Very High-energy Gamma-Ray Episodic Activity of Radio Galaxy NGC 1275 in 2022-2023 Measured with MACE

TL;DR

This paper reports the detection of two high-energy gamma-ray flares from NGC 1275 in 2022-2023, analyzing their spectra and modeling the emission with a synchrotron self-Compton framework to understand the source's variability.

Contribution

First detection of episodic VHE gamma-ray activity from NGC 1275 during 2022-2023 with detailed spectral analysis and modeling.

Findings

The second flare reached 58% of the Crab Nebula flux above 80 GeV.

The energy spectrum follows a power law with index -2.90 ± 0.16.

A homogeneous single-zone SSC model explains the gamma-ray emission and variability.

Abstract

The radio galaxy NGC 1275, located at the central region of Perseus cluster, is a well-known very high-energy (VHE) gamma-ray emitter. The Major Atmospheric Cherenkov Experiment Telescope has detected two distinct episodes of VHE (E > 80 GeV) gamma-ray emission from NGC 1275 during 2022 December and 2023 January. The second outburst, observed on 2023 January 10, was the more intense of the two, with flux reaching 58$\%$ of the Crab Nebula flux above 80 GeV. The differential energy spectrum measured between 80 GeV and 1.5 TeV can be described by a power law with a spectral index of $\Gamma = - 2.90 \pm 0.16_{stat}$ for both flaring events. The broadband spectral energy distribution derived from these flares, along with quasisimultaneous low-energy counterparts, suggests that the observed gamma-ray emission can be explained using a homogeneous single-zone synchrotron self-Compton model. The physical parameters derived from this model for both flaring states are similar. The intermediate state observed between two flaring episodes is explained by a lower Doppler factor or magnetic field, which subsequently returned to its previous value during the high-activity state observed on 2023 January 10.