Detection of an X-ray outburst by INTEGRAL from a previously unknown SMC source IGR J01217-7257

ATel #5806; M. J. Coe (Southampton University), A. J. Bird (Southampton University), V. A. McBride (UCT/SAAO), E. S. Bartlett (UCT), L. J. Townsend (UCT), F. Haberl (MPE), J. Kennea (PSU) and A. Udalski (Warsaw).
on 24 Jan 2014; 16:27 UT
Credential Certification: Malcolm Coe (mjcoe@soton.ac.uk)

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INTEGRAL observations of the Small Magellanic Cloud on 11 January 2014 detected a bright X-ray source in the Wing of the SMC which we identify as IGR J01217-7257. The best position determined from JEM-X is 01 21 40.6, -72 57 21.9 with an uncertainty of 1.5 arcmins. The IBIS flux was 0.92 +/- 0.16 counts/s. Near the centre of this error circle is a 14th magnitude star identified in OGLE IV as SMC732.03.3540 (position 01 21 40.6, -72 57 31). This star shows dramatic large brightness changes of the order of one optical magnitude on timescales of 5-6 years. It is currently in a bright state and shows strong clear outbursts every 84d, the most recent consistent in time with our INTEGRAL detection. When it was last in a similar bright state 9-10 years ago the same outburst features were apparent. We identify the 84d as the binary period of the system. The nearest catalogued Be/X-ray pulsar system on the sky is SXP2.16 (Corbet et al 2003 IAUC 8064 ) which was detected by RXTE in 2003. The position of this source is poorly defined due to the non-imaging characteristics of the RXTE/PCA instrument. Attempts to locate it using RXTE to scan across the region resulted in a position formally inconsistent with that of IGR J01217-725. However, we do note that the time of the RXTE detection coincided with a previous optical flare and a general increased optical brightness of SMC732.03.3540. To confirm or refute the identification of IGR J01217-7257 with SXP2.16 we carried out a Swift/WT observation pointed at SMC732.03.3540 which detected a strong X-ray signal, but no evidence for any X-ray pulsations in the 1.5s - 300s range. We therefore cannot link IGR J01217-7257 with SXP2.16 using a pulse signature. A 1ks Swift XRT image was obtained on 24 January 2014. It reveals a single weak source located at 01 21 41, -72 57 33 with an uncertainty of 4 arcseconds. This position is consistent with that of the IBIS and the OGLE optical counterparts. Hence we conclude that IGR J01217-7257 is likely to be a new Be/X-ray binary system. We are grateful to Swift for its rapid and positive response to our requests for help in identifying this system.

OGLE IV lightcurve of IGR J01217-7257