RXTE, MAXI and Swift Observations of a New Anomalous Low State in LMC X-3
Abstract
We report the discovery of a new Anomalous Low State (ALS) of the black-hole X-ray binary LMC X-3. LMC X-3 typically varies smoothly and continuously between the high/soft state (with an ultra-soft spectrum plus a hard X-ray tail) and the low/hard state (with a simpler power law spectrum, and high-frequency (0.1-100 Hz) broadband variability) on timescales hundreds of times the 1.7-day orbital period. Recently we discovered two extended low/hard states in LMC X-3 from RXTE data (Smale & Boyd 2012), similar to those observed in the canonical precessing accretion disk source Her X-1. During ALSs, the source is ~15 times fainter than normal low/hard states (corresponding to about 1.3x10-4LEdd), and remains low 5-10 times longer than a typical low/hard state. On ~2011Dec02, RXTE observed LMC X-3 to enter a new ALS. The source stayed flat/off through the end of the RXTE mission. We combine data from the MAXI X-ray All-sky monitor with the RXTE data, yielding continuous coverage of the new ALS. Swift also regularly observed LMC X-3 from 2011Nov, including excellent coverage during the new ALS. The system again drops to historically low levels, stays consistently below ~5x1035 erg/s, often undetectable, for ~90 days before quickly brightening. This is accompanied by a large decrease in the UV flux, followed by a rapid brightening. The UV dimming is a function of wavelength: the UVW2 flux 1894Å) drops to 35% of its typical value, while the U flux 3275Å) drops to 60%. The UV brightening leads the X-ray increase by at least 8 days, consistent with previous optical long-term monitoring (Brocksopp et al., 2001). We suggest that the system is in a true “off” state during ALSs, akin to quiescence, implying that LMC X-3 is perhaps not truly a persistent X-ray source, but a transient whose recurrence time is short.
- Publication:
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American Astronomical Society Meeting Abstracts #221
- Pub Date:
- January 2013
- Bibcode:
- 2013AAS...22114234B