A new transient X-ray pulsar in the Small Magellanic Cloud
ATel #5552; G. L. Israel (INAF-OARoma), P. Esposito (INAF-IASF Mi), V. D'Elia (ASI ASDC), L. Sidoli (INAF-IASF Mi) on behalf of a larger collaboration
on 6 Nov 2013; 16:12 UT
Credential Certification: Paolo Esposito (paoloesp@iasf-milano.inaf.it)
Subjects: X-ray, Binary, Neutron Star, Pulsar
Referred to by ATel #: 5556
Within the CATS @ BAR project (see Esposito et al. 2013, MNRAS, 433, 2028) we discovered a new transient X-ray pulsar in Chandra archival data (obs.ID 15504) of the Small Magellanic Cloud (SMC), CXOU J005758.4-721620.
This source is separated by ~5.5 arcmin by the new INTEGRAL source IGR J00569-7226 (ATEL #5547), so the two sources are unrelated.
During the Chandra observation 15504, carried out on 2013 September 06 (exposure: 48.8 ks), the X-ray spectrum of CXOU J005758.4-722229 could be well fit by a power-law model with photon index 0.3+\-0.1 (1sigma c.l.). The corresponding 1-10 keV observed (pile-up corrected) flux was about 10^-12 ergs/s/cm^2. We detected strong coherent pulsations (pulsed fraction: ~50%) at a period of P = 7.91807(1)s. The Chandra position (RA = 00:57:58.4 and Dec = -72:22:29.5, J2000, 1.5" radius accuracy) is consistent with a variable V = 16 mag object in the OGLE catalog (Mennickent et al. 2002, A&A, 393, 887).
The source was already catalogued as a faint ROSAT HRI X-ray source by Sasaki et al. 2000 (A&AS, 147, 75). Previous XMM-Newton, Chandra and ROSAT observations indicate substantial flux variability in this object, though no pulsations is detected. The X-ray properties similar to those of many other Be X-ray binaries discovered in the SMC and the OGLE counterpart suggest a Be X-ray binary pulsar nature for CXOU J005758.4-722229. This would be the second source of this kind discovered by the CATS @ BAR search in the SMC after the 292-s CXOU J005047.9-731817 (Esposito et al. 2013, MNRAS, 433, 3464).
Optical follow-up observations are in progress.
