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ATEL # 1024; Alan M. Levine (MIT), Ron A. Remillard (MIT), and the ASM team at MIT and NASA/GSFC
on 8 Mar 2007; 19:42 UT
Distributed as an Instant Email Notice (Transients)
Password Certification: Alan M. Levine (email@example.com)
Subjects: X-ray, Binaries, Black Holes, Transients
Observations with the RXTE All-Sky Monitor reveal an outburst that is consistent with being a new outburst of the previously detected transient source XTE J1856+053 (Marshall et al. 1996, IAU Circ. No. 6504; Barret et al. 1996, IAU Circ. No. 6519). The outburst appears to begin on 2007 February 28 (1.5-12 keV intensity 23 +/- 6 mCrab) or March 1 (42 +/- 9 mCrab). The intensity rose steadily until 2007 March 5 when it was 69 +/- 4 mCrab. Through March 8, the intensity has remained in the range 66-74 mCrab. The ASM hardness ratios are HR1 (3-5 keV/1.5-3 keV) = 0.89 +/- 0.04 and HR2 (5-12 keV/3-5 keV) = 0.37 +/- 0.06. These values indicate a soft spectrum and thereby suggest the source is a binary system containing a stellar-mass black hole.