A Swift X-ray view of the SMS4 sample -- X-ray properties of 31 quasars and radio galaxies

TL;DR

This study uses Swift X-ray observations to analyze the X-ray properties of 31 radio sources from the SMS4 catalog, providing new data on their emission, counterparts, and potential for further observation.

Contribution

First X-ray analysis of 31 SMS4 radio sources with Swift, including detections, spectral analysis, and counterpart identification, expanding knowledge of these bright radio sources.

Findings

20 sources detected in X-ray band

Reliable infrared and optical counterparts for 18 sources

Approximately 35% of sources below 10.9 Jy at 178 MHz

Abstract

We present Swift observations of 31 sources from the SMS4 catalog, a sample of 137 bright radio sources in the Southern Hemisphere. All these sources had no Chandra or XMM-Newton observations: 24 of these were observed with Swift through a dedicated proposal in 2015, and data for the remaining seven were retrieved from the Swift archive. The reduction and analysis of data collected by the Swift X-ray Telescope (XRT) led to 20 detections in the 0.3--10 keV band. We provide details of the X-ray emission in this band for these 20 detections, as well as upper limits for the remaining 11 SMS4 sources. When statistics allowed, we investigated the extent of the X-ray emission, the hardness ratio, and we carried out a spectral analysis. We matched the 20 X-ray detected sources with infrared (AllWISE, CatWISE2020) and optical (GSC 2.3.2, DES DR2) catalogs to establish associations with infrared and optical sources, and compared our results with previously published counterparts in these bands. Requiring a detection in both the infrared and the optical bands to establish a candidate counterpart for our X-ray detections, we obtain reliable counterparts for 18 sources, while the remaining two sources need further investigation to establish firm identifications. We find that ~35% of all the SMS4 sources lie below the lower limit of 10.9 Jy for the flux density at 178 MHz. We present the list of 56 SMS4 sources that in 2022 March remain to be observed in the X-rays with narrow-field instruments.