454 research outputs found
Central Masses and Broad-Line Region Sizes of Active Galactic Nuclei: I. Comparing the Photoionization and Reverberation Techniques
The masses and emission-line region sizes of Active Galactic Nuclei (AGNs)
can be measured by ``reverberation-mapping'' (measuring the lag of the
emission-line luminosity after changes in the continuum). We use tis technique
to calibrate similar size and mass estimates made by photoionization models of
the AGN line-emitting regions. We compile a sample of 19 AGNs with reliable
reverberation and spectroscopy data, twice the number available previously. The
data provide strong evidence that the BLR size and the emission-line width
measure directly the central mass. Two methods are used to estimate the
distance of the broad emission-line region (BLR) from the ionizing source: the
photoionization method (available for many AGNs but has large intrinsic
uncertainties), and the reverberation method (gives very reliable distances,
but available for only a few objects). The distance estimate is combined with
the velocity dispersion, derived from the broad Hb line profile, to estimate
the virial mass. Comparing the central masses calculated with the reverberation
method to those calculated using a photoionization model, we find a highly
significant, nearly linear correlation. This provides a calibration of the
photoionization method on the objects with presently available reverberation
data, which should enable mass estimates for all AGNs with measured Hb line
width. Comparing the BLR sizes given by the two methods also enables us to
estimate the ionizing EUV luminosity which is directly unobservable. We find it
to be typically ten times the visible (monochromatic luminosity at 5100A). The
inferred Eddington ratio of the individual objects in our sample are 0.001-0.03
(visible luminosity) and 0.01-0.3 (ionizing luminosity).Comment: 27 pages Latex, 8 figures. Accepted for publication in the
Astrophysical Journa
Cosmic ray production in supernova remnants including reacceleration: the secondary to primary ratio
We study the production of cosmic rays (CRs) in supernova remnants (SNRs),
including the reacceleration of background galactic cosmic rays (GCRs) - thus
refining the early considerations by Blandford & Ostriker (1980) and Wandel et
al. (1987) - and the effects of the nuclear spallation inside the sources (the
SNRs). This combines for the first time nuclear spallation inside CR sources
and in the diffuse interstellar medium, as well as reacceleration, with the
injection and subsequent acceleration of suprathermal particles from the
postshock thermal pool. Selfconsistent CR spectra are calculated on the basis
of the nonlinear kinetic model. It is shown that GCR reacceleration and CR
spallation produce a measurable effect at high energies, especially in the
secondary to primary (s/p) ratio, making its energy-dependence substantially
flatter than predicted by the standard model. Quantitatively, the effect
depends strongly upon the density of the surrounding circumstellar matter. GCR
reacceleration dominates secondary CR production for a low circumstellar
density. It increases the expected s/p ratio substantially and flattens its
spectrum to an almost energy-independent form for energies larger than 100
GeV/n if the supernovae explode on average into a hot dilute medium with
hydrogen number density cm. The contribution of CR spallation
inside SNRs to the s/p ratio increases with increasing circumstellar density
and becomes dominant for N_H\gsim 1 cm, leading at high energies to a
flat s/p ratio which is only by a factor of three lower than in the case of the
hot medium. Measurements of the boron to carbon ratio at energies above 100
GeV/n could be used in comparison with the values predicted here as a
consistency test for the supernova origin of the GCRs.Comment: 11 pages, 6 figures, accepted for publication in Astronomy and
Astrophysic
Fractional Models of Cosmic Ray Acceleration in the Galaxy
Possible formulations of the problem of cosmic rays acceleration in the
interstellar galactic medium are considered with the use of fractional
differential equations. The applied technique has been physically justified. A
Fermi result has been generalized to the case of the acceleration of particles
in shock waves in the supernovae remnants fractally distributed in the Galaxy.Comment: 10 page
Short-term emission line and continuum variations in Mrk110
We present results of a variability campaign of Mrk110 performed with the
9.2-m Hobby-Eberly Telescope (HET) at McDonald Observatory. The high S/N
spectra cover most of the optical range. They were taken from 1999 November
through 2000 May. The average interval between the observations was 7.3 days
and the median interval was only 3.0 days. Mrk110 is a narrow-line Seyfert 1
galaxy. During our campaign the continuum flux was in a historically low stage.
