On the hard X-ray variability of Centaurus A

Jourdain, E.; Bassani, L.; Roques, J. P.; Mandrou, P.; Ballet, J.; Claret, A.; Laurent, P.; Lebrun, F.; Finogenov, A.; Churazov, E.; Gilfanov, M.; Sunyaev, R.; Dyachkov, A.; Khavenson, N.; Sukhanov, K. G.; Kremnev, R. S.

doi:10.1086/172945

Cited by 28 publications

(42 citation statements)

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“…Centaurus A is known to be a highly variable object on both long and short time scales (Jourdain et al 1993). Within 10 months, the hard X-ray flux of Centaurus A has changed by a factor of ∼2 in INTEGRAL data.…”

Section: Discussion On Individual Sourcesmentioning

confidence: 99%

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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Section: Discussion On Individual Sourcesmentioning

confidence: 99%

INTEGRAL observations of six AGN in the Galactic Plane

Soldi

Beckmann

Bassani

et al. 2005

A&A

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“…At X-ray wavelengths, Cen A is known to be highly variable on time scales of years, months, and days (Jourdain et al 1993;Baity et al 1981). This variability can be split in two main components (Jourdain et al 1993): (1) long-term trends which last for years and define the state of the source and (2) short-term flares of a few days which are superposed on the long-term component.…”

Section: Timing Analysismentioning

confidence: 99%

RXTE monitoring of Centaurus A

Benlloch

Rothschild

Wilms

et al. 2001

A&A

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Abstract.We report on the analysis from ∼110 ks of X-ray observations of Centaurus A carried out with the Proportional Counter Array (PCA) and the High Energy X-ray Timing Experiment (HEXTE) instruments on Rossi X-ray Timing Explorer (RXTE) during three monitoring campaigns over the last 4 years (10 ks in 1996, 74 ks in 1998, and 25 ks in 2000). The joint PCA/HEXTE X-ray spectrum can be well described by a heavily absorbed power law with photon index 1.8 and a narrow iron line due to fluorescence of cold matter. The measured column depth decreased by about 30% between 1996 and 2000, while the detected 2-10 keV continuum flux remained constant between 1996 and 1998, but increased by 60% in 2000. Since in all three observations the iron line flux did not vary, a corresponding decrease in equivalent width was noted. No appreciable evidence for a reflection continuum in the spectrum was detected. We present the interpretation of the iron line strength through Monte Carlo computations of various geometries. No significant temporal variability was found in Cen A at time scales from days to tens of minutes.

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“…The Cen A was found in the relatively high state only during two observations in 1991 (observations 308 and 311 in Table 3). These two observations were separated by 4 days and the flux in the latter observation was significantly lower than in the first one (Jourdain et al,1993). If the fast decrease of the flux between these two observations characterizes also the rise time, than it is possible that the source remained in the low state during whole period of SIGMA observations in 1990-1993 and two observations in 1991 July occasionally happened during relatively short flare of the source.…”

Section: Cen Amentioning

confidence: 95%

“…The results of AGNs observations with GRANAT during first years of the mission are presented in a number of papers by Apalkov et al, 1992(ART-P, observations in 1990, 3C273, NGC 4151, Cen A); Ballet et al, 1991Ballet et al, , 1992a and ART-P, 1990-1992,3C273, NGC 4151, Cen A); Jourdain et al, 1992(SIGMA, 1990, NGC4151); Bassani et al, 1992(SIGMA, 1990; Jourdain et al, 1993(SIGMA, 1990, Cen A); Lebrun et al, 1992(SIGMA, 1990 and NGC4388); Bassani et al, 1993(SIGMA, 1992, 3C273, NGC4151, Cen A), Finoguenov et al, 1993(ART-P & SIGMA, 1990). We will concentrate below on the data of observations in the hard X-ray / soft Gamma-ray band obtained by GRAN AT/SIGMA.…”

Section: Introductionmentioning

confidence: 99%

Review of GRANAT Observations of AGNs

Churazov

Gilfanov

Finoguenov

et al. 1994

Symp. - Int. Astron. Union

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Abstract. Brief review of AGNs observations in the X-ray / soft gamma-ray bands with the orbital observatory GRANAT is presented.For three well known bright objects (3C273, NGC4151 and Cen A) broad band (3 keVfew hundreds keV) spectra have been obtained. Imaging capabilities allowed accurate (several arcminutes) identification of these objects with sources of hard X-rays.The spectrum of NGC4151 above « 50 keV was found to be much steeper than that in most of the previous observations, while in standard X-ray band the spectrum agrees with observed previously. The comparison of the observed spectra with that of the X-Ray Background (XRB) indicates that sources similar to NGC4151 could reproduce the shape of XRB spectrum in 3-60 keV band.Cen A was observed in the very low state during most of observations in 1990-1993, except for two observations in 1991. The variability of the hard X-ray flux has been detected on the time scales of several days.

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On the hard X-ray variability of Centaurus A

Cited by 28 publications

References 0 publications

INTEGRAL observations of six AGN in the Galactic Plane

INTEGRAL observations of six AGN in the Galactic Plane

RXTE monitoring of Centaurus A

Review of GRANAT Observations of AGNs

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