DA 362: a gamma-ray-emitting compact symmetric object

Abstract

The γ-ray detection from an astrophysical object indicates the presence of an extreme environment where highenergy radiation is produced. With the continuous monitoring of the γ-ray sky by the Fermi Large Area Telescope (LAT) leading to deeper sensitivity, high-energy γ-ray emission has now been detected from a diverse class of jetted active galactic nuclei (AGNs). Here, we present the results of a multiwavelength study of the radio source DA 362, which was reported to be a blazar candidate of uncertain type. However, it was recently identified as a bona fide compact symmetric object (CSO) based on its subkiloparsec, bipolar radio morphology, and lack of radio variability. This makes DA 362 only the fourth γ-ray-emitting object of this enigmatic class of radio-loud AGNs. Using five very-long-baseline interferometry observations covering 1996–2018, we found the jet separation velocity to be subluminal (vapp ~ 0.2c), thus supporting its CSO nature. Its Fermi-LAT observations revealed a γray flaring activity, a phenomenon never detected from the other three γ-ray-detected CSOs. This object is bright in the near-infrared band but extremely faint in the optical-UV filters, hinting at possible obscuration. Swift X-Ray Telescope observation of DA 362 reveals an extremely hard X-ray spectrum, though a strong claim cannot be made due to large uncertainties. We conclude that deeper observations are needed to probe the broadband properties of this enigmatic object and to understand the origin of high-energy γ-ray emission