Journal
ASTROPHYSICAL JOURNAL LETTERS
Volume 758, Issue 1, Pages -Publisher
IOP PUBLISHING LTD
DOI: 10.1088/2041-8205/758/1/L15
Keywords
galaxies: active; gamma rays: galaxies; quasars: general; radiation mechanisms: non-thermal
Categories
Funding
- NASA ATFP [NNX08AG77G]
- Fermi grant [NNX12AF01G]
- LTSA [NNX07AM17G]
- NASA [NNX08AG77G, 98152] Funding Source: Federal RePORTER
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The distance of a Fermi-detected blazar gamma-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 gamma-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 gamma-ray emission to be almost achromatic. If, on the other hand, the gamma-ray emission is produced farther out in the parsec-scale MT, the IC scattering of the infrared (IR) MT seed photons that produces the gamma-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.
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