Study sheds more light on the nature of compact symmetric object DA 362

Indian astronomers have performed a multiwavelength study of a gamma-ray emitting compact symmetric object known as DA 362. Results of the study, presented in a research paper published December 17 on the pre-print server arXiv, yield more insights into the nature of this enigmatic object.

Compact symmetric objects (CSOs) are young jetted active galactic nuclei (AGN) with an overall projected size below 3,300 light years. Although CSOs are still not well investigated, observations found that they showcase symmetric radio morphologies and are likely to be in the early stages of their evolution with kinematic ages smaller than a few thousand years. To date, only four CSOs have been found to emit gamma-rays.

The newest gamma-ray emitting CSO is DA 362, also known as B2 1413+34. It was initially classified as a blazar candidate of uncertain type, associated with a gamma-ray source designated 4FGL J1416.0+3443.

Recently, a team of astronomers led by Subhashree Swain of the Inter-University Center for Astronomy and Astrophysics in Pune, India, has analyzed long-term multiwavelength data regarding DA 362 from the Large Area Telescope (LAT) onboard NASA's Fermi gamma-ray space telescope and from NASA's Swift satellite. The analysis allowed them to investigate the nature of this CSO.

"In this work, we have studied the multiwavelength properties of a CSO DA 362, which was recently found to be a gamma-ray emitter by the Fermi-LAT, thereby making it only the fourth gamma-ray detected object of this class of AGN," the researchers wrote.

The analysis of the LAT data confirmed the association of the gamma-ray source 4FGL J1416.0+3443 with DA 362. It turned out that the optimized gamma-ray position was consistent with the radio source within the estimated 95 percent gamma-ray uncertainty region.

The gamma-ray light curve of DA 362 shows that the source remained mostly in quiescence during the first 12 years of LAT observations (between 2008 and 2020). However, the observations also revealed a flaring activity of DA 362, which suggests that the gamma-ray emission originates most likely from its core or jet rather than from the radio lobes.

Furthermore, the study detected small, parsec-scale, bi-polar radio emission of DA 362 and found that its jet separation velocity is subluminal. These findings confirm DA 362 as a true compact symmetric object.

By comparing the gamma-ray spectral properties with the other three known gamma-ray emitting CSOs, the astronomers found that DA 362 is the brightest among them and exhibits a spectrum steeper than the other sources.

However, it turned out that DA 362 is extremely faint in the optical band, which suggests possible dust obscuration.

The authors of the paper note that deeper observations with sensitive observing facilities should be conducted in order to explore the broadband physical properties of this CSO and to further probe the origin of its gamma-ray emission.

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