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Title: The Origins of the Gamma-Ray Flux Variations of NGC 1275 Based on Eight Years of Fermi-LAT Observations

Here, we present an analysis of eight years of Fermi-LAT (>0.1 GeV) γ-ray data obtained for the radio galaxy NGC 1275. The γ-ray flux from NGC 1275 is highly variable on short (~days to weeks) timescales, and has steadily increased over this eight year timespan. By examining the changes in its flux and spectral shape in the LAT energy band over the entire data set, we found that its spectral behavior changed around 2011 February (~MJD 55600). The γ-ray spectra at early times evolved largely at high energies, while the photon indices were unchanged at later times despite rather large flux variations. To explain these observations, we suggest that the flux changes at the early times were caused by injection of high-energy electrons into the jet while, later, the γ-ray flares were caused by a changing Doppler factor owing to variations in the jet Lorentz factor and/or changes in the angle to our line of sight. To demonstrate the viability of these scenarios, we fit the broad band spectral energy distribution data with a one-zone synchrotron self-Compton (SSC) model for flaring and quiescent intervals before and after 2011 February. To explain the γ-ray spectral behavior in the context of themore » SSC model, the maximum electron Lorentz factor would have changed at the early times, while a modest change in the Doppler factor adequately fits the quiescent and flaring state γ-ray spectra at the later times.« less
Authors:
ORCiD logo [1] ; ORCiD logo [1] ; ORCiD logo [2] ;  [1] ; ORCiD logo [3] ;  [4] ; ORCiD logo [5]
  1. Waseda Univ., Tokyo (Japan)
  2. Waseda Univ., Tokyo (Japan); Kanazawa Univ., Ishikawa (Japan)
  3. Naval Research Lab., Washington D.C. (United States)
  4. Stanford Univ., Stanford, CA (United States)
  5. Hiroshima Univ., Hiroshima (Japan)
Publication Date:
Grant/Contract Number:
AC02-76SF00515
Type:
Accepted Manuscript
Journal Name:
The Astrophysical Journal (Online)
Additional Journal Information:
Journal Name: The Astrophysical Journal (Online); Journal Volume: 860; Journal Issue: 1; Journal ID: ISSN 1538-4357
Publisher:
Institute of Physics (IOP)
Research Org:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; galaxies: active; galaxies: individual (NGC 1275); galaxies: jets; galaxies: Seyfert; gamma rays: general; radiation mechanisms: non-thermal
OSTI Identifier:
1460993

Tanada, K., Kataoka, J., Arimoto, M., Akita, M., Cheung, C. C., Digel, S. W., and Fukazawa, Y.. The Origins of the Gamma-Ray Flux Variations of NGC 1275 Based on Eight Years of Fermi-LAT Observations. United States: N. p., Web. doi:10.3847/1538-4357/aac26b.
Tanada, K., Kataoka, J., Arimoto, M., Akita, M., Cheung, C. C., Digel, S. W., & Fukazawa, Y.. The Origins of the Gamma-Ray Flux Variations of NGC 1275 Based on Eight Years of Fermi-LAT Observations. United States. doi:10.3847/1538-4357/aac26b.
Tanada, K., Kataoka, J., Arimoto, M., Akita, M., Cheung, C. C., Digel, S. W., and Fukazawa, Y.. 2018. "The Origins of the Gamma-Ray Flux Variations of NGC 1275 Based on Eight Years of Fermi-LAT Observations". United States. doi:10.3847/1538-4357/aac26b.
@article{osti_1460993,
title = {The Origins of the Gamma-Ray Flux Variations of NGC 1275 Based on Eight Years of Fermi-LAT Observations},
author = {Tanada, K. and Kataoka, J. and Arimoto, M. and Akita, M. and Cheung, C. C. and Digel, S. W. and Fukazawa, Y.},
abstractNote = {Here, we present an analysis of eight years of Fermi-LAT (>0.1 GeV) γ-ray data obtained for the radio galaxy NGC 1275. The γ-ray flux from NGC 1275 is highly variable on short (~days to weeks) timescales, and has steadily increased over this eight year timespan. By examining the changes in its flux and spectral shape in the LAT energy band over the entire data set, we found that its spectral behavior changed around 2011 February (~MJD 55600). The γ-ray spectra at early times evolved largely at high energies, while the photon indices were unchanged at later times despite rather large flux variations. To explain these observations, we suggest that the flux changes at the early times were caused by injection of high-energy electrons into the jet while, later, the γ-ray flares were caused by a changing Doppler factor owing to variations in the jet Lorentz factor and/or changes in the angle to our line of sight. To demonstrate the viability of these scenarios, we fit the broad band spectral energy distribution data with a one-zone synchrotron self-Compton (SSC) model for flaring and quiescent intervals before and after 2011 February. To explain the γ-ray spectral behavior in the context of the SSC model, the maximum electron Lorentz factor would have changed at the early times, while a modest change in the Doppler factor adequately fits the quiescent and flaring state γ-ray spectra at the later times.},
doi = {10.3847/1538-4357/aac26b},
journal = {The Astrophysical Journal (Online)},
number = 1,
volume = 860,
place = {United States},
year = {2018},
month = {6}
}