SMC X-ray source SXP85.4 is revealed to be the same source as SXP91.1
ATel #3396; M. J. Coe (Southampton University), E. S. Bartlett (Southampton), A. J. Bird (Southampton), R. H.D. Corbet (UMBC/NASA GSFC), S. Drave (Southampton) and L. J. Townsend (Southampton)
on 2 Jun 2011; 11:19 UT
Credential Certification: Malcolm Coe (mjcoe@soton.ac.uk)
Subjects: X-ray, Binary, Neutron Star, Transient, Pulsar
Following on the report of a proposed new Be/X-ray binary pulsar system in the SMC (ATel #2813), an INTEGRAL ToO observation was carried out on 20 May 2011 after RXTE had detected the source again on 13 May 2011. The INTEGRAL observations revealed a clear source in the JEM-X detectors at RA,Dec (2000)=(12.727,-72.237) with a significance of 4.7 sigma and an uncertainty of a few arcminutes. This position is consistent with a previously known Be/X-ray system SXP91.1 which we believed had not been detected in our RXTE monitoring of the SMC for several years. However, comparison of the pulse period history of the two sources provides a coherent story of continuous spin up over more than a decade, see
figure
. Furthermore the recent X-ray outburst history seen in our RXTE data in the last year indicates a binary period of approximately 88d which is consistent with the reported optical modulation seen on the OGLE III data from the optical counterpart to SXP91.1 (Schmidtke et al AJ 127, 3388 (2004)).
We therefore conclude that SXP85.4 = SXP91.1.
We are grateful to the INTEGRAL project for permitting & scheduling a ToO observation that helped resolve this ambiguity.
