Detection of mHZ QPOs in BeXRB pulsar XTE J0111.2-731 (SXP 31.0) in SMC
ATel #17204; Kinjal Roy (RRI), Rahul Sharma (IUCAA), Hemanth Manikantan (INAF), Biswajit Paul (RRI)
on 24 May 2025; 09:53 UT
Credential Certification: Kinjal Roy (kinjal@rrimail.rri.res.in)
Subjects: X-ray, Binary, Neutron Star, Transient, Pulsar
The Be/X-ray Binary system XTE J0111.2-7317 or SXP 31.0 has been detected by Swift (ATel: #17147) and SRG/ART-XC (ATel: #17163) during its latest outburst. NuSTAR made a TOO observation of the source between 2nd and 3rd May 2025 (MJD: 60797-60798). The source was detected with NuSTAR with a count rate of about 7 counts/s in FPMA and FPMB modules. Assuming the distance to the SMC to be 60 kpc, we estimated the luminosity of the source to be 2x10^38 erg/s in the 3-79 keV energy band. Pulsations were present in the entire lightcurve with a period of about 30.4497(1) sec, consistent with the ASCA observation of the 1998 outburst (Yokogawa et al. 2000). A quasi-periodic oscillation (QPO) was discovered in the source at 1.27 Hz with RXTE/PCA data during the declining phase of the 1998 outburst (Kaur et al. 2007).
In the current NuSTAR data, the 1.27 Hz QPO was not detected; instead, a low-frequency QPO was detected at 0.8 +/- 0.1 mHz. The quasi-periodic oscillation has a Q factor of about 2.7. The QPO was visible in the NuSTAR light curve. The durations of successive QPO cycles showed gradual changes and not a stochastic behavior, indicating some physical processes driving the cycle durations.
