Constraining the location of rapid gamma-ray flares in the flat spectrum radio quasar 3C 273
Abstract
We present a γ-ray photon flux and spectral variability study of the flat-spectrum radio quasar 3C 273 over a rapid flaring activity period between September 2009 to April 2010. Five major flares were observed in the source during this period. The most rapid flare observed in the source has a flux doubling time of 1.1 hr. The rapid γ-ray flares allow us to constrain the location and size of the γ-ray emission region in the source. The γγ-opacity constrains the Doppler factor δγ ≥ 10 for the highest energy (15 GeV) photon observed by the Fermi-Large Area Telescope (LAT). Causality arguments constrain the size of the emission region to 1.6 × 1015 cm. The γ-ray spectra measured over this period show clear deviations from a simple power law with a break in the 1-2 GeV energy range. We discuss possible explanations for the origin of the γ-ray spectral breaks. Our study suggests that the γ-ray emission region in 3C 273 is located within the broad line region (< 1.6 pc). The spectral behavior and temporal characteristics of the individual flares indicate the presence of multiple shock scenarios at the base of the jet.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- September 2013
- DOI:
- 10.1051/0004-6361/201321440
- arXiv:
- arXiv:1307.0854
- Bibcode:
- 2013A&A...557A..71R
- Keywords:
-
- gamma rays: galaxies;
- galaxies: active;
- quasars: individual: 3C 273;
- Astrophysics - High Energy Astrophysical Phenomena;
- Astrophysics - Cosmology and Nongalactic Astrophysics
- E-Print:
- 11 pages, 8 figures, accepted for publication in A&