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

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) ∝ να. The maximum of the spectral index distribution is at α = −1, which is characteristic of nonthermal emitters and might indicate an extragalactic population.

Megahertz emission of massive early-type stars in the Cygnus region

“…The fields of view of Giant Metrewave Radio Telescope are 81 ± 4 and 43 ± 3 at 325 and 610 MHz, respectively. a Additional details in the observing process, like FoV centres, exact dates of observation, and name of calibrators used are given in Benaglia et al (2020). The data were reduced by means of the Source Peeling and Atmospheric Modeling (SPAM) routines (Intema 2014).…”

Radio Counterparts of Gamma-Ray Sources in the Cygnus Region

“…The observed area covers ∼20 sq deg, centred at RA, Dec(J2000) = 20:25:30, 42:00:00. It encompasses the stellar association of Cyg OB2, and part of Cyg OB8 and OB9, extremely rich in OB stars and with traces of recent star formation (see Figure 2 by Benaglia et al 2020b).…”

“…The field of views (FoV) of the GMRT are 81±4 and 43±3 (GMRT Observer's Manual 2 ) at 325 MHz and 610 MHz bands respectively. According to the FoVs sizes and the region to cover (see Figure 1), we implemented five pointings at 325 MHz and 47 pointings at 610 MHz (45 plus repeating two additional with originally bad data; again, see Figure 2 of Benaglia et al 2020b), and taking also into account the requirement to obtain a uniform noise with the minimum amount of pointings. The flux calibrators 3C286 and/or 3C48 were observed at the beginning and at the end of the observing session.…”

“…The data was processed with the Source Peeling and Atmospheric Modeling algorithms (Intema 2014), that handle both the calibration and the imaging steps. Full description of acquisition, reduction and imaging of the data is presented with all details in Benaglia et al (2020b). At imaging, we adopted a robust weighting equal to −1.…”

“…We surveyed a highly populated area of the northern sky nearby the Galactic plane at two bands centred at decimetre wavelengths, using the Giant Metrewave Radio Telescope (GMRT). This work is part of a series of studies of the same celestial area in the Cygnus region, mainly the catalog introduced in Benaglia et al (2020b). The latter lists radio sources at 610 MHz and 325 MHz bands, for flux densities greater or equal to 7σ, where σ is the local rms; see also Ishwara-Chandra et al (2019); Benaglia et al (2020a); Isequilla et al (2020).…”