XMM-Newton discovery of X-ray pulsations from RX J0032.9-7348 (= SXP 7.02)
ATel #16901; F. Haberl (MPE), G. Vasilopoulos (NKUA), P. Maggi (Universite de Strasbourg), C. Maitra, D. Kaltenbrunner, A. Rau (MPE), L. Ducci (IAAT Tuebingen), I. Kreykenbohm, P. Weber, J. Wilms (Remeis-Observatory/ECAP, FAU Erlangen), A. Udalski (Warsaw University Observatory), H. Cheng (NAO, CAS), Q. Liu (THU), S. Jiang, W. Zhang (NAO, CAS), L. Tao, H. Feng, P. Li (IHEP, CAS), N. Rea (ICE-CSIC, IEEC), C. Jin, W. Yuan (NAO, CAS)
on 11 Nov 2024; 22:21 UT
Credential Certification: Frank Haberl (fwh@mpe.mpg.de)
Subjects: Binary, Neutron Star, Star, Transient, Pulsar
An X-ray brightening of a source likely associated with the Be X-ray binary candidate RX J0032.9-7348 in the SMC (Kahabka, Pietsch 1996, A&A 312, 919) was recently discovered with the Einstein Probe mission (EP, ATel#16880).
We triggered one of our anticipated target of opportunity (TOO) observations with XMM-Newton, which was performed on November 2, 2024.
We obtained about 12 ks of exposure with low background. The derived X-ray source position of
RA (J2000) = 00:32:53.61, DEC (J2000) = -73:48:31.5 is within 0.6" of the Gaia DR3 position (RA = 00:32:53.57, DEC = -73 48 32.136) of the B0.5V star proposed as one of two possible optical counterparts (GSC 0914101338 = star 2 in Stevens et al. 1999, MNRAS 309, 421).
This ~15.8 mag star is consistent with OGLE SMC714.27.8326 which has been monitored by OGLE for more than 23 years. In the I band the system shows variability, with a flat baseline emission around 15.87 mag, and two major brightening events, with durations of ~1000 d and ~500 d and peak magnitudes of 15 and 14.8 mag respectively. During these events the V-I color of the system became significant redder, evolving from -0.2 to 0.2 mag.
A preliminary timing analysis of the EPIC data revealed X-ray pulsations at a fundamental period of 7.02475(4)s with two harmonics. The EPIC spectra can be modelled with an absorbed powerlaw with photon index 1.0. The average observed 0.2 - 10 keV flux was 4.2×10-11 erg cm-2 s-1 and the absorption-corrected luminosity 2.1×1037 erg s-1 (0.2-10.0 keV, assuming a distance of 62 kpc), a somewhat lower brightness level as during the EP observations five days earlier.
