218 research outputs found
RX J1643.7+3402: a new bright cataclysmic variable
We report the discovery of a new bright (V12.6) cataclysmic variable star identified with the ROSAT X-ray source RX J1643.7+3402. Spectroscopic and photometric observations show it to be a novalike variable sharing some of the characteristics of the SW Sex sub-class of novalike CVs. The spectroscopic period may be either 2\fh575 or 2\fh885, within the period "gap." A photometric modulation with a probable period of 2\fh595 and an amplitude of 0.1 mag in V is present on most nights and could be either a "positive" or a "negative" superhump modulation (depending on the exact spectroscopic period), indicating the presence of a precessing accretion disk in this system. Rapid variations of 0.1 to 0.2 mag amplitude in V repeat with a time scale of 15 min
The optical emission line spectrum of Mark 110
We analyse in detail the rich emission line spectrum of Mark 110 to determine
the physical conditions in the nucleus of this object, a peculiar NLS1 without
any detectable Fe II emission associated with the broad line region and with a
line ratio unusually large for a NLS1. We use 24 spectra
obtained with the Marcario Low Resolution Spectrograph attached at the prime
focus of the 9.2 m Hobby-Eberly telescope at the McDonald observatory. We
fitted the spectrum by identifying all the emission lines (about 220) detected
in the wavelength range 4200-6900 \AA (at rest). The narrow emission lines are
probably produced in a region with a density gradient in the range
10 cm with a rather high column density (5
cm). In addition to a narrow line system, three major broad line systems
with different line velocity and width are required. We confirm the absence of
broad Fe II emission lines. We speculate that Mark 110 is in fact a BLS1 with
relatively "narrow" broad lines but with a BH mass large enough compared to its
luminosity to have a lower than Eddington luminosity.Comment: 13 pages, 5 figures, accepted by A&
Molecular gas in QSO host galaxies
We present the results of a survey for CO line emission from a sample of
nearby QSO hosts taken from the Hamburg/ESO survey (HES) and the Veron-Cetty
and Veron quasar catalogue. From a total of 39 observed sources we clearly
detected 5 objects with >10sigma signals (HE 0108-4743, HE 0224-2834,
J035818.7-612407, HE 1029-1831, HE 2211-3903). Further 6 sources show marginal
detections on the 2sigma level.Comment: 4 pages, 1 figure, submitted to "QSO Hosts: Evolution and
Environment", P.D. Barthel, D.B. Sanders, eds., August 2005, Leiden
University (The Netherlands), New Astr. Re
FE II EMISSION IN AGN
RESUMEN El espectroĂłptico de las galaxias Seyfert 1 muestra una gran variedad de lĂneas de emisiĂłn producidas por FeII. Damos tres ejemplos e investigamos la formaciĂłn de estas lĂneas con el fin de determinar las condiciones fĂsicas de las regiones en donde se emiten. ABSTRACT The optical spectrum of Seyfert 1s reveals a great variety of Fe II emission lines. We give three examples and investigate the formation of these lines in order to determine the physical conditions of the emission regions
Optically bright Active Galactic Nuclei in the ROSAT-Faint Source Catalogue
To build a large, optically bright, X-ray selected AGN sample we have
correlated the ROSAT-FSC catalogue of X-ray sources with the USNO catalogue
limited to objects brighter than O=16.5 and then with the APS database. Each of
the 3,212 coincidences was classified using the slitless Hamburg spectra. 493
objects were found to be extended and 2,719 starlike. Using both the extended
objects and the galaxies known from published catalogues we built up a sample
of 185 galaxies with O_APS < 17.0 mag, which are high-probability counterparts
of RASS-FSC X-ray sources. 130 galaxies have a redshift from the literature and
for another 34 we obtained new spectra. The fraction of Seyfert galaxies in
this sample is 20 %. To select a corresponding sample of 144 high-probability
counterparts among the starlike sources we searched for very blue objects in an
APS-based color-magnitude diagram. Forty-one were already known AGN and for
another 91 objects we obtained new spectra, yielding 42 new AGN, increasing
their number in the sample to 83. This confirms that surveys of bright QSOs are
still significantly incomplete. On the other hand we find that, at a flux limit
of 0.02 count /-1 and at this magnitude, only 40 % of all QSOs are detected by
ROSAT.Comment: 17 pages, 16 figures, accepted by A&
The nature of the absorbing torus in compact Radio Galaxies
We present BeppoSAX observations of the two radio galaxies PKS 1934-63 and S5
1946+708. Strong Iron Kalpha lines are detected in both objects indicating that
the two sources are absorbed by column densities higher than 10^24 cm^(-2).
Combining radio continuum, HI absorption and X-ray data we can constrain the
physical state and the dimensions of the absorber. We find that the putative
obscuring torus is molecular and located at a distance higher than 20 pc from
the center in S5 1946+70. In PKS 1934-63 no radio nucleus has been observed. If
this is due to free-free absorption a radius of only a few pc is inferred.
