Fukazawa, YasushiShiki, KenseiTanaka, YasuyukiItoh, RyosukeTakahashi, HiromitsuImazato, FumiyaDutka, FilippoOjha, RoopeshNagai, Hiroshi2020-05-112020-05-112018-03-12Yasushi Fukazawa et al., X-Ray and GeV Gamma-Ray Variability of the Radio Galaxy NGC 1275, The Astrophysical Journal, Volume 855, Number 2, doi: https://doi.org/10.3847%2F1538-4357%2Faaabc0https://doi.org/10.3847%2F1538-4357%2Faaabc0http://hdl.handle.net/11603/18538http://simbad.u-strasbg.fr/simbad/sim-ref?querymethod=bib&simbo=on&submit=submit+bibcode&bibcode=2018ApJ...855...93Fhttps://ui.adsabs.harvard.edu/link_gateway/2018ApJ...855...93F/XMMhttps://ned.ipac.caltech.edu/cgi-bin/objsearch?search_type=Search&refcode=2018ApJ...855...93Fhttps://heasarc.gsfc.nasa.gov/xamin/xamin.jsp?bibcode=2018ApJ%2E%2E%2E855%2E%2E%2E93FWe analyzed Suzaku/XIS data (2006–2015) and Fermi/LAT data (2008–2015) of the gamma-ray emitting radio galaxy NGC 1275. Correlated brightening of the nucleus in both the X-ray and GeV gamma-ray energy bands was found for the period 2013–2015. This is the first evidence of correlated variability between these two energy bands for NGC 1275. We also analyzed Swift/XRT data and found that the X-ray flux increased over several days in 2010, coincidentally with the GeV gamma-ray flare. During the flare, the X-ray spectra were softer, with a photon index of ~2 compared with 1.5–2.1 of the other periods, suggesting the brightening of a synchrotron component. The GeV gamma-ray band also showed a higher flux with a harder spectrum during the 2010 flare. Simultaneous X-ray and GeV gamma-ray flux increase in the flare could be explained by the shock-in-jet scenario. On the other hand, a long-term gradual brightening of radio, X-ray, and GeV gamma-ray flux with a larger gamma-ray amplitude could have an origin other than internal shocks, and some of these possibilities are discussed.8 pagesen-USThis item is likely protected under Title 17 of the U.S. Copyright Law. Unless on a Creative Commons license, for uses protected by Copyright Law, contact the copyright holder or the author.© 2018. The American Astronomical Society. All rights reserved.Text