Multiwavelength monitoring of NGC 1275 over a decade: Evidence of a shift in synchrotron peak frequency and long-term multi-band flux increase

TL;DR

This study of NGC 1275 over 11 years reveals a shift in the synchrotron peak frequency and a long-term increase in multi-band flux, highlighting changes in jet activity and emission mechanisms in this active galaxy.

Contribution

It provides the first detailed long-term multi-wavelength analysis showing a shift in synchrotron peak frequency and flux evolution in NGC 1275.

Findings

Identification of four distinct activity states.

Increase in baseline flux over the first three states.

Detection of a shift in the synchrotron peak frequency during short-term observations.

Abstract

We carried out a detailed study of the temporal and broadband spectral behaviour of one of the brightest misaligned active galaxies in gamma-rays, NGC 1275 utilising 11 years of Fermi, and available Swift and AstroSat observations. Based on the cumulative flux distribution of the gamma-ray lightcurve, we identified four distinct activity states and noticed an increase in the baseline flux during the first three states. Similar nature of the increase in the average flux was also noticed in X-ray and UV bands. A large flaring activity in gamma-rays was noticed in the fourth state. The source was observed twice by AstroSat for shorter intervals (~days) during the longer observing periods (~years) state 3 and 4. During AstroSat observing periods, the source gamma-ray flux was higher than the average flux observed during longer duration states. The increase in the average baseline flux from state 1 to state 3 can be explained considering a corresponding increase of jet particle normalisation. The inverse Comptonisation of synchrotron photons explained the average X-ray and gamma-ray emission by jet electrons during the first three longer duration states. However, during the shorter duration AstroSat observing periods, a shift of the synchrotron peak frequency was noticed, and the synchrotron emission of jet electrons well explained the observed X-ray flux.