A non-thermal study of the brightest cluster galaxy NGC 1275 – the Gamma-Radio connection over four decades

• Published in: Monthly notices of the Royal Astronomical Society Vol. 442; no. 3; pp. 2048 - 2057
• Main Authors: Dutson, K. L., Edge, A. C., Hinton, J. A., Hogan, M. T., Gurwell, M. A., Alston, W. N.
• Format: Journal Article
• Language: English
• Published: London Oxford University Press 11-08-2014
• Subjects: Gamma ray astronomy; Radiation; Stars & galaxies; radiation mechanisms: non-thermal; galaxies: clusters: individual: Perseus; gamma rays: galaxies; galaxies: active; galaxies: individual: NGC 1275; radio continuum: galaxies
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stu975

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 γ-ray band, we present the recent increased activity of this source in the context of its past radio and γ-ray output. The broad correspondence between the high-frequency radio data and the high-energy (HE) emission is striking. However, on short time-scales 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 γ-ray flaring suggests that the short-time-scale variation might be primarily related to changes in the inverse Compton scattering of photons by the electron population in the jet. The longer-time-scale 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 time-scales 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.