S-CUBED confirmation of 22.3 day orbital period of XMMU J010429.4-723136 / SXP 164
ATel #14982; Jamie A. Kennea (Penn State), Malcolm J. Coe (Southampton) and Phil A. Evans (Leicester)
on 18 Oct 2021; 14:53 UT
Credential Certification: Jamie A. Kennea (kennea@astro.psu.edu)
Subjects: X-ray, Binary, Neutron Star, Pulsar
The BeXRB XMMU J010429.4-723136 was recently reported by Carpano et al (arXiv:2106.14536) to have a 164s pulsar period in eROSITA observations, and was therefore named SXP 164. We note that this source was previously erroneously known as SXP 707 (ATEL #3154), however the 707s period was in fact the dithering period of Chandra (ATEL #5674).
Carpano et al. also report a new analysis of OGLE data, reporting the detection of a 22.35+/-0.11 day period, which they suggest to be the orbital period of SXP 164.
We have analyzed over 5 years of data from S-CUBED, the Swift SMC Survey (Kennea et al, 2018), in order to search for any signature of this orbital period in X-ray data. We note that although S-CUBED has a weekly cadence, the long baseline of observations make detection of relatively short orbital periods possible.
Performing a Lomb-Scargle analysis on the S-CUBED X-ray data searching over periods in the range 7 to 100 days, we the detect strongest a peak in the periodogram to be at 22.34 days, with a false alarm probability of 0.02%.
This period is in good agreement with the OGLE measured value reported by Carpano et al. The detection of this period in S-CUBED data is likely the signature of repeated Type I outbursts from this BeXRB, which are expected to repeat once per orbit. Therefore we confirm the 22.3 day orbital period of SXP 164 reported by Carpano et al.
