Details

Autor(en) / Beteiligte

• Esposito, P
• Israel, G. L
• Milisavljevic, D
• Mapelli, M
• Zampieri, L
• Sidoli, L
• Fabbiano, G
• Rodríguez Castillo, G. A

Titel

Periodic signals from the Circinus region: two new cataclysmic variables and the ultraluminous X-ray source candidate GC X-1

Ist Teil von

• Monthly notices of the Royal Astronomical Society, 2015-09, Vol.452 (2), p.1112-1127

Ort / Verlag

London: Oxford University Press

Erscheinungsjahr

2015

Link zum Volltext

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• 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 ≈1.1 × 10−13 erg cm−2 s−1 (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−1 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 yr−1.