Since the Kalpha lines have been detected only at 90% confidence, we also
discuss the implications if they would be not as strong as found from our data.
From our results it appears that the combination of hard X-ray data and
spatially resolved HI absorption measurements provides a powerful diagnostic
for conditions in the absorbing ``torus''.Comment: 8 pages, 5 figures, accepted for publication in Astronomy &
Astrophysic
Diagnostics of the structure of AGN's broad line regions with reverberation mapping data: confirmation of the two-component broad line region model
We re-examine the ten Reverberation Mapping (RM) sources with public data
based on the two-component model of the Broad Line Region (BLR). In fitting
their broad H-beta lines, six of them only need one Gaussian component, one of
them has a double-peak profile, one has an irregular profile, and only two of
them need two components, i.e., a Very Broad Gaussian Component (VBGC) and an
Inter-Mediate Gaussian Component (IMGC). The Gaussian components are assumed to
come from two distinct regions in the two-component model; they are Very Broad
Line Region (VBLR) and Inter-Mediate Line region (IMLR). The two sources with a
two-component profile are Mrk 509 and NGC 4051. The time lags of the two
components of both sources satisfy ,
where and are the lags of the two components while
and represent the mean gas velocities of the two regions,
supporting the two-component model of the BLR of Active Galactic Nuclei (AGN).
The fact that most of these ten sources only have the VBGC confirms the
assumption that RM mainly measures the radius of the VBLR; consequently, the
radius obtained from the R-L relationship mainly represent the radius of VBLR.
Moreover, NGC 4051, with a lag of about 5 days in the one component model, is
an outlier on the R-L relationship as shown in Kaspi et al. (2005); however
this problem disappears in our two-component model with lags of about 2 and 6
days for the VBGC and IMGC, respectively.Comment: 7 pages, 5 figures. Accepted for publication in the Special Issue of
Science in China (G) "Astrophysics of Black holes and Related Compact
Objects
Missing baryons and the soft X-ray background
The X-ray background intensity around Lick count galaxies and rich clusters
of galaxies is investigated in three ROSAT energy bands. It is found that the
X-ray enhancements surrounding concentrations of galaxies exhibit significantly
softer spectrum than the standard cluster emission and the average
extragalactic background. The diffuse soft emission accompanying the galaxies
is consistent with the thermal emission of the hot gas postulated first by the
Cen & Ostriker hydrodynamic simulations. Our estimates of the gas temperature -
although subject to large uncertainties - averaged over several Mpc scales are
below 1 keV, which is substantially below the temperature of the intra-cluster
gas, but consistent with temperatures predicted for the local intergalactic
medium. It is pointed out that the planned ROSITA mission would be essential
for our understanding of the diffuse thermal component of the background.Comment: AA accepted, 6 pages, incl. 4 figure
Ultra-High Energy Cosmic Rays Detected by the Pierre Auger Observatory: First Direct Evidence, and its Implications, that a Subset Originate in Nearby Radiogalaxies
(abridged) The Pierre Auger Collaboration has reported 27 Ultra-High Energy
Cosmic Ray Events (UHECRs) with energies above 56 EeV and well determined
arrival directions as of 2007 August 31. They find that the arrival directions
are not isotropic, but instead appear correlated with the positions of nearby
AGNs. Our aim was to determine the sources of these UHECRs by comparing their
arrival directions with more comprehensive source catalogs.
Four (eight) of the 27 UHECRs with energy >56EeV detected by the Pierre Auger
Observatory have arrival directions within 1.5deg (3.5deg) of the extended
(>180kpc) radio structures of nearby radiogalaxies or the single nearby BLLac
with extended radio structure. Conversely the radio structures of three (six)
of all ten nearest extended radiogalaxies are within 1.5deg (3.5deg) of a
UHECR; three of the remaining four radiogalaxies are in directions with lower
exposure times. This correlation between nearby extended radiogalaxies and a
subset of UHECRs is significant at the 99.9% level. This is the first direct
observational proof that radio galaxies are a significant source of UHECRs. For
the remaining ~20 UHECRs, an isotropic distribution cannot be ruled out at high
significance. The correlation found by the Auger Collaboration between the 27
UHECRs and AGNs in the Veron-Cetty & Veron catalog at D < 71Mpc has a much
lower significance when one considers only the ~20 UHECRs not `matched' to
nearby extended radiogalaxies. No correlation is seen between UHECRs and
supernovae, supernova remnants, nearby galaxies, or nearby groups and clusters
of galaxies. The primary difference between the UHECR detections at the Pierre
Auger Observatory and previous experiments may thus be that the Southern
Hemisphere is more privileged with respect to nearby extended radiogalaxies.Comment: 10 pages total. To appear in A&
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