An explanation about the flat radio spectrum for Mrk 421
Abstract
It is well known that a flat radio spectrum is a common property in the spectral energy distribution of blazars. Although one-zone leptonic models are generally successful in explaining the multi-wave band emission, they are problematic in reproducing the radio spectrum. In the study of Mrk 421, one-zone models suggest that in order to avoid overproducing the radio flux, the minimum electron Lorentz factor should be larger than a few hundred at least, even considering the synchrotron self-absorption effect. This result suggests that the model predicted spectral index in the radio band of Mrk 421 should be -1/3. On the basis of this result, by assuming there is a neglected region that will also contribute the radio emission and its electron energy index naturally originates from the simplest first-order Fermi acceleration mechanism, we can get a superimposed flat radio spectrum. In this paper, a two-zone model is proposed to reproduce the quiescent state spectral energy distribution of Mrk 421. In addition to taking into account the emission from a conventional radiation zone, we further consider emission from the acceleration zone in which particles are accelerated at a shock front. With the present model, our fitting result suggests that the low frequency flat radio spectrum of Mrk 421 might be explained as a superposition of the synchrotron emission from acceleration zone and radiation zone.
- Publication:
-
Research in Astronomy and Astrophysics
- Pub Date:
- May 2021
- DOI:
- 10.1088/1674-4527/21/4/103
- arXiv:
- arXiv:2011.06439
- Bibcode:
- 2021RAA....21..103X
- Keywords:
-
- galaxies: active;
- galaxies: jets;
- radiation mechanisms: non-thermal;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 9 pages, 3 figures, accepted in RAA