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ATEL # 994; P. Romano (IANF-OABrera), L. Sidoli (INAF-IASF Milano), V. Mangano (INAF-IASF Palermo)
on 8 Feb 2007; 13:20 UT
Distributed as an Instant Email Notice (Request for Observations)
Password Certification: Pat Romano (firstname.lastname@example.org)
Subjects: X-ray, Request for Observations, Binaries, Transients
Referred to by ATEL #: 995
IGR J11215-5952 is the first member of the new class of Supergiant Fast X-ray Transients which displays periodic outbursts, with a recurrence time of 329 days (Sidoli et al. 2006,A&A,450,L9; Smith et al.2006,ATEL #766), likely indicative of the orbital period of the binary system.
Based on this periodicity, we are performing a monitoring of the source field with Swift/XRT during the times around the fifth outburst, expected to occur on February 8-10.
Two 2-ks pointings were performed on February 4 and February 5 (see linked table) which resulted in only 3-sigma upper limits (count rate <6E-03, and <6E-03 counts/s, respectively, in the 1-10keV energy band). The first observations of marginal detection were performed on February 6 where a count rate of 3.507E-03 +/- 1.9E-03 counts/s (S/N=1.9, 1-10keV) was observed. Observations performed on February 7 and 8 yielded firmer detections.
A clear renewed flaring activity is observed starting on February 7-8 when the source was observed with a signal to noise ratio of 2.93, after 328 days from the latest outburst occurred on 2006, March 16, fully confirming the periodicity of the outbursts, with a count rate of (1.06+/-0.36)E-02 counts/s. This translates into about (1.3+/-0.5) E-12 ergs/cm2/s (1-10 keV, correcting for the absorption and assuming a spectral shape similar to the one observed in March 2006).
The best-fit position of the X-ray source is RA(J2000)=11 21 46.7 Dec(J2000)=-59 51 38.5, with an estimated uncertainty of 7 arcsec. This position is consistent (<4 arcsec) with the one obtained in March 2006 (Steeghs et al.2006, ATEL #768).
We would like to thank the Swift Team for making these observations possible, in particular N. Gehrels, the duty scientists M. Chester, J. Kennea, and C. Gronwall, as well as the science planner C. Pagani.
Swift/XRT First Observations of IGR J11215-5952