Discovery of $\gamma$-ray emission from steep radio spectrum NLS1s

TL;DR

This study reports the first detection of gamma-ray emissions from steep radio spectrum Narrow Line Seyfert 1 galaxies, suggesting the presence of misaligned or underdeveloped relativistic jets, and provides insights into jet formation and evolution.

Contribution

It is the first systematic analysis of 7-year Fermi LAT data revealing gamma-ray emissions in this class, expanding the known gamma-ray NLS1s from 7 to 9.

Findings

Detected gamma-ray emissions in two S-NLS1s, increasing known gamma-ray NLS1s to 9.

Found no significant variability in multiwavelength observations.

Suggests these sources have misaligned or underdeveloped relativistic jets.

Abstract

Narrow line Seyfert 1 galaxies (NLS1s) usually do not host relativistic jets and the detection of their $\gamma$-ray emissions is rarely reported. Evidences for strong relativistic beaming effect have been found in all $\gamma$-ray NLS1s to date and hence their jets are believed to be closely aligned. In this work we perform a systematic analysis of 7-year {\it Fermi} Large Area Telescope (LAT) data of 18 steep radio spectrum NLS1s (S-NLS1s) and report the {\it first} two detections of $\gamma$-ray emissions in this class, increasing the total number of known $\gamma$-ray NLS1s to 9. A strong and stable $\gamma$-ray signal (over 8$\sigma$) is produced by SDSS J144318.56+472556.7, and a significant $\gamma$-ray emission (4.5$\sigma$) of SDSS J130522.74+511640.2 has been detected in a monthly flare in November 2013. A thorough investigation of their multiwavelength properties from radio to X rays has been performed, finding no significant variability. Along with their spectral energy distributions and the radio morphology, these facts strongly suggest that these two sources harbor mis-aligned and possibly underdeveloped relativistic jets, which provides valuable targets to reveal the formation and evolution of relativistic jets under extreme circumstances.