Considering the delays of the emission lines with respect to the continuum
variations we could verify an ionization stratification of the BLR. We derived
virial masses of the central black hole from the radial distances of the
different emission lines and from their widths. The calculated central masses
agree within 20%. Furthermore, we identified optical HeI singlet emission lines
emitted in the broad-line region. The observed line fluxes agree with
theoretical predictions. We show that a broad wing on the red side of the
[OIII]5007 line is caused by the HeI singlet line at 5016A.Comment: 11 pages, 16 figures, A&A Latex. Accepted for publication in A&A Main
Journa
Simultaneous EUV and X-ray variability of NGC 4051
We present a flux variability study of simultaneous RXTE and EUVE
observations of the highly variable Seyfert galaxy NGC4051. We find a strong
correlation between variability in the EUV and medium energy X-ray
bands,indicating that both are sampling the same power-law continuum. The lag
between the two bands is less than 20 ks and, depending on model assumptions,
may be <1 ks. We examine the consequences of such a small lag in the context of
simple Comptonisation models for the production of the power-law continuum. A
lag of <1 ks implies that the size of the Comptonising region is less than 20
Schwarzschild radii for a black hole of mass >1E6 solar masses.Comment: 8 pages, accepted for publication in MNRA
Extending the Shakura-Sunyaev approach to a strongly magnetized accretion disc model
We develop a model of thin turbulent accretion discs supported by magnetic
pressure of turbulent magnetic fields. This applies when the turbulent kinetic
and magnetic energy densities are greater than the thermal energy density in
the disc. Whether such discs survive in nature or not remains to be determined,
but here we simply demonstrate that self-consistent solutions exist when the
alpha-prescription for the viscous stress, similar to that of the original
Shakura-Sunyaev model, is used. We show that \alpha \sim 1 for the strongly
magnetized case and we calculate the radial structure and emission spectra from
the disc in the regime when it is optically thick. Strongly magnetized
optically thick discs can apply to the full range of disc radii for objects <
10^{-2} of the Eddington luminosity or for the outer parts of discs in higher
luminosity sources. In the limit that the magnetic pressure is equal to the
thermal or radiation pressure, our strongly magnetized disc model transforms
into the Shakura-Sunyaev model with \alpha=1. Our model produces spectra quite
similar to those of standard Shakura-Sunyaev models. In our comparative study,
we also discovered a small discrepancy in the spectral calculations of Shakura
and Sunyaev (1973).Comment: 27 pages, 11 figures, Astron. Astroph. in press; shortened version
accepted by A&A, all calculations and conclusions are unchange
SDSS J143030.22-001115.1: A misclassified narrow-line Seyfert 1 galaxy with flat X-ray spectrum
We used multi-component profiles to model H and [O III]4959,5007 lines for SDSS J143030.22-001115.1, a narrow-line Seyfert 1
galaxy (NLS1) in a sample of 150 NLS1s candidates selected from the Sloan
Digital Sky Survey (SDSS) Early Data Release (EDR). After subtracting the
H contribution from narrow line regions (NLRs), we found that its full
width half maximum (FWHM) of broad H line is nearly 2900 \kms,
significantly larger than the customarily adopted criterion of 2000 \kms. With
its weak Fe II multiples, we think that SDSS J143030.22-001115.1 can't be
classified as a genuine NLS1. When we calculate the virial black hole masses of
NLS1s, we should use the H linewidth after subtracting the H
contribution from NLRs.Comment: 7 pages, 1 table, accepted by ChJA
Reverberation Mapping of the Intermediate Mass Nuclear Black Hole in SDSS J114008.71+030711.4
We present the results of a reverberation mapping (RM) campaign on the black
hole (BH) associated with the active galactic nucleus (AGN) in SDSS
J114008.71+030711.4 (hereafter GH08). This object is selected from a sample of
19 candidate intermediate mass BHs (M_{BH} < 10^{6} Msun) found by Greene & Ho
2004 in the Sloan Digital Sky Survey (SDSS). We used the Hobby-Eberly Telescope
to obtain 30 spectra over a period of 178 days in an attempt to resolve the
reverberation time lag (tau) between the continuum source and the broad line
region (BLR) in order to determine the radius of the BLR (R_{BLR}) in GH08. We
measure tau to be 2 days with an upper limit of 6 days. We estimate the AGN
luminosity at 5100 Angstroms to be approximately 1.1 x 10^{43} erg s^{-1} after
deconvolution from the host galaxy. The most well calibrated R_{BLR}-L relation
predicts a time lag which is 4 times larger than what we measure. Using the
measured H\beta\ full-width-at-half-maximum of 703 (+/-) 110 km s^{-1} and an
upper limit for R_{BLR} = 6 light days, we find M_{BH} < 5.8 x 10^{5} Msun as
an upper limit to the BH virial mass in GH08, which implies super-Eddington
accretion. Based on our measured M_{BH} we propose that GH08 may be another
candidate to add to the very short list of AGNs with M_{BH} < 10^{6} Msun
determined using RM.Comment: Accepted for publication in ApJ, 21 pages, 5 figures, 3 table
The Black Hole Mass of NGC 4151: Comparison of Reverberation Mapping and Stellar Dynamical Measurements
We present a stellar dynamical estimate of the black hole (BH) mass in the
Seyfert 1 galaxy, NGC 4151. We analyze ground-based spectroscopy as well as
imaging data from the ground and space, and we construct 3-integral
axisymmetric models in order to constrain the BH mass and mass-to-light ratio.
The dynamical models depend on the assumed inclination of the kinematic
symmetry axis of the stellar bulge. In the case where the bulge is assumed to
be viewed edge-on, the kinematical data give only an upper limit to the mass of
the BH of ~4e7 M_sun (1 sigma). If the bulge kinematic axis is assumed to have
the same inclination as the symmetry axis of the large-scale galaxy disk (i.e.,
23 degrees relative to the line of sight), a best-fit dynamical mass between
4-5e7 M_sun is obtained. However, because of the poor quality of the fit when
the bulge is assumed to be inclined (as determined by the noisiness of the
chi^2 surface and its minimum value), and because we lack spectroscopic data
that clearly resolves the BH sphere of influence, we consider our measurements
to be tentative estimates of the dynamical BH mass. With this preliminary
result, NGC 4151 is now among the small sample of galaxies in which the BH mass
has been constrained from two independent techniques, and the mass values we
find for both bulge inclinations are in reasonable agreement with the recent
estimate from reverberation mapping (4.57[+0.57/-0.47]e7 M_sun) published by
Bentz et al.Comment: 20 pages, including 11 low-res figures. Accepted for publication in
ApJ. High resolution version available upon reques
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