Outburst of MXB 1730-335

ATel #32; D. Fox, D. Smith, W. Lewin (MIT), and R. Rutledge (Caltech), on behalf of a large collaboration
on 20 Aug 1998; 04:55 UT
Distributed as an Instant Email Notice Transients
Credential Certification:

Tweet

The Rapid Burster (MXB 1730-335) has been detected by the All-Sky Monitor (2-12 keV) of the Rossi X-ray Timing Explorer satellite (RXTE) in two consecutive 90-second dwells beginning at 18 August 1998 08:40 UT. The source was detected at fitted count rates of 45 and 15 cts/sec (per SSC), respectively, with uncertainties of ~3 cts/sec for each. Examination of the multiple time series data for these dwells indicates that the dramatic difference in count rates is likely due to a strong flare event (probably a type II burst) that began 10 seconds after the start of the first dwell, and was decaying away by the start of the second.

Subsequent observation with the RXTE Proportional Counter Array (2-60 keV) on 19 August, beginning at 05:00 UT, found the source in a state of dramatic variability. 100-200 second long plateau-like type II bursts of ~13,000 cts/sec (~1 Crab) peak count rate were superposed on ~1000 cts/sec persistent emission. The second type II burst observed showed strong (10-15% rms) 2-3 Hz QPO on its plateau; the persistent emission also exhibited strong QPO -- in the ~0.04 Hz (following a burst), 2-4 Hz (between bursts) and ~0.4 Hz (preceding the bursts) frequency ranges -- and showed pronounced ``dips'' prior to and following the bursts.

The observation of type II bursts at this early stage of the outburst is contrary to the expectations of Guerriero et al. (1998); however, we note that these authors did not have access to any observations that occurred within a day of the outburst start. It is thus possible that this is how every outburst of the source begins. It is also possible, however, that we are witnessing a new type of Rapid Burster outburst that has not been seen with RXTE before.

If the subsequent evolution of the outburst occurs as Guerriero et al. (1998) describe, then regular, rapid type II bursting will commence on or about 8 September, and last for roughly 12 days. High time resolution (<10 sec) infrared observations of the source during this time are eagerly sought; the IR counterparts to the type II X-ray bursts are expected to reach K~16.5 or brighter. Please contact the authors to arrange possible coordination with RXTE observations. (See also the Rapid Burster Page.)

The onset of this outburst occurred 201 days after the onset of the previous outburst, consistent with an average 216+/-16 day recurrence time for all outbursts since the launch of RXTE. The four preceding Rapid Burster outbursts began on 13 April 1996, 29 October 1996, 25 June 1997, and 28 January 1998, respectively.

The coordinates of the Rapid Burster's (likely) VLA counterpart (IAUC # 6813 ; ATEL #8) are RA=17h33m24s.61; Dec=-33d23m19s.8 (J2000).

Rapid Burster Page