A Method for Localizing Energy Dissipation in Blazars Using Fermi Variability
Abstract
The distance of a Fermi-detected blazar γ-ray emission site from a supermassive black hole is a matter of active debate. Here we present a method for testing if the GeV emission of powerful blazars is produced within the subparsec-scale broad-line region (BLR) or farther out in the parsec-scale molecular torus (MT) environment. If the GeV emission takes place within the BLR, the inverse Compton (IC) scattering of the BLR ultraviolet (UV) seed photons that produces the γ-rays takes place at the onset of the Klein-Nishina regime. This causes the electron cooling time to become practically energy-independent and the variation of the γ-ray emission to be almost achromatic. If, on the other hand, the γ-ray emission is produced farther out in the parsec-scale MT, the IC scattering of the infrared (IR) MT seed photons that produces the γ-rays takes place in the Thomson regime, resulting in energy-dependent electron cooling times, manifested as faster cooling times for higher Fermi energies. We demonstrate these characteristics and discuss the applicability and limitations of our method.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- October 2012
- DOI:
- 10.1088/2041-8205/758/1/L15
- arXiv:
- arXiv:1209.2053
- Bibcode:
- 2012ApJ...758L..15D
- Keywords:
-
- galaxies: active;
- gamma rays: galaxies;
- quasars: general;
- radiation mechanisms: non-thermal;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- Accepted by Astrophysical Journal Letters