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ATEL # 1122; David M. Smith and Andrey Martchovsky (Physics Dept. and SCIPP, University of California, Santa Cruz), Patricia Boyd and Jean H. Swank (NASA's Goddard Spaceflight Center)
on 29 Jun 2007; 20:28 UT
Distributed as an Instant Email Notice (Request for Observations)
Password Certification: David M. Smith (firstname.lastname@example.org)
Subjects: X-ray, Request for Observations, Binaries, Black Holes
Monitoring observations of LMC X-3 by the Rossi X-ray Timing Explorer (RXTE) show that this black-hole candidate has entered the hard state for the first time since frequent monitoring began in March 2005. Luminosity was declining, and the contribution of the power-law component increasing, over the past several weeks. By June 15, 2007, the disk blackbody and powerlaw components had comparable contributions to the 2-10 keV flux, which was approximately 1.3x10^(-10) erg/cm2/s. On June 22, the source could be fit with a power law of index -2.2 (+/- 0.1), with no thermal component required, and a flux of 2.9x10^(-11) erg/cm2/s. On June 27, the best-fit power-law index was still -2.2 (+/- 0.2), but the flux had dropped to 1.0x10^(-11) erg/cm2/s, more than an order of magnitude below the flux of 12 days earlier.
Deep observations with RXTE have been scheduled. Radio observations to look for changes associated with the possible appearance and/or disappearance of a jet are encouraged, as are x-ray observations with other observatories. Judging from past behavior (Boyd et al. 2002, ApJL 542, L127; Wilms et al. 2001, MNRAS 320, 327) the source will probably return to its usual soft state within a month or less.