arXiv subjects

Z. Tsvetanov

Publications and source records attributed to Z. Tsvetanov.

22 records · Page 2Linked to original sources

arXiv1997

Are Seyfert Narrow Line Regions Powered by Radio Jets?

We argue that the narrow line regions of Seyfert galaxies are powered by the transport of energy and momentum by the radio-emitting jets and consequently that the ratio of the radio power to jet energy flux is much smaller than is usually assumed for radio galaxies. This can be partially attributed to the smaller ages ($\sim 10^6 yrs$) of Seyferts compared to radio galaxies but one also requires that either the magnetic energy density is more than an order of magnitude below the equipartition value, or more likely, that the internal energy densities of Seyfert jets are dominated by thermal plasma. If Seyfert jets are initially dominated by relativistic plasma, then an analysis of the data on jets in five Seyfert galaxies shows that all but one of these would have mildly relativistic jet velocities near 100 pc in order to power the respective narrow-line regions. However, observations of jet-cloud interactions in the NLR provide additional information on jet velocities and composition via the momentum budget. Our analysis of a jet-cloud interaction in NGC 1068, implies a shocked jet pressure much larger than the minimum pressure of the radio knot, a velocity $\sim 0.06 c$ and a jet temperature $\sim 10^9 K$ implying mildly relativistic electrons but thermal protons. The jet mass flux at this point $\sim 0.5 M_\odot yr^{-1}$, is an order of magnitude higher than the mass accretion rate into the black hole, strongly indicating entrainment. The initial jet mass flux $\sim 0.02 M_\odot yr^{-1}$, comparable to the mass accretion rate and is consistent with the densities inferred for accretion disc coronae from high energy observations, together with an initially mildly relativistic velocity and an initial jet radius of order 10 gravitational radii.

astro-ph↗

arXiv1996

HUT Observations of the Lyman Limit in AGN: Implications for Unified Models

We observed a total of 13 low-redshift AGN with the Hopkins Ultraviolet Telescope (HUT) during the course of the Astro-1 and Astro-2 missions. Of these, 4 show intrinsic Lyman limit absorption---NGC 1068, NGC 4151, NGC 3516 and NGC 3227. All galaxies with optically thick Lyman limits have extended narrow-line regions with bi-polar morphologies. All AGN with no absorption are Seyfert 1's with compact NLR's. These observations support geometrical shadowing as the means for collimating the ionizing radiation in unified models of AGN, most likely in a photoionized atmosphere above the obscuring torus.

astro-ph↗

arXiv1996

Far-Ultraviolet Observations of NGC 3516 using the Hopkins Ultraviolet Telescope

We observed the Seyfert 1 galaxy NGC 3516 twice during the flight of Astro-2 using the Hopkins Ultraviolet Telescope in March 1995. Simultaneous X-ray observations were performed with ASCA. Our far-ultraviolet spectra cover the spectral range 820-1840 A with a resolution of 2-4 A. No significant variations were found between the two observations. The total spectrum shows a red continuum, $f_ν\sim ν^{-1.89}$, with an observed flux of $\rm 2.2 \times 10^{-14}~erg~cm^{-2}~s^{-1}~Å^{-1}$ at 1450 A, slightly above the historical mean. Intrinsic absorption in Lyman $β$ is visible as well as absorption from O~vi 1032,1038, N~v 1239,1243, Si~iv 1394,1403, and C~iv 1548,1551. The UV absorption lines are far weaker than is usual for NGC~3516, and also lie closer to the emission line redshift rather than showing the blueshift typical of these lines when they are strong. The neutral hydrogen absorption, however, is blueshifted by $400~\rm km~s^{-1}$ relative to the systemic velocity, and it is opaque at the Lyman limit. The sharpness of the cutoff indicates a low effective Doppler parameter, $b < \rm 20~km~s^{-1}$. For $b = \rm 10~km~s^{-1}$ the derived intrinsic column is $\rm 3.5 \times 10^{17}~cm^{-2}$. As in NGC~4151, a single warm absorber cannot produce the strong absorption visible over the wide range of observed ionization states. Matching both the UV and X-ray absorption simultaneously requires absorbers spanning a range of $10^3$ in both ionization parameter and column density.

astro-ph↗

arXiv1996

ASCA Observations of the Composite Warm Absorber in NGC 3516

We obtained X-ray spectra of the Seyfert 1 galaxy NGC~3516 in March 1995 using ASCA. Simultaneous far-UV observations were obtained with HUT on the Astro-2 shuttle mission. The ASCA spectrum shows a lightly absorbed power law of energy index 0.78. The low energy absorbing column is significantly less than previously seen. Prominent O~vii and O~viii absorption edges are visible, but, consistent with the much lower total absorbing column, no Fe K absorption edge is detectable. A weak, narrow Fe~K$α$ emission line from cold material is present as well as a broad Fe~K$α$ line. These features are similar to those reported in other Seyfert 1 galaxies. A single warm absorber model provides only an imperfect description of the low energy absorption. In addition to a highly ionized absorber with ionization parameter $U = 1.66$ and a total column density of $1.4 \times 10^{22}~\rm cm^{-2}$, adding a lower ionization absorber with $U = 0.32$ and a total column of $6.9 \times 10^{21}~\rm cm^{-2}$ significantly improves the fit. The contribution of resonant line scattering to our warm absorber models limits the Doppler parameter to $< 160~\rm km~s^{-1}$ at 90\% confidence. Turbulence at the sound speed of the photoionized gas provides the best fit. None of the warm absorber models fit to the X-ray spectrum can match the observed equivalent widths of all the UV absorption lines. Accounting for the X-ray and UV absorption simultaneously requires an absorbing region with a broad range of ionization parameters and column densities.

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