1FGL AGNs at parsec scales (north)
We propose to observe with VLBA+GBT all counterparts from the 1FGL
catalogue of γ-ray sources discovered by Fermi which were not studied
before at parsec scales. Their total flux density at 8 GHz is found
by Abdo et al. (2010b) and our analysis to be in the range of about
1 to 100 mJy. Despite the previous view that -ray detected AGN are
identified with extragalactic objects showing flat radio spectra —
an indicator of a compact boosted relativistic jet — some of these
objects show peaked or even steep radio spectra.
We will observe 155 1FGL counterparts with declination > -30°.
We will extend analysis of AGNs detected by the Fermi LAT and correlate
properties of AGN γ-ray emission with properties of parsec-scale
radio emission. We assume that the AGN -ray emission is generated in the
regions close to the central super-massive black hole, therefore are
interested to compare it with the radio emission from nearby regions.
We eliminate the current VLBI sample bias towards strong radio jets
in order to draw meaningful conclusions from our analysis.
On the basis of our previous analysis (e.g., Kovalev et al. 2009),
we do expect to detect significant parsec-scale emission for most of
the targets. In the same time, the cases of non-detections will provide
a very important basis to test SED models of emission. This project will
deliver the following observational results:
- parsec-scale images of brightness distribution for radio weak
1FGL counterparts or (expected in rare cases) firm upper limits
of parsec-scale flux density,
- parsec-scale characteristics, e.g., flux density, compactness, size,
- positions to the accuracy of better than 10 mas for all VLBI
detected sources. These results will complement similar data
already available for radio strong 1FGL AGNs.
This will allow:
- To perform unbiased studies of both populations of the so-called
blazar's divide (e.g., Ghisellini et al. 2009, Abdo et al. 2010b)
-- the flat-spectrum radio quasars (FSRQ) and BL Lacs. This will
provide constrains on spectrum energy distribution emission models
and test the disk-jet connection for these different types
of blazars. Currently, little parsec-scale information is available
for the Fermi detected BL Lacs since majority of them are radio weak.
For the first time, this project will allow for proper comparison of
1FGL objects with weak and strong parsec-scale radio emission.
- To study parsec-scale properties of the "atypical" objects --
peaked or steep spectrum 1FGL counterparts. Such AGNs were claimed
to be γ-ray quiet on the basis of EGRET results. We will compare
their properties with flat-spectrum radio quasars and check
a hypothesis that all the LAT detected AGNs host a parsec-scale
core -- a strong indicator of an activity happening near the central
super-massive black hole.
- To make the first estimate of an importance of the Doppler boosting
in radio weak 1FGL AGNs on the basis of a statistical analysis
of their parsec-scale properties (brightness temperature and
parsec-scale to kiloparsec-scale flux density ratio).
- To extend the AGN γ-ray -- radio analysis by Abdo et al. (2010b)
to the (most probably, Doppler boosted) parsec scales.
- To allow for deeper follow up VLBI studies of objects of a special
interest by the community providing first VLBI results and
Team members (in alphabetic order):
- Yuri Kovalev
Astro Space Center of Lebedev Physical Institute, Moscow, Russia
- Leonid Petrov
Astrogeo Center, Falls Church, USA
catalogue of positions of 169 detected sources.
Slides of a conference presentation.
Raw cross-correlation data.
NB: The total dataset is about 0.5 Tb. Do not attempt to download the data
unless you know very well what are you doing!
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This web page was prepared by Leonid Petrov
Last update: 2014.08.02_16:33:08