VLA observations of Fermi unassociated sources


We aim to undertake a detailed examination of every Fermi detected object in the northern sky with declination > +10° deg not yet associated with a known source type (blazar, pulsar, etc.). In the latest Fermi catalogue 2FGL there is still a large number of such sources: 159 objects in this declination zone. For every unassociated Fermi object we will use VLA observations to gather a list of radio sources within the LAT localization error ellipses, and will determine their flux densities, spectral indexes, and morphologies. This will help to increase the number of radio-γ associations, especially in the poorly explored regime of radio-weak AGN. We will find a population of radio silent γ-ray sources or demonstrate that such a population does not exist. Combined with our concurrent ATCA proposal covering the southern hemisphere, radio emission from every unassociated Fermi object will be investigated in detail.

Proposed observations

We propose to observe all \Fermi\ unassociated sources with > +10° with the EVLA at opposite wings of the C-band. We propose to record 4 intemediate frequencies, 1024 MHz wide each, dual polarization, centered at 4.512 GHz and 7.488 GHz. We have reviewed the candidate 2FGL unassociated sources, and removed any sources that have been detected as pulsars and few sources recently observed with the EVLA since the 2FGL catalog release. Each source will be observed in two scans of 60 seconds each. Since the VLA field of view approximately corresponds to a typical 95% Fermi position error ellipse (The 95% 2FGL position error is less than 8.5') we will find all radio sources brighter than 1mJy (conservative estimate) within the Fermi position error and determine their 1) flux densities, 2) radio spectra, and 3) positions with 0.1" accuracy.

This will allow us

The existence of a population of radio weak(silent) γ-ray sources has a potential for interesting discoveries. Recently, Ackermann et al.(2011) proposed a scheme for source classification based on their high energy spectra. Statistical analysis of classification of radio weak sources should help to answer the question what kind of objects they are: radio weak blazars, weak pulsars, or something else.


Team members (in alphabetic order)

Yury Kovalev Astrospace Center, Russia
Justin Linford University of New Mexico, USA
Leonid Petrov Astrogeo Center, USA
Frank Schinzel University of New Mexico, USA
Greg Taylor University of New Mexico, USA

Source list

Map of 2FGL unassociated sources. The area below +10° will not be observed with VLA, but will be observed with ATCA.

Sources in the Current list of targets. Sources marked with # in the first column were not associated in the original 2FGL release, but currently are considered associated owing to new observations.

Current status


  1. Abdo A. A., 2012, ApJS, 119, 31
  2. Ackermann M., 2012, ApJ, 753, 83
  3. Kovalev Y. Y. 2009, ApJ, 707, L56
  4. Petrov L., Kovalev Y. Y., Fomalont E. B., Gordon D. 2008, AJ, 136, 580

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This web page was prepared by Leonid Petrov ()
Last update: 2014.07.23_13:56:35