Cygnus survey with the Giant Metrewave Radio Telescope at 325 and 610 MHz: the catalog^⋆

¹ Instituto Argentino de Radioastronomía, CONICET & CICPBA, CC5 (1897) Villa Elisa, Prov. de Buenos Aires, Argentina
e-mail: paula@iar.unlp.edu.ar
² Facultad de Ciencias Astronómicas y Geofísicas, UNLP, Paseo del Bosque s/n, 1900 La Plata, Argentina
³ National Centre for Radio Astrophysics (NCRA-TIFR), Pune 411 007, India
⁴ International Centre for Radio Astronomy Research, Curtin University, Bentley, WA 6102, Australia
⁵ Leiden Observatory, Leiden University, Niels Bohrweg 2, 2333 CA Leiden, The Netherlands
⁶ Comisión Nacional de Actividades Espaciales, Paseo Colón 751, (1063) CABA, Argentina
⁷ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany

Received: 8 March 2020
Accepted: 23 July 2020

Abstract

Context. Observations at the radio continuum band below the gigahertz band are key when the nature and properties of nonthermal sources are investigated because their radio radiation is strongest at these frequencies. The low radio frequency range is therefore the best to spot possible counterparts to very high-energy (VHE) sources: relativistic particles of the same population are likely to be involved in radio and high-energy radiation processes. Some of these counterparts to VHE sources can be stellar sources.

Aims. The Cygnus region in the northern sky is one of the richest in this type of sources that are potential counterparts to VHE sources. We surveyed the central ∼15 sq deg of the Cygnus constellation at the 325 and 610 MHz bands with angular resolutions and sensitivities of 10″ and 6″, and 0.5 and 0.2 mJy beam⁻¹, respectively.

Methods. The data were collected during 172 h in 2013–2017, using the Giant Metrewave Radio Telescope with 32 MHz bandwidth, and were calibrated using the SPAM routines. The source extraction was carried out with the PyBDSF tool, followed by verification through visual inspection of every putative catalog candidate source in order to determine its reliability.

Results. In this first paper we present the catalog of sources, consisting of 1048 sources at 325 MHz and 2796 sources at 610 MHz. By cross-matching the sources from both frequencies with the objects of the SIMBAD database, we found possible counterparts for 143 of them. Most of the sources from the 325-MHz catalog (993) were detected at the 610 MHz band, and their spectral index α was computed adopting S(ν) ∝ ν^α. The maximum of the spectral index distribution is at α = −1, which is characteristic of nonthermal emitters and might indicate an extragalactic population.