V 0332+53 sets out slowly this time, will it ride fast?

ATel #7822; Victor Doroshenko (IAAT), Sergey Tsygankov (Tuorla Observatory), Carlo Ferrigno (ISDC), Enrico Bozzo (ISDC), Alexander Lutovinov (IKI RAS), Alexander Mushtukov (Tuorla Observatory)
on 22 Jul 2015; 07:54 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Alexander Lutovinov (aal@hea.iki.rssi.ru)

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Renewed X-ray and optical activity from transient Be X-ray binary V 0332+53 reported recently (Atel #7682, #7685) suggests that current outburst is likely a giant one. The Swift BAT light curve of the source shows that it is brightening steadily since ~30 days. The source flux is now approaching 0.8 Crab in the Swift/BAT energy band and continues to increase. The rise time of the current outburst would be already comparable to that during the giant outburst in 2005. However, the currently observed flux level was reached in just 5-10 days on that occasion (see accompanying URL where historic RXTE/ASM light curves are scaled to the Swift BAT count rate using the overlapping data). This suggests either the lower magnitude of the current outburst, or its longer overall duration. In the later case the source might still be far from the outburst peak, which might correspond to significantly higher flux than in previous outbursts.

We note that the giant outburst in 2005 had factor of two longer rise time than the normal outburst in 2008 and reached factor of 16 higher peak flux. As the current outburst seems to be characterized by rising time that is factor of five and ten slower than previous giant and normal outbursts, we expect that the peak flux will be significantly higher than the one measured in 2005 (if the source follows same pattern as in previous outbursts and does not start to decay within next several days).

We strongly encourage X-ray and optical monitoring of the source as well as X-ray observations at the outburst peak.

V0332+53 light curves