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RXTE ASM finds the Rapid Burster (MXB1730-335) at a Nearly Constant Elevated Intensity

ATEL # 1939; Alan M. Levine and Ronald A. Remillard (MIT) for the RXTE team at GSFC and MIT
on 23 Feb 2009; 16:43 UT
Distributed as an Instant Email Notice (Request for Observations)
Password Certification: Alan M. Levine (

Subjects: X-ray, Request for Observations, Binaries, Neutron Stars, Transients

Over the 13 years of monitoring of MXB1730-335 (the Rapid Burster; ASM catalog entry x1730-333) by the RXTE ASM, the source has most often been seen at low intensities, i.e., below 10 mcrab. This low intensity state is punctuated by outbursts which generally have a fast rise to a peak intensity of 100 mcrab (1.5-12 keV) or more and a roughly exponential decay over 2 to 4 weeks. The outbursts have occurred quasiperiodically at intervals of 100 to 200 or so days. Recent coverage during the time interval MJD 54775 (2008 Nov 5) to MJD 54865 (2009 Feb 3) by the ASM of MXB1730-335 was poor because of the proximity of the Sun to the Galactic bulge region. An outburst may have occurred during this interval; this is suggested by the pattern of outbursts over the last year or so in which 20 day long outbursts occur every 100 to 110 days. According to this recent pattern, the source would have been in outburst from about MJD 54835 to MJD 54855. In the 17 days from MJD 54868 (2009 Feb 6) through MJD 54884 (2009 Feb 22) the ASM daily average intensities are all about 50 mcrab. While there are a few other instances where the source remained roughly steady for as long as 14 days, all appear to have been plateaus during outburst decays. The present behavior is unusual. We encourage observations of MXB1730-335 with other instruments.

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R. E. Rutledge , Editor
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