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Register a new userThe ASCA X-ray spectrum of the powerful radio galaxy 3C109
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We report the results from an ASCA X-ray observation of the powerful Broad Line Radio Galaxy, 3C109. The ASCA spectra confirm our earlier ROSAT detection of intrinsic X-ray absorption associated with the source. The absorbing material obscures a central engine of quasar-like luminosity. The luminosity is variable, having dropped by a factor of two since the ROSAT observations 4 years before. The ASCA data also provide evidence for a broad iron emission line from the source, with an intrinsic FWHM of ~ 120,000 km/s. Interpreting the line as fluorescent emission from the inner parts of an accretion disk, we can constrain the inclination of the disk to be $> 35$ degree, and the inner radius of the disk to be $< 70$ Schwarzschild radii. Our results support unified schemes for active galaxies, and demonstrate a remarkable similarity between the X-ray properties of this powerful radio source, and those of lower luminosity, Seyfert 1 galaxies.
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shortened) Results obtained from 9 X-ray observations of 3C 273 performed by ASCA are presented (for a total exposure time of about 160 000 s). The analysis and interpretation of the results is complicated by the fact that 4 of these observations were used for on-board calibration of the CCDs spectral response. The present analysis shows that, in agreement with official recommendations, a conservative systematic error (at low energies) of about 2-3 x 10**20cm-2 must be assumed when analyzing ASCA SIS data. A soft-excess, with variable flux and/or shape, has been clearly detected as well as flux and spectral variability. An anti-correlation is found between the spectral index and the flux in the 2-10 keV energy range. Fitting the data with the latest available calibration matrices, we also detect an emission line at ~5.4-5.7 keV (~6.3-6.6 keV in the quasar frame) in (only) the two observations with lowest fluxes where it is weak (EW ~ 20-30 eV), narrow and consistent with being produced by Fe K emission from neutral matter. Overall, the observations are qualitatively consistent with a variable, non-thermal X-ray continuum emission, i.e., a power law with Gamma~1.6 (possibly produced in the innermost regions of the radio-optical jet), plus underlying ``Seyfert-like features, i.e., a soft-excess and Fe K line emission due to a reflection component. When the continuum (jet) emission is in a low state, the spectral features produced by the Seyfert-like spectrum (soft-excess, iron line and possibly a steep power law plus reflection continuum) are more easily seen.
We report X-ray imaging of the powerful FR-II radio galaxy 3C353 using the Chandra X-ray Observatory. 3C353s two 4-wide and 2-long jets allow us to study in detail the internal structure of the large-scale relativistic outflows at both radio and X-ray photon energies with the sub-arcsecond spatial resolution. In a 90 ks Chandra observation, we have detected X-ray emission from most radio structures in 3C353, including the nucleus, the jet and the counterjet, the terminal jet regions (hotspots), and one radio lobe. We show that the detection of the X-ray emission associated with the radio knots and counterknots puts several crucial constraints on the X-ray emission mechanisms in powerful large-scale jets of quasars and FR-II sources. In particular, we show that this detection is inconsistent with the inverse-Compton model proposed in the literature, and instead implies a synchrotron origin of the X-ray jet photons. We also find that the width of the X-ray counterjet is possibly narrower than that measured in radio bands, that the radio-to-X-ray flux ratio decreases systematically downstream along the jets, and that there are substantial (kpc-scale) offsets between the positions of the X-ray and radio intensity maxima within each knot, whose magnitudes increase away from the nucleus. We discuss all these findings in the wider context of the physics of extragalactic jets, proposing some particular though not definitive solutions or interpretations for each problem.
We report on the X-ray observation of the radio selected supernova SN1979C carried out with ASCA in December 1997. The supernova of type II$_{L}$ was first observed in the optical and occurred in the weakly barred, almost face on spiral galaxy NGC 4321 (M100) which is at a distance of 17.1 Mpc, and contains at least three other supernovae discovered in this century. No point source was detected at the radio position of SN1979C in a 3 diameter half power response circle in a 27.3 ks SIS exposure. The background and galaxy subtracted SN signal had a 3$sigma$ upper limit to the count rate of 1.2$times 10^{-3}$ cps in the full ASCA SIS band (0.4-10.0 keV). These measurements give the first ever x-ray flux limit of a Type II$_{L}$ SN in the higher energy band ($geq$ 2 keV) which is an important diagnostic of the {it outgoing} shock wave ploughing through the circumstellar medium.
We present the results of the analysis of an archival 15 ks XMM-Newton observation of the nearby (z=0.057) radio-loud source 3C445, optically classified as a Broad-Line Radio Galaxy. While the RGS data are of insufficient quality to allow a meaningful analysis, the EPIC data show a remarkable X-ray spectrum. The 2-10 keV continuum is described by a heavily absorbed (Nh~ 1e22 - 1e23 cm-2) power law with photon index Gamma ~1.4, and strong (R~2) cold reflection. A narrow, unresolved Fe Kalpha emission line is detected, confirming previous findings, with EW 120eV. A soft excess is present below 2 keV over the extrapolation of the hard X-ray power law, which we model with a power law with the same photon index as the hard power law, absorbed by a column density Nh=6e20 cm-2 in excess to Galactic. A host of emission lines are present below 2 keV, confirming previous indications from ASCA, due to H- and He-like O, Mg, and Si. We attribute the origin of the lines to a photoionized gas, with properties very similar to radio-quiet obscured AGN. Two different ionized media, or a single stratified medium, are required to fit the soft X-ray data satisfactorily. The similarity of the X-ray spectrum of 3C445 to Seyferts underscores that the central engines of radio-loud and radio-quiet AGN similarly host both cold and warm gas.
We present an analysis of the rosat and asca spectra of 21 broad line AGN (QSOs) with $zsim 1$ detected in the 2-10 keV band with the asca gis. The summed spectrum in the asca band is well described by a power-law with $Gamma=1.56pm0.18$, flatter that the average spectral index of bright QSOs and consistent with the spectrum of the X-ray background in this band. The flat spectrum in the asca band could be explained by only a moderate absorption ($sim 10^{22} rm cm^{-2}$) assuming the typical AGN spectrum ie a power-law with $Gamma$=1.9. This could in principle suggest that some of the highly obscured AGN, required by most X-ray background synthesis models, may be associated with normal blue QSOs rather than narrow-line AGN. However, the combined 0.5-8 keV asca-rosat spectrum is well fit by a power-law of $Gamma=1.7pm0.2$ with a spectral upturn at soft energies. It has been pointed out that such an upturn may be an artefact of uncertainties in the calibration of the ROSAT or ASCA detectors. Nevertheless if real, it could imply that the above absorption model suggested by the asca data alone is ruled out. Then a large fraction of QSOs could have ``concave spectra ie they gradually steepen towards softer energies. This result is in agreement with the bepposax hardness ratio analysis of $sim$ 100 hard X-ray selected sources.
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