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

Abstract

The examination of two 2010 Chandra ACIS 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-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 fit 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 WolfRayet plus black hole 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 .

Hierarchical black hole triples in young star clusters: impact of Kozai–Lidov resonance on mergers

“…From the results of Table 2 we can determine the merger rate for BH-BH binaries using a Drake-like equation (Esposito et al 2015): simulated SC (= 100 Myr), fSF is the fraction of star formation that occurs in SCs (=0.8 from Lada & Lada 2003), nSC is the number of simulated SCs, MSC is the average mass of the SCs (= 3500 M⊙), andtGW,i is the effective coalescence timescale of the i-th binary, as given by equation 5.…”

XMM–Newtondiscovery of mHz quasi-periodic oscillations in the high-mass X-ray binary IGR J19140+0951

“…Indeed, a signal at a similar period (∼5.9 ks) was discovered by the detection algorithm of the Chandra ACIS Timing Survey (CATS) project 1 during an authomatic search of the same data set (Israel et al, submitted; see also Esposito et al 2013Esposito et al , 2015. Fig.…”

Formation channels of single and binary stellar-mass black holes

“…Since | ṁ1 | is usually quite low (| ṁ1 | < 10 −3 M yr −1 ) and v w is usually quite high (> 1000 km s −1 for a line-driven wind) with respect to the orbital velocity, this kind of mass transfer is usually rather inefficient. However, most of the observed high-mass X-ray binaries [352,353] and in particular all the systems with a WR star companion [112] are wind-fed systems. Mass transfer by Roche lobe overflow is usually more efficient than wind accretion.…”