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

被引:37
作者
Carpano, S.
Pollock, A. M. T.
Prestwich, A.
Crowther, P.
Wilms, J.
Yungelson, L.
Ehle, M.
机构
[1] ESA, ESAC, XMN Newton Sci Operat Ctr, Madrid 28080, Spain
[2] Harvard Smithsonian Ctr Astrophys, Cambridge, MA 02138 USA
[3] Univ Sheffield, Dept Phys & Astron, Sheffield S3 7RH, S Yorkshire, England
[4] FAU Erlangen Nurnberg, Dr Remeis Observ, Inst Astron, D-96049 Bamberg, Germany
[5] Russian Acad Sci, Inst Astron, Moscow 119017, Russia
关键词
X-rays : individuals : NGC 300 X-1; X-rays : binaries; stars : Wolf-Rayet;
D O I
10.1051/0004-6361:20077363
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
Context. NGC 300 X-1 is the second extragalactic candidate, after IC 10 X-1, in the rare class of Wolf-Rayet/compact object X-ray binary systems exemplified in the Galaxy by Cyg X-3. From a theoretical point of view, accretion onto a black hole in a detached system is possible for large orbital periods only if the mass of the relativistic object is high or the velocity of the accreted wind is low. Aims. We analysed a 2 week SWIFT XRT light curve of NGC 300 X-1 and searched for periodicities. Methods. Period searches were made using Lomb-Scargle periodogram analysis. We evaluated the confidence level using Monte Carlo simulations. Results. A period of 32.8 +/- 0.4 h (3 sigma error) was found for NGC 300 X-1 with a confidence level > 99%. Furthermore, we confirm the high irregular variability during the high flux level, as already observed in the XMM-Newton observations of the source. A folded XMM-Newton light curve is shown, with a profile that is in agreement with SWIFT. The mean absorbed X-ray luminosity in the SWIFT observations was 1.5 x 10(38) erg s(-1), close to the value derived from the XMM-Newton data. Conclusions. While Cyg X-3 has a short period of 4.8 h, the period of NGC 300 X-1 is very close to that of IC 10 X-1 (34.8 +/- 0.9 h). These are likely orbital periods. Possibility of formation of accretion disk for such high orbital periods strongly depends on the terminal velocity of the Wolf-Rayet star wind and black-hole mass. While low masses are possible for wind velocities <= 1000 km s(-1), these increase to several tens of solar masses for velocities > 1600 km s(-1) and no accretion disk may form for terminal velocities larger than 1900 km s(-1).
引用
收藏
页码:L17 / L20
页数:4
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