Understanding the spectrum of a distant blazar PKS 1424 + 240 and its implications
We calculate the gamma-ray spectrum of a distant blazar, PKS 1424 + 240, located at redshift z ⩾ 0.6035, where the optical depth to primary gamma rays of the highest observed energies is τ ⩾ 5. The spectral shape agrees well with what is expected from secondary gamma rays produced in line-of-sight interactions of cosmic rays with background photons. In particular, we find an acceptable agreement with the source redshifts in the range 0.6 ⩽ z ⩽ 1.3. We discuss the implications of existing and future data for models of extragalactic background light (EBL) and for the redshift of the source. In the case of a future detection of temporal variability at lower energies, one can set more restrictive limits on both the source redshift and the EBL spectrum.
- Pub Date:
- May 2014
- Astrophysics - High Energy Astrophysical Phenomena
- 8 pages, 3 figures