Follow-up Swift observations of SMC X-3 during its Type II outburst: no torque reversal yet
ATel #9731; Shan-Shan Weng (NJNU, IHEP), Ming-Yu Ge (IHEP), Hai-Hui Zhao (NJNU), Wei Wang (NAOC), Shuang-Nan Zhang (IHEP, NAOC)
on 8 Nov 2016; 01:37 UT
Credential Certification: Shan-Shan Weng (wengss@ihep.ac.cn)
Subjects: X-ray, Binary, Neutron Star, Transient, Pulsar
The Be/X-ray binary SMC X-3 started a Type II outburst around 2016 July 30 (ATEL #9348 and #9362), and the outburst has been monitored with Swift since 2016 August 10. The observed spin frequency increased smoothly before October 14-15, after then it decreased with time (Coe et al., ATEL #9677). After correcting for its orbital modulation (P_orb = 44.92 day, Bird et al. 2012), we find that the corrected spin frequency has increased steadily from 128.02 mHz (on August 10), and currently the frequency derivative is close to zero (f ~ 128.66 mHz, L_x ~ 7x10^37 erg/s); thus, we expect to see a torque reversal soon if its luminosity continues to decrease in the following observations. Additionally, the change rate of its spin frequency is tightly correlated with the X-ray flux. Its pulse profiles changed dramatically and generally showed double peaks during the outburst, but now tends to merge into a single peak as its flux decays. We encourage further multi-wavelength coverage for investigating the transition from a super-critical to a sub-critical accretion in this BeXB.