相关论文: High Observed Brightnesses in Radio Jets
We present a new method to measure Gamma*theta_j in flux-limited samples of active galactic nuclei (AGN) jets, where Gamma is the bulk Lorentz factor and theta_j is the jet's half-opening angle. The Gamma*theta_j parameter is physically…
Rapid variability on a time scale much faster than the light-crossing time of the central supermassive black hole has been seen in TeV emission from the blazar PKS 2155-304. The most plausible explanation of this puzzling observation is…
Both induced Compton scattering and induced Raman scattering strongly limit the observability of the extremely bright (<< 10^21K), prompt coherent radio emission recently predicted to emanate from gamma-ray bursts. Induced Compton…
Radio galaxies are episodic in nature. In our recent work, our study of jet properties and their dynamics in different episodes of activity has revealed various hitherto unknown aspects of the extragalactic jets. We discover that the…
Using newly released data from the Wide-field Infrared Survey Explorer, we report the discovery of rapid infrared variability in three radio-loud narrow-line Seyfert 1 galaxies (NLS1s) selected from the 23 sources in the sample of Yuan et…
Active galactic nuclei come in many varieties. A minority of them are radio-loud, and exhibit two opposite prominent plasma jets extending from the proximity of the supermassive black hole up to megaparsec distances. When one of the…
In extragalactic jets, the apparent position of the bright/narrow end (the core) depends on the observing frequency, owing to synchrotron self-absorption and external absorption. The effect must be taken into account in order to achieve…
We present a study of variability time scales in a large sample of Active Galactic Nuclei at several frequencies between 4.8 and 230 GHz. We investigate the differences of various AGN types and frequencies and correlate the measured time…
The intrinsic luminosity functions of extremely fast jets found in many active galaxies and gamma-ray bursts are difficult to measure since their apparent luminosities are strongly affected by relativistic beaming. Past studies have only…
We have carried out numerical hydrodynamic simulations of radio jets from active galactic nuclei using the PLUTO simulation code, with the aim of investigating the effect of different environments and intermittency of energy injection on…
The rapid time variability of gamma-ray bursts implies the sources are very compact, and the peak luminosities are so high that some matter must be ejected at ultra-relativistic speeds. The very large Lorentz factors of the bulk flow are…
Among active galactic nuclei, blazars show extreme variability properties. We here investigate the case of the BL Lac object S4 0954+65 with data acquired in 2019-2020 by the Transiting Exoplanet Survey Satellite (TESS) and by the Whole…
It is generally believed that the variability of photospheric emission in gamma-ray bursts (GRBs) traces that of the jet power. This work further investigates the variability of photospheric emission in a variable jet. By setting a constant…
Gamma-ray bursts (GRBs) are powered by relativistic jets that exhibit intermittency over a broad range of timescales - from $ \sim $ ms to seconds. Previous numerical studies have shown that hydrodynamic (i.e., unmagnetized) jets that are…
We discuss physical constrains that observations of high brightness temperature coherent radio emission, with brightness temperatures as high as $T_b \sim 10^{35}$ K, impose on the plasma parameters at relativistically moving astrophysical…
We summarize results from flux density monitoring campaigns performed with the 100 meter radio-telescope at Effelsberg and the VLA during the past 15 yrs. We briefly discuss some of the statistical properties of the rapid variability from…
Observational studies of GHz peaked spectrum (GPS) sources contribute to the understanding of the radiative properties and interstellar environment of host galaxies. We present the results from the multi-frequency high-resolution VLBI…
Tidal disruption events (TDEs) are transient, multi-wavelength events in which a star is ripped apart by a supermassive black hole. Observations show that in a small fraction of TDEs, a short-lived, synchrotron emitting jet is produced. We…
We present a new method how to discriminate the matter content of parsec-scale jets of active galactic nuclei. By constraining the kinetic luminosity of a jet from the observed core size at a single very long baseline interferometry…
The fine-scale structure and the kinematics of relativistic active galactic nuclei (AGN) jets have been studied by very-long-baseline interferometry at very high resolutions since 1998 at 2 cm wavelength for a sample of over a hundred radio…