相关论文: PKS 0405--385: the smallest radio quasar?
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…
We report on the discovery of a source which exhibits over 300% amplitude changes in radio flux density on the period of hours. This source, J1819+3845, is the most extremely variable extragalactic source known in the radio sky. We believe…
The remarkable rapid variations in radio flux density and polarization of the quasar PKS 0405-385 observed in 1996 are subject to a correlation analysis, from which characteristic time scales and amplitudes are derived. The variations are…
We show that an upper limit of ~ 10^{12} K on the peak brightness temperature for an incoherent synchrotron radio source, commonly referred to in the literature as an inverse Compton limit, may not really be due to inverse Compton effects.…
The occurrence of the inverse Compton catastrophe when the synchrotron brightness temperature exceeds a threshold value, usually estimated to be 10^{12} K, appears to be in contradiction with observation because: (i) the threshold is…
We discuss here a limit on the maximum brightness temperature achievable for an incoherent synchrotron radio source. This limit, commonly referred to in the literature as an inverse Compton limit, prescribes that the brightness temperature…
Some rapidly variable extra-galactic radio sources show very high brightness temperatures T_B>10^{12}K and high degrees of circular polarisation (1%). Standard synchrotron models that assume a power-law electron distribution cannot produce…
The observed variability of BL Lac objects and Quasars on timescales <1 day (intraday variability, IDV) have revealed radio brightness temperatures up to 10^{16}-10^{20} K. These values challenge the beaming model with isotropic comoving…
We review the observations of rapid flux density variations in compact radio sources, and discuss the inverse Compton limit to the maximum brightness temperature of incoherent synchrotron sources in comparison with recent VLBA observations.…
We report the discovery of fast, frequency-dependent intensity variations from the scintillating intra-day variable quasar J1819+3845 at a wavelength of 21cm which resemble diffractive interstellar scintillations observed in pulsars. The…
The BL Lac object S5 0716+71 was observed in a global multi-frequency campaign to search for rapid and correlated flux density variability and signatures of an inverse-Compton (IC) catastrophe during the states of extreme apparent…
PKS\,1351$-$018 at a redshift of $z=3.71$ is one of the most luminous, steady synchrotron sources with a luminosity $> 10^{47}$\,erg~s$^{-1}$. The synchrotron luminosity does not seem to vary by more than $\sim 25\%$ over 35 years. In order…
We investigate the relation between the Doppler factor determined from variations in total flux at 22 and 37 GHz, and the apparent transverse velocity determined from VLBA observations at 2 cm. The data are consistent with the relativistic…
We present results from several XMM-Newton observations of the radio loud Narrow-line Seyfert 1 galaxy (NLS1) PKS 0558-504. We find evidence for strong and persistent X-ray variability, both on short and long time-scales. On short time…
Some intra-day variable, compact extra-galactic radio sources show brightness temperatures severely exceeding 10^{12} K, the limit set by catastrophic inverse-Compton (IC) cooling in sources of incoherent synchrotron radiation. The…
Comparing the asymmetry coefficients and scintillation indices for observed time variations of the intensity of the radiation of extragalactic sources and the predictions of theoretical models is a good test of the nature of the observed…
We report on the detection of a feature with negative radio flux in a sensitive, low resolution observation with the VLA. This morphologically peculiar feature is approximately 25" 65" in size with a peak central amplitude of about -0.25 mK…
We present new X-ray (Chandra) and radio (ATCA) observations of the z=0.09 radio galaxy PKS B1416-493, a member of the southern equivalent of the 3CRR sample. We find the source to be embedded in a previously unrecognized bright kT=4.6 keV…
We report the discovery of an intervening 21\,cm absorption line at z = 0.882 towards the z = 1.284 quasar PKS 0405-385, identified in the First Large Absorption Survey in HI (FLASH). This quasar once displayed the most rapid known intraday…
From 1979--1996 the Green Bank Interferometer was used by the Naval Research Laboratory to monitor the flux density from 146 compact radio sources at frequencies near 2 and 8 GHz. We filter the ``light curves'' to separate intrinsic…