The brightness temperature problem in extreme IDV quasars: a model for PKS 0405-385

Abstract

I re-examine the brightness temperature problem in PKS 0405-385 which is an extreme intra-day variable radio quasar with an inferred brightness temperature of $\sim 5\times 10^{14}$ K at 5 GHz, well above the Compton catastrophe limit of $\sim 10^{11}$ K reached when the synchrotron photon energy density exceeds the energy density of the magnetic field. If one takes into account the uncertainty in the distance to the ionized clouds responsible for interstellar scintillation causing rapid intra-day variability in PKS 0405-385 it is possible that the brightness temperature could be as low as $\sim 10^{13}$ K at 5 GHz, or even lower. The radio spectrum can be fitted by optically thin emission from mono-energetic electrons, or an electron spectrum with a low-energy cut-off such that the critical frequency of the lowest energy electrons is above the radio frequencies of interest. If one observes optically thin emission along a long narrow emission region, the average energy density in the emission region can be many orders of magnitude lower than calculated from the observed intensity if one assumed a spherical emission region. I discuss the physical conditions in the emission region and find that the Compton catastrophe can then be avoided using a reasonable Doppler factor. I also show that MeV to 100 GeV gamma-ray emission at observable flux levels should be expected from extreme intra-day variable sources such as PKS 0405-385.

arXiv comment10 pages, 6 figures. Accepted for publication in MNRAS

References in corpus (8)

• The discovery of a microarcsecond quasar: J1819+3845
• PKS 0405--385: the smallest radio quasar?
• Interstellar scintillation as the origin of rapid radio variability in the quasar J1819+3845
• The ATCA Intraday Variability Survey of Extragalactic Radio Sources
• Design Study of CANGAROO-III, Stereoscopic Imaging Atmospheric Cherenkov Telescopes for sub-TeV Gamma-ray
• Intraday Variability in Northern Hemisphere Radio Sources
• Factors Determining Variability Time in Active Galactic Nucleus Jets
• A very rapid Extreme Scattering Event in the IDV source 0954+658

Cited by in corpus (3)

• Quasi-periodic behaviour in the $\gamma$-ray light curve of the blazar PKS 0405-385
• The inverse Compton catastrophe and high brightness temperature radio sources
• High brightness temperatures and circular polarisation in extra-galactic radio sources