Partial Covering during Long-Term Dips in Circinus X-1

We present the results of simultaneous X‐ray and radio observations of the peculiar Z‐type neutron star X‐ray binary Cir X‐1, observed with the Rossi X‐ray Timing Explorer satellite and the Australia Telescope Compact Array in 2000 October and 2002 December. We identify typical Z‐source behaviour in the power density spectra as well as characteristic Z patterns drawn in an X‐ray hardness–intensity diagram. Power spectra typical of bright atoll sources have also been identified at orbital phases after the periastron passage, while orbital phases before the periastron passage are characterized by power spectra that are typical neither of Z nor of atoll sources. We investigate the coupling between the X‐ray and the radio properties, focusing on three orbital phases when an enhancement of the radio flux density has been detected, to test the link between the inflow (X‐ray) and the outflow (radio jet) to/from the compact object. In two out of three cases, we associate the presence of the radio jet to a spectral transition in the X‐rays, although the transition does not precede the radio flare, as detected in other Z sources. An analogous behaviour has recently been found in the black hole candidate GX 339‐4. In the third case, the radio light curve shows a similar shape to the X‐ray light curve. We discuss our results in the context of jet models, considering also black hole candidates.

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“…Dips are also present when close to phase 0.0 (2000 October 19; 2002 December 3, 4 and 5) as previously reported (e.g. Ding, Qu & Li 2006).…”

Section: Results and Interpretationsupporting

confidence: 86%

Linking jet emission and X-ray properties in the peculiar neutron star X-ray binary Circinus X-1

Soleri

Tudose

Fender

et al. 2009

Monthly Notices of the Royal Astronomical Society

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“…Neither recent claims of soft excesses (Iaria et al 2005) nor unabsorbed soft components (Ding et al 2006) can be substantiated in our high-resolution spectra during the low-flux state here and in the high-flux state years ago (see also SB02; Galloway et al 2007), and any claims referring to the angle of inclination likely do not apply. In Ding et al (2006) it was suggested that this excess could come from the accretion hot spot, and its large emission volume would then rule out a large inclination. However, the spectral analysis presented seems clearly tainted by an unrealistically high Fe K line flux.…”

mentioning

confidence: 55%

The Variable Warm Absorber in Circinus X‐1

Schulz

Kallman

Brandt

2008

ApJ

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We observed Circinus X-1 twice during a newly reached low-flux phase near zero orbital phase using the HighEnergy Transmission Grating Spectrometer (HETGS) onboard Chandra. In both observations the source did not show the P Cygni lines we observed during the high-flux phases of the source in 2000 and 2001. During the prezero phase the source did not exhibit significant variability but did exhibit an emission-line spectrum rich in H-and He-like lines from high-Z elements such as Si, S, Ar, and Ca. The light curve in the postdip observation showed quiescent and flaring episodes. Only in these flaring episodes was the source luminosity significantly higher than observed during the prezero phase. We analyzed all high-resolution X-ray spectra by fitting photoionization and absorption models from the most recent version of the XSTAR code. The prezero-phase spectrum could be fully modeled with a very hot photoionized plasma with an ionization parameter of log ¼ 3:0, down from log ¼ 4:0 in the high-flux state. The ionization balances we measure from the spectra during the postzero-phase episodes are significantly different. Both episodes feature absorbers with variable high columns, ionization parameters, and luminosity. While cold absorption remains at levels quite similar to that observed in previous years, the new observations show unprecedented levels of variable warm absorption. The line emissivities also indicate that the observed low source luminosity is inconsistent with a static hot accretion disk corona (ADC), an effect that seems common to other near-edge-on ADC sources as well. We conclude that unless there exists some means of coronal heating other than X-rays, the true source luminosity is likely much higher, and we observe obscuration in analogy to the extragalactic Seyfert 2 sources. We discuss possible consequences and relate cold, lukewarm, warm, and hot absorbers to dynamic accretion scenarios.

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“…Partial covering models have been frequently applied to the X-ray spectra of AGNs and NLS1 galaxies in particular (e.g., Grupe et al 2004bGrupe et al , 2004cGallo et al 2004;Pounds et al 2004;Tanaka et al 2005) and also to Galactic X-ray binaries (e.g., Brandt et al 1996;Ding et al 2006). However, origin and confinement of the required dense blobs of gas in AGN partial coverers are not well understood (e.g., Kuncic et al 1997).…”

Section: Discussionmentioning

confidence: 99%

XMM‐NewtonObservations of the Narrow‐Line Seyfert 1 Galaxy Mrk 335 in a Historical Low X‐Ray Flux State

Grupe

Komossa

Gallo

et al. 2008

ApJ

138

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We report the discovery of strong soft X-ray emission lines and a hard continuum above 2 keV in the narrow-line Seyfert 1 galaxy Mrk 335 during an extremely low X-ray flux state. Mrk 335 was observed for 22 ks by XMM-Newton in 2007 July as a Target of Opportunity to examine it in its X-ray low flux state, which was discovered with Swift. Long-term light curves suggest that this is the lowest flux state this AGN has ever been seen in. However, Mrk 335 is still sufficiently bright that its X-ray properties can be studied in detail. The X-ray continuum spectrum is very complex and requires several components to model. Statistically, partial covering and blurred reflection models work well. We confirm the presence of a strong narrow Fe line at 6.4 keV. High-resolution spectroscopy with the XMMNewton RGS reveals strong, soft X-ray emission lines not detected in previous, higher signal-to-noise ratio, XMMNewton observations, such as highly ionized Fe lines, O vii, and Ne ix and Mg xi lines. The optical /UV fluxes are similar to those previously measured with Swift. Optical spectroscopy taken in 2007 September does not show any changes to optical spectra obtained 8 years earlier.

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Partial Covering during Long-Term Dips in Circinus X-1

Cited by 16 publications

References 32 publications

Linking jet emission and X-ray properties in the peculiar neutron star X-ray binary Circinus X-1

Linking jet emission and X-ray properties in the peculiar neutron star X-ray binary Circinus X-1

The Variable Warm Absorber in Circinus X‐1

XMM‐NewtonObservations of the Narrow‐Line Seyfert 1 Galaxy Mrk 335 in a Historical Low X‐Ray Flux State

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