SMC X-3 - an exceptionally bright extended outburst
ATel #9677; M. J. Coe (Southampton), J. A. Kennea (PSU), L. J. Townsend (UCT), V. McBride (UCT/SAAO), P. A. Evans (Leicester) and A. Udalski (Warsaw)
on 27 Oct 2016; 14:18 UT
Credential Certification: Malcolm Coe (mjcoe@soton.ac.uk)
Subjects: Optical, X-ray, Binary, Neutron Star, Transient
Referred to by ATel #: 9731
As a result of the detection of the Be/X-ray binary SMC X-3 having entered an outburst phase by S-CUBED (Kennea et al., ATEL #9362) and MAXI (Negoro et al., ATEL #9348), on August 10 2016 Swift began a series of Target of Opportunity observations (Kennea et al., ATEL #9370). These observations are continuing and have revealed that this Be/X-ray system is undergoing a major Type II outburst - possibly the largest ever recorded from such a system.
The outburst has, so far, lasted over two months and S-CUBED XRT monitoring revealed it peaked at an X-ray luminosity of 8 x 10E38 erg/s (assuming a distance of 62kpc) on 25 August. The most recent measurements on 20 October 2016 put the flux at a factor of 20 less and steadily declining. Throughout this period, the optical I-band flux measured by OGLE has revealed the companion Be star to be in an exceptionally bright phase, peaking at I=14.4.
During the vast majority of the outburst we measure a steady spin up in the 7.8s pulse period of the neutron star from Swift/WT measurements, but about October 14-15 the sign of P_dot reversed and the source is now showing a steady spin down - indicating a possible torque reversal event. Around the same time the optical I-band flux exhibited a secondary outburst peak instead of simply continuing a steady decline.
We will continue to monitor the system at X-ray and optical wavelengths (both photometry & spectroscopy) and report further developments in the literature.
