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A 33 hour period for the Wolf-Rayet/black hole X-ray binary candidate NGC 300 X-1

ATEL # 974; S. Carpano (ESA), A. Pollock (ESA), A. Prestwich (SAO), P. Crowther (Univ. of Sheffield), L. Yungelson (INASAN, Moscow), J. Wilms (Univ. of Bamberg), M. Ehle (ESA)
on 9 Jan 2007; 18:13 UT
Password Certification: Andrea Prestwich (

Subjects: X-ray, Binaries, Black Holes

NGC 300 X-1 is the second extragalactic candidate, after IC 10 X-1, for the rare class of Wolf-Rayet/compact object X-ray binary system (Carpano et al. 2007, A&A, 461,9L) uniquely exemplified in the Galaxy by Cyg X-3. From a theoretical point of view, these systems should have orbital periods up to several tens of hours (Ergma & Yungelson, 1998, A&A, 333, 151; Lommen et al., 2005, A&A, 443, 231L). While Cyg X-3 has a short period of 4.8 hour, a longer period of 34.8+-0.9 hour has recently been found for IC10 X-1 (Prestwich et al., ATel #955). The 4 XMM-Newton observations of NGC 300 X-1 between 2000 and 2006 considered by Carpano et al. lasted for about 11 hour each, during one of which the source increased in flux by a factor of 10 within 10 hour. Thanks to SWIFT TOO observations analysed using a Lomb-Scargle periodogram method, a period of 33.05 hour (>99.9% confidence level) has been found for NGC 300 X-1, a value very close to that of IC 10 X-1. We think that these are likely to be orbital periods. The SWIFT lightcurve is given below. A paper showing the results is in preparation by Carpano et al. We warmly thank Neil Gehrels and Dave Burrows for approving the SWIFT observing time.

SWIFT Light Curve of NGC 300 X-1

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