Flux and spectral variations in the Circinus Galaxy

Bianchi, S.; Matt, Giorgio; Fiore, F.; Fabian, A. C.; Iwasawa, K.; Nicastro, F.

doi:10.1051/0004-6361:20021414

Cited by 37 publications

(55 citation statements)

References 24 publications

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“…In literature, CG X-1 is generally considered to be an ULX in the CG (e.g. Bianchi et al 2002;Swartz et al 2004;Liu & Mirabel 2005;Ptak et al 2006;Berghea et al 2008;Gladstone et al 2013). …”

Section: The Controversial Source Cg X-1mentioning

confidence: 99%

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

Esposito¹,

Israel²,

Milisavljević³

et al. 2015

Mon. Not. R. Astron. Soc.

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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 .

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Section: The Controversial Source Cg X-1mentioning

confidence: 99%

“…The X-ray luminosity of CG X-1 is variable by a factor of ≈10 (Bianchi et al 2002;Weisskopf et al 2004). The highest flux reported in literature (5.2×10…”

mentioning

confidence: 96%

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

Esposito¹,

Israel²,

Milisavljević³

et al. 2015

Mon. Not. R. Astron. Soc.

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“…Previous detections of the Compton shoulder are unresolved (see, e.g., Molendi, Bianchi, & Matt 2003), and in many cases, they are statistically marginal as well (Iwasawa, Fabian, & Matt 1997;Matt & Guainazzi 2003). The high spectral resolution of 33 eV (FWHM) at 6.4 keV attained by the High Energy Transmission Grating Spectrometer (HETGS) (Canizares et al 2000) on board the Chandra X-Ray Observatory (Weisskopf et al 2000) enables us, for the first time, to resolve the Compton shoulder of the iron Ka line (see, e.g., Kaspi et al 2002;Bianchi et al 2002).…”

Section: Introductionmentioning

confidence: 99%

Detection of a Fully Resolved Compton Shoulder of the Iron K Line in the Chandra X-Ray Spectrum of GX 301-2

Watanabe

Šako

Ishida

et al. 2003

ApJ

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We report the detection of a fully resolved, Compton-scattered emission line in the X-ray spectrum of the massive binary GX 301Ϫ2 obtained with the High Energy Transmission Grating Spectrometer on board the Chandra X-Ray Observatory. The iron Ka fluorescence line complex observed in this system consists of an intense narrow component centered at an energy of keV and a redward shoulder that extends down E p 6.40 to ∼6.24 keV, which corresponds to an energy shift of a Compton backscattered iron Ka photon. From detailed Monte Carlo simulations and comparisons with the observed spectra, we are able to directly constrain the physical properties of the scattering medium, including the electron temperature and column density, as well as an estimate for the metal abundance.

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“…A ULX candidate in the Circinus galaxy ( = 14 h 13 m 12F3, = À65 20 0 13 00 [J2000.0], hereafter CG X-1) appears to be periodic with a period of 27 AE 0:7 ks (Bauer et al 2001;Bianchi et al 2002). Furthermore, at times there is a sharp deep dip in the X-ray light curve reminiscent of eclipses (Weisskopf 2004;Fig.…”

Section: Introductionmentioning

confidence: 99%

On the Nature of the Bright Short‐Period X‐Ray Source in the Circinus Galaxy Field

Weisskopf

Tennant

et al. 2004

ApJ

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The spectrum and light curve of the bright X-ray source CG X-1 in the field of the Circinus galaxy are reexamined. Previous analyses have concluded that the source is an accreting black hole of mass k50 M , although it has been noted that the light curve resembles that of an AM Herculis system. Here we show that the short period and an assumed main-sequence companion constrain the mass of the companion to less than 1 M . Furthermore, a possible eclipse seen during one of the Chandra observations and a subsequent XMM-Newton observation constrain the mass of the compact object to less than 60 M . If such a system lies in the Circinus galaxy, then the accreting object must either radiate anisotropically or strongly violate the Eddington limit. Even if the emission is beamed, then the companion star that intercepts this flux during eclipse will be driven out of thermal equilibrium and evaporate within $10 3 yr. We find that the observations cannot rule out an AM Herculis system in the Milky Way and that such a system can account for the variations seen in the light curve.

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Flux and spectral variations in the Circinus Galaxy

Cited by 37 publications

References 24 publications

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

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

Detection of a Fully Resolved Compton Shoulder of the Iron K Line in the Chandra X-Ray Spectrum of GX 301-2

On the Nature of the Bright Short‐Period X‐Ray Source in the Circinus Galaxy Field

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