The First GeV Gamma-Ray Flares from the CSO-like Source 4C 76.03

TL;DR

This paper reports the first detection of GeV gamma-ray flares from the CSO-like source 4C 76.03, revealing transient nuclear activity and offering insights into early radio jet evolution over 17 years of Fermi-LAT data.

Contribution

It presents the first observation of gamma-ray flares from a CSO-like source, indicating active nuclear processes and transitional jet development.

Findings

Detected two gamma-ray flares separated by 2.5 years

Flares occurred on timescales of 20-30 days

Gamma-ray activity suggests ongoing central engine activity

Abstract

We report the first detection of GeV gamma-ray flaring activity from the compact symmetric object (CSO)-like source 4C 76.03, based on 17 years of Fermi-LAT observations. Its long-term, time-averaged gamma-ray properties are consistent with the 4FGL-DR4 catalog. However, a time-resolved analysis with 100-day binning reveals two prominent flares occurring on timescales of approximately 30 days and 20 days, separated by about 2.5 years, with nearly identical fluxes, test statistic (TS) values, and photon indices. The short-timescale variability indicates localized and transient energy dissipation in the nuclear region, likely associated with newly injected jet components. Although the gamma-ray emission does not directly trace the long-term jet power responsible for building the observed radio structure, it demonstrates that the central engine remains active. In the context of CSO evolution, 4C 76.03 may represent a rare transitional case, where repeated energy injections allow the source to exceed the canonical 500 pc scale of most CSOs, providing key insight into the early stages of radio jet evolution.