Characterization of monoclonal and polyclonal antibodies to bovine enteric coronavirus: Establishment of an efficient ELISA for antigen detection in feces

Monoclonal antibodies to bovine enteric coronavirus (BEC) were produced. Additionally, polyclonal antibodies were made in rabbits and guinea pigs and extracted from the yolk of immunized hens. The antibodies were characterized by neutralization test, hemagglutination inhibition test, enzyme-linked immunosorbent assay (ELISA) and immunoblotting. Neutralizing antibody titers of polyclonal antisera ranged from 1:1280 to 1:40 000. Only one out of 908 hybridoma colonies tested secreted antibodies with neutralizing activity. By ELISA, polyclonal sera exhibited high background reactions that could be significantly reduced by treatment with kaolin in the case of rabbit sera. Attempts to establish an ELISA for BEC antigen detection based on polyclonal sera failed due to low sensitivity and specificity. Optimal results were achieved when a mixture of two monoclonal antibodies was coated onto microplates for antigen capture, while rabbit hyperimmune serum served as detecting antibodies in an indirect assay. The combination of the two monoclonal antibodies did not increase sensitivity synergistically, but in a compensatory fashion, probably because of epitope differences between BEC field strain

On the Intermediate Line Region in AGNs

In this paper we explore the intermediate line region (ILR) by using the photoionisation simulations of the gas clouds present at different radial distances from the center, corresponding to the locations from BLR out to NLR in four types of AGNs. We let for the presence of dust whenever conditions allow for dust existence. All spectral shapes are taken from the recent multi-wavelength campaigns. The cloud density decreases with distance as a power law. We found that the slope of the power law density profile does not affect the line emissivity radial profiles of major emission lines: H${\beta}$, He~II, Mg~II, C~III] ~and [O~III]. When the density of the cloud at the sublimation radius is as high as 10$^{11.5}$ cm$^{-3}$, the ILR should clearly be seen in the observations independently of the shape of the illuminating radiation. Moreover, our result is valid for low ionization nuclear emission regions of active galaxies.Comment: 8 pages, 2 figures, Accepted for publication in the Journal Frontiers in Astronomy and Space Science

Vertical Structure of Accretion Discs with Hot Coronae in AGN

We study vertical structure of radiation pressure dominated disc with a hot corona. We include all the relevant processes like bound--free opacity and convection. We show that the presence of the corona modifies considerably the density and the opacity of the disc surface layers which are important from the point of view of spectrum formation. The surface of the disc with a corona is much denser and less ionized than the surface of a bare disc. Such a disc is likely to produce a neutral reflection and a local spectrum close to a black body. This effect will help to reconcile the predictions of accretion disc models with the observational data since a neutral reflection and a lack of Lyman edge are generally seen in AGN.Comment: 10 pages, 9 figures, submitted to MNRA

The existence of warm and optically thick dissipative coronae above accretion disks

In the past years, several observations of AGN and X-ray binaries have suggested the existence of a warm T around 0.5-1 keV and optically thick, \tau ~ 10-20, corona covering the inner parts of the accretion disk. These properties are directly derived from spectral fitting in UV to soft-X-rays using Comptonization models. However, whether such a medium can be both in radiative and hydrostatic equilibrium with an accretion disk is still uncertain. We investigate the properties of such warm, optically thick coronae and put constraints on their existence. We solve the radiative transfer equation for grey atmosphere analytically in a pure scattering medium, including local dissipation as an additional heating term in the warm corona. The temperature profile of the warm corona is calculated assuming it is cooled by Compton scattering, with the underlying dissipative disk providing photons to the corona. Our analytic calculations show that a dissipative thick, (\tau_{cor} ~ 10-12) corona on the top of a standard accretion disk can reach temperatures of the order of 0.5-1 keV in its upper layers provided that the disk is passive. But, in absence of strong magnetic fields, the requirement of a Compton cooled corona in hydrostatic equilibrium in the vertical direction sets an upper limit on the Thomson optical depth \tau_{cor} < 5 . We show this value cannot be exceeded independently of the accretion disk parameters. However, magnetic pressure can extend this result to larger optical depths. Namely, a dissipative corona might have an optical depth up to ~ 20 when the magnetic pressure is 100 times higher that the gas pressure. The observation of warm coronae with Thomson depth larger than ~ 5 puts tights constraints on the physics of the accretion disk/corona systems and requires either strong magnetic fields or vertical outflows to stabilize the system.Comment: 9 pages 6 figure, submitted to A&A, comments are welcom

Intermediate-line Emission in AGNs: The Effect of Prescription of the Gas Density

The requirement of intermediate line component in the recently observed spectra of several AGNs points to possibility of the existence of a physically separate region between broad line region (BLR) and narrow line region (NLR). In this paper we explore the emission from intermediate line region (ILR) by using the photoionization simulations of the gas clouds distributed radially from the AGN center. The gas clouds span distances typical for BLR, ILR and NLR, and the appearance of dust at the sublimation radius is fully taken into account in our model. Single cloud structure is calculated under the assumption of the constant pressure. We show that the slope of the power law cloud density radial profile does not affect the existence of ILR in major types of AGN. We found that the low ionization iron line, Fe~II, appears to be highly sensitive for the presence of dust and therefore becomes potential tracer of dust content in line emitting regions. We show that the use of disk-like cloud density profile computed at the upper part of the accretion disc atmosphere reproduces the observed properties of the line emissivities. In particular, the distance of H${\beta}$ line inferred from our model agrees with that obtained from the reverberation mapping studies in Sy1 galaxy NGC 5548.Comment: 15 pages, 13 figure

The intermediate line region in active galactic nuclei

We show that the recently observed suppression of the gap between the broad line region (BLR) and the narrow line region (NLR) in some AGN can be fully explained by an increase of the gas density in the emitting region. Our model predicts the formation of the intermediate line region (ILR) that is observed in some Seyfert galaxies by the detection of emission lines with intermediate velocity full width half maximum (FWHM) $\sim$ 700 - 1200 km s$^{-1}$. These lines are believed to be originating from an ILR located somewhere between the BLR and NLR. As it was previously proved, the apparent gap is assumed to be caused by the presence of dust beyond the sublimation radius. Our computations with the use of {\sc cloudy} photoionization code, show that the differences in the shape of spectral energy distribution (SED) from the central region of AGN, do not diminish the apparent gap in the line emission in those objects. A strong discontinuity in the line emission vs radius exists for all lines at the dust sublimation radius. However, increasing the gas density to $\sim$ 10$^{11.5}$ cm$^{-3}$ at the sublimation radius provides the continuous line emission vs radius and fully explains the recently observed lack of apparent gap in some AGN. We show that such a high density is consistent with the density of upper layers of an accretion disk atmosphere. Therefore, the upper layers of the disk atmosphere can give rise to the formation of observed emission line clouds.Comment: 9 pages, 6 figures, accepted for publication in Ap

QPO in RE J1034+396: model constraints from observed trends

We analyze the time variability of the X-ray emission of RE J1034+396, an active galactic nucleus with the first firm detection of a quasi-periodic oscillations (QPO). Based on the results of a wavelet analysis, we find a drift in the QPO central frequency. The change inthe QPO frequency correlates with the change in the X-ray flux with a short time delay. Linear structures such as shocks, spiral waves, orvery distant flares seem to be a favored explanation for this particular QPO event.Comment: to appear in the proceedings to "The Central Kiloparsec in Galactic Nuclei (AHAR2011)", Journal of Physics: Conference Series (JPCS), IOP Publishin