A Non-thermal Study of the Brightest Cluster Galaxy NGC 1275 - The Gamma-Radio Connection Over Four Decades

TL;DR

This study examines four decades of multi-wavelength observations of NGC 1275, revealing complex variability patterns in gamma-ray and radio emissions, and highlighting the importance of broad spectral coverage for understanding active galactic nuclei in galaxy clusters.

Contribution

It provides a comprehensive analysis of long-term variability in NGC 1275 across gamma-ray and radio bands, linking short-term flaring to jet processes and long-term changes to black hole fueling.

Findings

Gamma-ray flaring correlates with high-frequency radio emission on long timescales.

Short-term gamma-ray flares do not affect 1.3 mm flux, indicating different emission regions.

Long-term variability suggests a 30-40 year cycle in black hole fueling.

Abstract

Emission from the active nucleus in the core of the brightest cluster galaxy of the Perseus cluster, NGC 1275, has varied dramatically over the past four decades. Prompted by the Fermi detection of flaring in the gamma-ray band, we present the recent increased activity of this source in the context of its past radio and gamma-ray output. The broad correspondence between the high-frequency radio data and the high-energy (HE) emission is striking. However, on short timescales this correlation breaks down and the 1.3 mm Submillimeter Array flux is apparently unaffected during Fermi-detected flaring activity. The fact that NGC 1275 is also detected at TeV energies during the periods of HE gamma-ray flaring suggests that the short-timescale variation might be primarily related to changes in the inverse Compton scattering of photons by the electron population in the jet. The longer-timescale changes suggest a 30--40 year variation in the fuelling of the black hole, that affects the power of the inner jet. NCG 1275 is a laboratory for the class of brightest cluster galaxies, and its variability on these timescales has implications for our understanding of massive galaxies in cooling-core clusters. The case of NGC 1275 highlights the need for wide coverage across the radio band to correctly account for the contribution to emission from a synchrotron self-absorbed core (for example when considering contamination of Sunyaev-Zel'dovich effect observations), and the danger of variability biases in radio surveys of galaxies.