Fermi Gamma-ray Space Telescope

Long-term study of a gamma-ray emtting radio galaxy NGC 1275

Yasushi Fukazawa


NGC 1275 (3C84, Per A) is a famous radio galaxy, sitting at the center of the Perseus cluster. Radio long-term history revealed a dramatic change of flux. Fermi/LAT detected a GeV gamma-ray from NGC 1275 during the first 3 month. The GeV gamma-ray flux is the highest among radio galaxies, and thus we can monitor a gamma-ray flux variability with a time scale of days. The SED of NGC 1275 is roughly represented by one-zone SSC model, but origin of optical and X-ray emission was unclear; jet or disk/corona emission. Therefore, study of time variability is important to decompose emission components. Before 2012, the gamma-ray flux varied but the average flux was almost constant. Sometimes TeV gamma-ray was also detected with MAGIC. After 2012, GeV gamma-ray has gradually increased, together with radio flux, and this increasing component is likely to come from the radio C3 spot. Suzaku long-term monitoring also revelaed a similar X-ray flux increase. Therefore, jet emission should contribute to all energy band. Behavior of gamma-ray variability also changed berore/after 2012, but the origin was not understood. On the other hand, detection of X-ray Fe-K line requires a non-beamed emission like disk/corona emission. Therefore, NGC 1275 is interesting and important to study disk-jet connection by a long-term study. NGC 1275 has sometimes showed a gamma-ray rapid flare with a time scale of several days, and the gamma-ray spectrum became harder during flare, indicating a freshly accelerating electrons by shocks. In the near future, CTA can measure a TeV gamma-ray emission in detail, and thus long-term multi-wavelength study of NGC 1275 is still important to clarify unresolved issues on radio galaxies.