hard power-law component with a photon index of 1.68 +/- 0.07 dominates above 15 keV. On Jan. 1, 0.5 h UT, the 2-10 keV absorbed flux was 2.78e-9 ergs/cm2/s (139 mCrab), on Jan. 1, 19.3 h UT, the flux was 3.34e-9 ergs/cm2/s (167 mCrab), and on Jan. 3, 1.1 h UT, it was 3.81e-9 ergs/cm2/s (191 mCrab), indicating that the source is continuing to brighten. The strong disk-blackbody component along with a low level of timing noise (<2.2% rms in the 0.01-10 Hz frequency range) suggest that the source is in a soft state (likely the thermal-dominant state). Although the hard power-law could indicate a different (and very unusual) state, we suspect that the hard X-ray emission is contaminated by emission from nearby sources. During previous outbursts, Tomsick et al. (2005, ApJ, 630, 413) have found evidence that IGR J16358-4726 and/or IGR J16320-4751 can contaminate RXTE spectra of 4U 1630-47.