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Register a new userA Broad Fe-Kalpha Emission Line in the X-Ray Spectrum of the Quasar 3C 273
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T. Yaqoob Lhea
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The Fe-K line, an important physical diagnostic in the X-ray spectra of AGN, has been notoriously difficult to measure in the high-luminosity, radio-loud quasar 3C 273 (z=0.158). On the few occasions that it has been detected its intrinsic width has been thought to be narrow (FWHM < 10,000 km/s) with an equivalent width (EW) of a few tens of eV.This was consistent with the general trend that as one goes from low to high luminosity AGNs the Fe-K line goes from being strong (EW ~200-300 eV) and broad (FWHM ~ 100,000 km/s) to being weak and narrow, or absent altogether. Here we present the results of new ASCA and RXTE observations, together with archival ASCA data, and show for the first time that the Fe-K line in 3C 273 is as broad as that seen in Seyfert 1. The line is resolved in two of the observations, with a mean Gaussian width of 0.8 +/- 0.3 keV, or FWHM of 0.3 +/- 0.1c. The smallest and largest EW measured is 43 +/- 34 eV, and 133 (+52,-53) eV respectively (quasar frame). The Compton-reflection continuum is less than 10% of that expected from a centrally illuminated semi-infinite, face-on, Compton-thick disk, confirming previous studies that Compton reflection is negligible in 3C 273. The largest values of the Fe-K line EW are under-predicted if the line originates in the disk, unless a time lag longer than several days between line and continuum and/or an over-abundance of Fe is invoked. We cannot unambiguously constrain the disk inclination angle. About 60 deg is preferred for a cold disk, while a face-on disk is allowed if the ionization state of Fe is H-like.
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We present results from four recent Chandra monitoring observations of the jet in 3C 273 using the ACIS detector, obtained between November 2003 and July 2004. We find that the X-ray emission comes in two components: unresolved knots that are smaller than the corresponding optically emitting knots and a broad channel that is about the same width as the optical interknot region. We compute the jet speed under the assumption that the X-ray emission is due to inverse Compton scattering of the cosmic microwave background, finding that the dimming of the jet X-ray emission to the jet termination relative to the radio emission may be due to bulk deceleration.
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 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.
In 3C 273, ultraviolet flux and X-ray flux measured by BATSE are not well correlated, contrarily to predictions of several models, unless the X-ray flux lags the UV emission by 1.75 yr. The absence of observed correlation at small lag cannot be due to spectral variability. A Comptonizing corona model is however compatible with all UV and X-ray observations covering the BATSE period.
We have analysed the first 15 months of Fermi/LAT data of the radio loud quasar 3C 273. Intense gamma-ray activity has been detected, showing an average flux of F(> 100 MeV) = 1.4e-6 ph/cm^2/s, with a peak at F(> 100 MeV) = 5.6e-6 ph/cm^2/s detected during a flare in September 2009. Together with the brightening of the source, a possible hardening of the gamma-ray spectrum is observed, pointing to a shift of the inverse Compton peak toward higher energies than the 1-10 MeV range in which 3C 273 inverse Compton emission is typically observed to peak. During the 15 months of observations the photon index is measured to vary between 2.4 and 3.3, with an average value of 2.78 +/- 0.03. When compared to the observations at other wavelengths, the gamma-rays show the largest flux variations and we discuss the possibility that two different components are responsible for the inverse Compton hump emission below and above the MeV peak.
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