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|Title:||Periodic signals from the Circinus region: two new cataclysmic variables and the ultraluminous X-ray source candidate GC X-1||Authors:||Esposito, P.
ISRAEL, Gian Luca
RODRIGUEZ CASTILLO, Guillermo Andres
|Issue Date:||2015||Journal:||MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY||Number:||452||Issue:||2||First Page:||1112||Abstract:||The examination of two 2010 Chandra ACIS (Advanced CCD Imaging Spectrometer) exposures of the Circinus galaxy resulted in the discovery of two pulsators: CXO J141430.1-651621 and CXOU J141332.9-651756. We also detected 26 ks pulsations in CG X-1, consistently with previous measures. For ̃40 other sources, we obtained limits on periodic modulations. In CXO J141430.1-651621, which is ̃2 arcmin outside the Circinus galaxy, we detected signals at 6120 ± 1 s and 64.2 ± 0.5 ks. In the longest observation, the source showed a flux of abut 1.1 × 10^-13 erg/cm^2/ (absorbed, 0.5-10 keV) and the spectrum could be described by a power law with photon index Γ ≃ 1.4. From archival observations, we found that the luminosity is variable by ≈50 per cent on time-scales of weeks to years. The two periodicities pin down CXO J141430.1-651621 as a cataclysmic variable of the intermediate polar subtype. The period of CXOU J141332.9-651756 is 6378 ± 3 s. It is located inside the Circinus galaxy, but the low absorption indicates a Galactic foreground object. The flux was ≈5 × 10^-14 erg/cm^2/s in the Chandra observations and showed ≈50 per cent variations on weekly/yearly scales; the spectrum is well fitted by a power law with Γ ≃ 0.9. These characteristics and the large modulation suggest that CXOU J141332.9-651756 is a magnetic cataclysmic variable, probably a polar. For CG X-1, we show that if the source is in the Circinus galaxy, its properties are consistent with a Wolf-Rayet (WR) plus black hole (BH) binary. We consider the implications of this for ultraluminous X-ray sources and the prospects of Advanced LIGO and Virgo. In particular, from the current sample of WR-BH systems, we estimate an upper limit to the detection rate of stellar BH-BH mergers of ̃16 y^-1.||Acknowledgments:||This research is based on data obtained from the Chandra Data Archive and has made use of software provided by the Chandra X-ray Center (CXC) in the application package ciao and sherpa . This research has also made use of data obtained from the ESA's XMM–Newton Science Archive (XSA) and from the ESO Science Archive Facility (under request number 161735), and of the NED, which is operated by the JPL, Caltech, under contract with the NASA. The iraf software is distributed by the NOAO, which is operated by AURA, Inc., under cooperative agreement with the NSF. PE acknowledges a Fulbright Research Scholar grant administered by the US–Italy Fulbright Commission and is grateful to the Harvard–Smithsonian Center for Astrophysics for hosting him during his Fulbright exchange. MM acknowledges financial support from the MIUR through grant FIRB 2012 RBFR12PM1F, and from INAF through grants PRIN-2011-1 and PRIN-2014-14. LZ acknowledges financial support from the ASI/INAF contract no. I/037/12/0. LS acknowledges the PRIN-INAF 2014 grant ‘Towards a unified picture of accretion in High Mass X-Ray Binaries’. PE thanks M. Mezcua for surveying the available HST data of the Circinus region and A. Wolter for comments on the manuscript.||URI:||http://hdl.handle.net/20.500.12386/26270||URL:||https://academic.oup.com/mnras/article/452/2/1112/1063525||ISSN:||0035-8711||DOI:||10.1093/mnras/stv1379||Bibcode ADS:||2015MNRAS.452.1112E||Fulltext:||open|
|Appears in Collections:||1.01 Articoli in rivista|
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