The MAVERIC Survey: Radio catalogs and source counts from deep Very Large Array imaging of 25 Galactic globular clusters

TL;DR

The MAVERIC survey provides deep radio imaging of 25 Galactic globular clusters, detecting nearly 1300 sources and identifying potential compact binaries, including millisecond pulsars, with implications for understanding cluster populations.

Contribution

This is the first deep radio continuum survey of Milky Way globular clusters, offering detailed source catalogs, classifications, and background source counts.

Findings

Detected nearly 1300 radio sources at 5 sigma in 25 clusters.

Found bimodal spectral index distribution indicating different source types.

Identified candidate millisecond pulsars and binaries based on spectral properties.

Abstract

The MAVERIC survey is the first deep radio continuum imaging survey of Milky Way globular clusters, with a central goal of finding and classifying accreting compact binaries, including stellar-mass black holes. Here we present radio source catalogs for 25 clusters with ultra-deep Karl G. Jansky Very Large Array observations. The median observing time was 10 hr per cluster, resulting in typical rms sensitivities of 2.3 and 2.1 uJy per beam at central frequencies of 5.0 and 7.2 GHz, respectively. We detect nearly 1300 sources in our survey at 5 sigma, and while many of these are likely to be background sources, we also find strong evidence for an excess of radio sources in some clusters. The radio spectral index distribution of sources in the cluster cores differs from the background, and shows a bimodal distribution. We tentatively classify the steep-spectrum sources (those much brighter at 5.0 GHz) as millisecond pulsars and the flat-spectrum sources as compact or other kinds of binaries. These provisional classifications will be solidified with the future addition of X-ray and optical data. The outer regions of our images represent a deep, relatively wide field (~ 0.4/sq. deg) and high resolution C band background survey, and we present source counts calculated for this area. We also release radio continuum images for these 25 clusters to the community.