Observation of Centaurus A by the<i>Rossi X‐Ray Timing Explorer</i>

Rothschild, R. E.; Band, D. L.; Blanco, P. R.; Gruber, D. E.; Heindl, W. A.; MacDonald, D.; Marsden, D.; Jahoda, K.; Pierce, Donna M.; Madejski, G. M.; Elvis, M.; Schwartz, D. A.; Remillard, Ronald A.; Zdziarski, A. A.; Done, Chris; Svensson, Roger

doi:10.1086/306618

Cited by 18 publications

(26 citation statements)

References 30 publications

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“…This is consistent with emission from material at a large distance from the site of the hard X-ray emission. The lack of change in the flux of the Cen A iron line over 20 years despite significant changes in the strength of the observed hard X-ray continuum (Rothschild et al 1999), supports this suggestion that the absorbing/fluorescing material is at least several parsecs from the central engine or insensitive to contunuum variations (e.g. Miniutti et al 2003).…”

Section: Previous Observationssupporting

confidence: 54%

INTEGRAL and RXTE Observations of Centaurus A

Rothschild¹,

Wilms²,

Tomsick³

et al. 2006

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INTEGRAL and RXTE performed three simultaneous observations of the nearby radio galaxy Centaurus A in March, 2004 January, and 2004 February with the goals of investigating the geometry and emission processes via the spectral/temporal variability of the X-ray/low energy gamma ray flux, and intercalibration of the INTEGRAL instruments with respect to those on RXTE. Cen A was detected by both sets of instruments from 3-240 keV. When combined with earlier archival RXTE results, we find the power law continuum flux and the line-of-sight column depth varied independently by 60% between 2000 January and 2003 March. Including the three archival RXTE observations, the iron line flux was essentially unchanging, and from this we conclude that the iron line emitting material is distant from the site of the continuum emission, and that the origin of the iron line flux is still an open question. Taking X-ray spectral measurements from satellite missions since 1970 into account, we discover a

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Section: Previous Observationssupporting

confidence: 54%

INTEGRAL and RXTE Observations of Centaurus A

Rothschild¹,

Wilms²,

Tomsick³

et al. 2006

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“…INTEGRAL observations confirm the lack of a Compton reflection, as adding this component does not improve the fits and results in a reflection fraction <0.1. Only an upper limit can be derived from JEM-X data for the fluorescence iron line at 6.4 keV, with a flux an order of magnitude above the values found in the literature (Grandi et al 2003;Rothschild et al 1999).…”

Section: Discussion On Individual Sourcesmentioning

confidence: 79%

INTEGRAL observations of six AGN in the Galactic Plane

Soldi

Beckmann

Bassani

et al. 2005

A&A

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We present results on approximately one year of INTEGRAL observations of six AGN detected during the regular scans of the Galactic Plane. The sample is composed by five Seyfert 2 objects (MCG -05-23-16, NGC 4945, the Circinus galaxy, NGC 6300, ESO 103-G35) and the radio galaxy Centaurus A. The continuum emission of each of these sources is well represented by a highly absorbed (N H > 10 22 cm −2 ) power law, with average spectral index Γ = 1.9 ± 0.3. A high energy exponential cut-off at E c ∼ 50 keV is required to fit the spectrum of the Circinus galaxy, whereas a lower limit of 130 keV has been found for NGC 4945 and no cut-off has been detected for NGC 6300 in the energy range covered by these INTEGRAL data. The flux of Centaurus A was found to vary by a factor of ∼2 in 10 months, showing a spectral change between the high and low state, which can be modelled equally well by a change in the absorption (N H from 17 to 33 × 10 22 cm −2 ) or by the presence of a cut-off at > ∼ 120 keV in the low state spectrum. A comparison with recently reprocessed BeppoSAX/PDS data shows a general agreement with INTEGRAL results. The high energy cut-off in the hard X-ray spectra appears to be a common but not universal characteristic of Seyfert 2 and to span a wide range of energies.

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“…It is generally modeled with a power law heavily absorbed by dense and probably stratified matter (N H $ 10 À23 cm À2 ) and by an iron line (Mushotzky et al 1978;Wang et al 1986;Morini et al 1989;Miyazaki et al 1996;Turner et al 1997;Sugizaki et al 1997). In contrast to Seyfert galaxies, the iron line of Cen A is not associated with a strong Compton reflection (Miyazaki et al 1996;Woźniak et al 1998;Rothschild et al 1999), as one would expect if the line were produced by cold and optically thick gas. This convinced many authors that the Fe feature is produced by the cold, dense, but optically thin, gas that is also responsible for the observed photoelectric absorption (N H ) surrounding the X-ray source (Miyazaki et al 1996;Woźniak et al 1998;Miyazaki et al 1996;Benlloch et al 2001).…”

Section: Introductionmentioning

confidence: 99%

BeppoSAXObservations of Centaurus A: The Hard Continuum and the Iron‐Line Feature

Grandi

Fiocchi²,

Perola

et al. 2003

ApJ

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The radio galaxy Centaurus A was observed by the BeppoSAX satellite five times from 1997 to 2000. From 1999 July 6 to 1999 August 17, the source was also simultaneously observed by COMPTEL on board the Compton Gamma Ray Observatory. Centaurus A has a complex spectrum with multiple extended components and a strongly absorbed (N H $ 10 23 cm À2 ) nucleus well fitted by a power law (À $ 1:8) that bends at high energies. When the BeppoSAX and COMPTEL observations are combined together, an exponential cutoff with an e-folding energy of $600 keV gives an adequate description of the spectral steepening. A complex feature in emission at 6-7 keV is resolved into two Fe K components, one narrow cold line and an ionized line centered at 6.8 keV. Significant variations have been observed in the iron feature, with the less prominent ionized line seemingly being the only one responsible for them: its variations do not appear to correlate with the strength of the continuum. The high-energy cutoff and the Fe feature suggest the presence of an accretion flow in the Centaurus A nucleus. However, the absence of a significant reflection and the narrowness of the cold line, as well as the lack of correlation between the continuum and 6.8 keV line variations, disfavor a standard cold/ionized thin disk (at least in the inner regions). A more plausible configuration might be a hot, thick, optically thin accretion flow surrounded by material with different opacities. Finally, we note that the high-energy break observed by BeppoSAX and COMPTEL could be also reasonably explained by inverse Compton radiation from a jet. If this is the case, a structured jet with outer slow layers surrounding a beamed inner region is necessary to explain the strong Fe feature observed by BeppoSAX.

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Observation of Centaurus A by theRossi X‐Ray Timing Explorer

Cited by 18 publications

References 30 publications

INTEGRAL and RXTE Observations of Centaurus A

INTEGRAL and RXTE Observations of Centaurus A

INTEGRAL observations of six AGN in the Galactic Plane

BeppoSAXObservations of Centaurus A: The Hard Continuum and the Iron‐Line Feature

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