70 research outputs found
The colour of the narrow line Sy1-blazar 0324+3410
Aims. We investigate the properties of the host galaxy of the blazar
J0324+3410 (B2 0321+33) by the analysis of B and R images obtained with the NOT
under good photometric conditions. Methods: The galaxy was studied using
different methods: Sersic model fitting, unsharp-masked images, B-R image and
B-R profile analysis. Results: The images show that the host galaxy has a
ring-like morphology. The B-R colour image reveals two bluish zones: one that
coincides with the nuclear region, interpreted as the signature of emission
related to the active nucleus, the other zone is extended and is located in the
host ring-structure. We discuss the hypothesis that the later is thermal
emission from a burst of star formation triggered by an interacting/merging
process
SDSS J124602.54+011318.8: A Highly Variable AGN, Not an Orphan GRB Afterglow
The optically variable source SDSS J124602.54+011318.8 first appears in Sloan
Digital Sky Survey (SDSS) data as a bright point source with nonstellar colors.
Subsequent SDSS imaging and spectroscopy showed that the point source declined
or disappeared, revealing an underlying host galaxy at redshift 0.385. Based on
these properties, the source was suggested to be a candidate ``orphan
afterglow'': a moderately beamed optical transient, associated with a gamma-ray
burst (GRB) whose highly beamed radiation cone does not include our line of
sight. We present new imaging and spectroscopic observations of this source.
When combined with a careful re-analysis of archival optical and radio data,
the observations prove that SDSS J124602.54+011318.8 is in fact an unusual
radio-loud AGN, probably in the BL Lac class. The object displays strong
photometric variability on time scales of weeks to years, including several
bright flares, similar to the one initially reported. The SDSS observations are
therefore almost certainly not related to a GRB. The optical spectrum of this
object dramatically changes in correlation with its optical brightness. At the
bright phase, weak, narrow oxygen emission lines and probably a broader
H line are superposed on a blue continuum. As the flux decreases, the
spectrum becomes dominated by the host galaxy light, with emerging stellar
absorption lines, while both the narrow and broad emission lines have larger
equivalent widths. We briefly discuss the implications of this discovery on the
study of AGNs and other optically variable or transient phenomena.Comment: 14 pages, 5 figures, AASTEX 5.0.2, slight modifications following
referee's report, PASP, in pres
Blazar Counterparts for 3EG Sources at -40 < decl. < 0: Pushing South Through the Bulge
Supplementing existing survey data with VLA observations, we have extended
ray counterpart identifications down to decl. = -40 using our
Figure of Merit approach. We find blazar counterparts for 70% of EGRET
sources above decl. = -40 away from the Galaxy. Spectroscopic
confirmation is in progress, and spectra for two dozen sources are
presented here. We find evidence that increased exposure in the bulge region
allowed EGRET to detect relatively faint blazars; a clear excess of non-blazar
objects in this region however argues for an additional (new) source class.Comment: ApJ accepte
VLBI Polarimetry of 177 Sources from the Caltech-Jodrell Bank Flat-spectrum Survey
We present VLBA observations and a statistical analysis of 5 GHz VLBI
polarimetry data from 177 sources in the Caltech-Jodrell Bank flat-spectrum
(CJF) survey. The CJF survey, a complete, flux-density-limited sample of 293
extragalactic radio sources, gives us the unique opportunity to compare a broad
range of source properties for quasars, galaxies and BL Lacertae objects. We
focus primarily on jet properties, specifically the correlation between the jet
axis angle and the polarization angle in the core and jet. A strong correlation
is found for the electric vector polarization angle in the cores of quasars to
be perpendicular to the jet axis. Contrary to previous claims, no correlation
is found between the jet polarization angle and the jet axis in either quasars
or BL Lac objects. With this large, homogeneous sample we are also able to
investigate cosmological issues and AGN evolution.Comment: Accepted to the Astrophysical Journal: 37 pages, 14 figure
The Gamma-Ray Blazar Content of the Northern Sky
Using survey data, we have re-evaluated the correlation of flat spectrum
radio sources with EGRET sources in the Northern sky. A likelihood analysis
incorporating the radio and X-ray properties and the Gamma-ray source
localization is used to gauge the reliability of associations and to search for
counterparts of previously unidentified EGRET sources. Above |b|=10deg, where
the classification is complete, we find that 70% of the Northern EGRET sources
have counterparts similar to the bright EGRET blazars. For several of these we
identify known blazar counterparts more likely than the earlier proposed 3EG
association; for ~20 we have new identifications. Spectroscopic confirmation of
these candidates is in progress and we have found flat spectrum radio quasars
and BL Lac counterparts with redshifts as high as 4. We also find strong
evidence for a set of 28 objects with no plausible counterpart like the known
EGRET Blazars. These thus represent either a new extragalactic population or a
population of Galactic objects with a large scale height. The survey has been
extended into the plane, where we find several new blazar candidates; the bulk
of the sources are, however, Galactic. Looking ahead to the GLAST era we
predict that several of the present 3EG sources are composite and that higher
resolution data will break these into multiple Blazar IDs.Comment: 13 pages, 6 figures, submitted to Ap
A Parsec Scale Accelerating Radio Jet in the Giant Radio Galaxy NGC315
Observations of the core of the giant radio galaxy NGC315 made with VLBI
interferometers are discussed in the context of a relativistic jet. The
sidedness asymmetry suggests Doppler favoritism from a relativistic jet. The
presence of moving features in the jet as well as jet counter--jet brightness
ratios hint at an accelerating, relativistic jet. An increasing jet velocity is
also supported by a comparison of the jet's observed properties with the
predictions of an adiabatic expansion model. On the parsec scale, the jet is
unpolarized at a wavelength of 6 cm to a very high degree in clear distinction
to the high polarization seen on the kiloparsec scale.Comment: 24 pages with 8 figures. ApJ in pres
WISE colours and star-formation in the host galaxies of radio-loud narrow-line Seyfert 1
We investigate the mid-infrared properties of the largest (42 objects) sample
of radio-loud narrow-line Seyfert 1 (RL NLS1) collected to date, using data
from the Wide-field Infrared Survey Explorer (WISE). We analyse the mid-IR
colours of these objects and compare them to what is expected from different
combinations of AGN and galaxy templates. We find that, in general, the
host-galaxy emission gives an importan contribution to the observed mid-IR flux
in particular at the longest wavelengths (W3, at 12micron, and W4, at
22micron). In about half of the sources (22 objects) we observe a very red
mid-IR colour (W4-W3>2.5) that can be explained only using a starburst galaxy
template (M82). Using the 22micron luminosities, corrected for the AGN
contribution, we have then estimated the star-formation rate for 20 of these
"red" RL NLS1, finding values ranging from 10 to 500 Msun/y. For the RL NLS1
showing bluer colours, instead, we cannot exclude the presence of a
star-forming host galaxy although, on average, we expect a lower star-formation
rate. Studying the radio (1.4GHz) to mid-IR (22micron) flux ratios of the RL
NLS1 in the sample we found that in ~10 objects the star-forming activity could
represent the most important component also at radio frequencies, in addition
(or in alternative) to the relativistic jet. We conclude that both the mid-IR
and the radio emission of RL NLS1 are a mixture of different components,
including the relativistic jet, the dusty torus and an intense star-forming
activity.Comment: Accepted for publication in MNRAS, 11 pages, 7 figures, 2 table
- âŠ