* Astronomy

Blobrana · L

RE: NGC 5548

Blobrana · L

Title: Swift monitoring of NGC 5548: X-ray reprocessing and short term UV/optical variability
Author: I. M. McHardy (1), D. T. Cameron (1), T. Dwelly (2 and 1), S. Connolly (1), P. Lira (3), D. Emmanoulopoulos (1), J. Gelbord (4), E. Breedt (5), P. Arevalo (6 and 7), P. Uttley (8) ((1) University of Southampton,(2) Max-Planck-Institut fur extraterrestrische Physik, (3) Universidad de Chile, (4) Spectral Sciences Inc, (5) University of Warwick (6) Pontifcia Universidad Catolica de Chile (7) Universidad de Valparaiso (8) Astronomical Institute `Anton Pannekoek')

Lags measured from correlated X-ray/UV/optical monitoring of AGN allow us to determine whether UV/optical variability is driven by reprocessing of X-rays or X-ray variability is driven by UV/optical seed photon variations. We present the results of the largest study to date of the relationship between the X-ray, UV and optical variability in an AGN with 554 observations, over a 750d period, of the Seyfert 1 galaxy NGC 5548 with Swift. There is a good overall correlation between the X-ray and UV/optical bands, particularly on short timescales (tens of days). These bands lag the X-ray band with lags which are proportional to wavelength to the power 1.23+/-0.31. This power is very close to the power (4/3) expected if short timescale UV/optical variability is driven by reprocessing of X-rays by a surrounding accretion disc.
The observed lags, however, are longer than expected from a standard Shakura-Sunyaev accretion disc with X-ray heating, given the currently accepted black hole mass and accretion rate values, but can be explained with a slightly larger mass and accretion rate, and a generally hotter disc.
Some long term UV/optical variations are not paralleled exactly in the X-rays, suggesting an additional component to the UV/optical variability arising perhaps from accretion rate perturbations propagating inwards through the disc.

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Blobrana · L

Title: Accretion disk wind as explanation for the broad-line region structure in NGC 5548
Authors: W. Kollatschny, M. Zetzl

Supermassive black holes in the centers of active galactic nuclei (AGN) are surrounded by broad-line regions (BLRs). The broad emission lines seen in the AGN spectra are emitted in this spatially unresolved region. We intend to obtain information on the structure and geometry of this BLR based on observed line profiles. We modelled the rotational and turbulent velocities in the line-emitting region on the basis of the line-width FWHM and line dispersion sigma_line of the variable broad emission lines in NGC5548. Based on these velocities we estimated the height of the line-emitting regions above the midplane in the context of their distances from the center. The broad emission lines originate at distances of 2 to 27 light days from the center. Higher ionised lines originate in the inner region (lesser equal 13 light days) in specific filamentary structures 1 to 14 light days above the midplane. In contrast, the Hbeta line is emitted in an outer (6 - 26 light days), more flattened configuration at heights of 0.7 to 4 light days only above the midplane. The derived geometry of the line-emitting region in NGC5548 is consistent with an outflowing wind launched from an accretion disk.

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Blobrana · L

Title: Suzaku Monitoring of the Iron K Emission Line in the Type 1 AGN NGC 5548
Authors: Yuan Liu, Martin Elvis, Ian M. McHardy, Dirk Grupe, Belinda J. Wilkes, James Reeves, Nancy Brickhouse, Yair Krongold, Smita Mathur, Takeo Minezaki, Fabrizio Nicastro, Yuzuru Yoshii, Shuang Nan Zhang

We present 7 sequential weekly observations of NGC 5548 conducted in 2007 with the Suzaku X-ray Imaging Spectrometer (XIS) in the 0.2-12 keV band and Hard X-ray Detector (HXD) in 10-600 keV band. The iron K\alpha line is well detected in all seven observations and K\beta line is also detected in four observations. In this paper, we investigate the origin of the Fe K lines using both the width of the line and the reverberation mapping method.
With the co-added XIS and HXD spectra, we identify Fe K\alpha and K\beta line at 6.396_{-0.007}^{+0.009} keV and 7.08$_{-0.05}^{+0.05} keV, respectively. The width of line obtained from the co-added spectra is 38_{-18}^{+16} eV (FWHM=4200_{-2000}^{+1800} km/s) which corresponds to a radius of 20_{-10}^{+50} light days, for the virial production of 1.220 x 10^7 solar masses in NCG 5548.
To quantitatively investigate the origin of the narrow Fe line by the reverberation mapping method, we compare the observed light curves of Fe K$\alpha$ line with the predicted ones, which are obtained by convolving the continuum light curve with the transfer functions in a thin shell and an inclined disk. The best-fit result is given by the disk case with i=30° which is better than a fit to a constant flux of the Fe K line at the 92.7% level (F-test). We find that the emitting radius obtained from the light curve is 25-37 light days, which is consistent with the radius derived from the Fe K line width. Combining the results of the line width and variation, the most likely site for the origin of the narrow iron lines is 20-40 light days away from the central engine, though other possibilities are not completely ruled out.

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Blobrana · L

Title: Mass Outflow in the Seyfert 1 Galaxy NGC 5548
Authors: D.M. Crenshaw, S.B. Kraemer, H.R. Schmitt, J.S. Kaastra, N. Arav, J.R. Gabel, K.T. Korista

We present a study of the intrinsic UV absorption and emission lines in an historically low-state spectrum of the Seyfert 1 galaxy NGC 5548, which we obtained in 2004 February at high spatial and spectral resolution with the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope. We isolate a component of emission with a width of 680 km/s (FWHM) that arises from an "intermediate line region" (ILR), similar to the one we discovered in NGC 4151, at a distance of ~1 pc from the central continuum source. From a detailed analysis of the five intrinsic absorption components in NGC 5548 and their behaviour over a span of 8 years, we present evidence that most of the UV absorbers only partially cover the ILR and do not cover an extended region of UV continuum emission, most likely from hot stars in the circumnuclear region. We also find that four of the UV absorbers are at much greater distances (>70 pc) than the ILR, and none have sufficient N V or C IV column densities to be the ILR in absorption. At least a portion of the UV absorption component 3, at a radial velocity of -530 km/s, is likely responsible for most of the X-ray absorption, at a distance < 7 pc from the central source. The fact that we see the ILR in absorption in NGC 4151 and not in NGC 5548 suggests that the ILR is located at a relatively large polar angle (~45 degrees) with respect to the narrow-line region outflow axis.

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