The ATCA c1730 program

There are thought to be about a hundred thousand million galaxies in the observable Universe, yet only about three thousand of these have been detected to emit gamma-rays. The Fermi gamma-ray satellite, launched in June 2008, is revealing more and more of these powerful galaxies, and we are using the Australia Telescope Compact Array (ATCA) to study them at radio wavelengths in order to understand exactly what powers these fascinating objects. Fermi is completing a full-sky survey every three hours and providing unprecedented views of the gamma-ray universe. This project is observing a selection of several hundred active galaxies detected by Fermi which, together with optical, X- ray and Very Long Baseline Interferometry (VLBI) data (from the TANAMI project will enable correlations in the multi-wavelength variability of these objects to be identified and a better understanding gained of the physical processes powering these AGN.

ATCA observations are (from April 2009) made at 5.5, 9, 17, 19, 38 and 40 GHz, using the 2GHz bandwidth provided by the Compact Array Broadband Backend (CABB) at each frequency. The observations are made in "snapshot" mode, with a single scan at each frequency. This observing mode is well-suited to bright compact radio-sources, such as those being studied in this program. Data from c1730 are processed in a data reduction and immediately incorporated in the ATCA calibrator database for use by all astronomers.

While c1730 focuses on monitoring identified Fermi sources, the complementary ATCA proposal C2624 is approaching this question from a different angle, making ATCA observations of the fields of unassociated 2FGL sources, see the AOFUS webpage for more details of that program.

Publications including C1730 data include:

• "Gamma-Ray Eclipses and Orbital Modulation Transitions in the Candidate Redback 4FGL J1702.7-5655," Corbet et al. 2022, Astrophysical Journal, 935, 2
• "The first GeV flare of the radio-loud narrow-line Seyfert 1 galaxy PKS 2004-447," Gokus et al. 2021, Astronomy & Astrophysics, 649, A77
• "Do RadioAstron detections correlate with flaring states? An initial study of seven southern AGN," Edwards et al. 2020, Advances in Space Science, 65, 739
• "Discovery of the Galactic High-mass Gamma-Ray Binary 4FGL J1405.1-6119," Corbet et al. 2019, Astrophysical Journal, 884, 93
• "PKS 1954-388: RadioAstron Detection on 80,000km Baselines and Multiwavelength Observations,'' Edwards et al. 2017, Publications of the Astronomical Society of Australia, 34, 21
• "Multiband Observations of the Quasar PKS 2326-502 during Active and Quiescent Gamma-Ray States in 2010--2012," Dutka et al. 2017, Astrophysical Journal, 835, 182
• "The TANAMI Multiwavelength Program: Dynamic SEDs of Southern Blazars," Krauss et al. 2016, Astronomy & Astrophysics, 591, A130
• "The Gamma-Ray Emitting Radio-Loud Narrow-Line Seyfert 1 Galaxy PKS 2004$-$447: II. The Radio View," Schulz et al. 2016, Astronomy & Astrophysics, 588, A146
• "Peculiar flaring activity in blazar PKS 1424-418 during 2008--2011" Buson et al., 2014, Astronomy & Astrophysics, 569, A40
• "Fermi LAT detection of two high Galactic latitude gamma-ray sources, Fermi J1049.7+0435 and J1103.2+1145,'' Nishimichi et al., 2014, Astrophysical Journal, 783, 94
• "The unusual multiwavelength properties of the gamma-ray source PMN J1603-4904" Mueller et al., 2014, Astronomy & Astrophysics, 562, A4
• "Multi-wavelength Observations of PKS 2142-758 during Active and Quiescent Gamma-Ray States", Dutka et al. 2013, ApJ, 779, 174
• "Hunting for treasures among the Fermi unassociated sources: a multi-wavelength approach" Acero et al. 2013, ApJ, 779, 133
• "H.E.S.S and Fermi-LAT discovery of gamma rays from the blazar 1ES 1312-423" Abramowski et al. 2013, MNRAS, 434, 1889
• "PKS 2123-463: a confirmed gamma-ray blazar at high redshift," D'Ammando et al. 2012, MNRAS 427, 893
• "ATCA monitoring of gamma-ray loud AGN," Stevens et al. 2012, Fermi & Jansky conference
• "Multi-wavelength Observations of PKS 2142-758 during an Active Gamma-Ray State," Dutka et al. 2012, Fermi & Jansky conference
• "The Gamma-Ray Blazar PKS 0208-512, a Multi-Wavelength Investigation," Blanchard et al. 2012, Fermi & Jansky conference
• "High resolution rapid response observations of compact radio sources with the Ceduna Hobart Interferometer (CHI)," Blanchard et al. 2012, A&A, 538, A150

Illustrative multi-epoch results from C1730 are shown in Figures below. The contrasting spectral evolutions of PKS0454-234 and PKS1730--130 are apparent: PKS0454-234 is effectively constant in the 7mm band, with the flux densities decaying at lower frequencies. PKS1730-130, however, shows pronounced variation in all bands, with a quiescent flat spectrum in the first epoch, an inverted spectrum at the higher frequencies in the second epoch, and a steeper spectrum in the third epoch as the flare emission evolves from higher to lower frequencies. This behaviour would be expected to be accompanied by the emergence of a new jet-component on VLBI scales, and increased gamma-ray activity (however as the peak is likely to have occurred before the Fermi launch, this particular case cannot by verified).

A summary of observations made to date is provided in the table below.

For further information on the c1730 program, please contact Phil Edwards (philip . edwards [at] csiro . au).

This page last modified 15-jun-2018.