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Short time-scale flux density variations of flat spectrum radio sources are often explained by the scattering of radio waves in the turbulent, ionized Interstellar Matter of the Milky Way. One of the most convincing observational arguments…

Fifteen ROSAT PSPC observations available in the public archive are analyzed in order to study time and spectral variability of the 12 EMSS AGN detected by ROSAT with more than 2000 net counts. Time variability was investigated on 13…

We develop the theory of interstellar scintillation as caused by an irregular plasma having a power-law spatial density spectrum with a spectral exponent of 4 corresponding to a medium with abrupt changes in its density. An ``outer scale''…

Variability of radio-emitting active galactic nuclei can be used to probe both intrinsic variations arising from shocks, flares, and other changes in emission from regions surrounding the central supermassive black hole, as well as…

Variability in the brightness of Young Stellar Objects (YSOs) is a common phenomenon that can be caused by changes in various factors, including accretion, extinction, disk morphology, interactions between the disk and the stellar…

We present observations of the 22 GHz water vapor megamasers in the Circinus galaxy made with the Tidbinbilla 70m telescope. These observations confirm the rapid variability seen earlier by Greenhill et al (1997). We show that this rapid…

As one of targets of many flux monitoring campaigns, the FSRQ 0507+179 shows various flux variation properties at almost all observing wavelengths, from radio to $\gamma$-ray. With Urumqi 25-m telescope, our study on this object is focusing…

We present flux-ratio curves of the fold and cusp (i.e. close multiple) images of six JVAS/CLASS gravitational lens systems. The data were obtained over a period of 8.5 months in 2001 with the Multi-Element Radio-Linked Interferometer…

A small subset of young stellar objects (YSOs) exhibit "see-saw" temporal variations in their mid-infrared SED; as the flux short-ward of a fulcrum wavelength ($\lambda_{f}$) increases the flux long-wards of this wavelength decreases (and…

Very recently, J 1128+5925 was found to show strong intraday variability at radio wavelengths and may be a new source with annual modulation of the timescale of its radio variability. Therefore, its radio variability can be best explained…

Large scale X-ray jets that extend to >100 kpc distances from the host galaxy indicate the importance of jets interactions with the environment on many different physical scales. Morphology of X-ray clusters indicate that the radio-jet…

We report the results of a diffraction-limited, photometric variability study of the central 5"x5" of the Galaxy conducted over the past 10 years using speckle imaging techniques on the W. M. Keck I 10 m telescope. Within our limiting…

This study aims to search for the existence of intraday variability (IDV) of BL Lac object S5 0716+714 at high radio frequencies for which the interstellar scintillation effect is not significant. Using the 21-meter radio telescope of the…

Compact radio sources exhibit scintillation, an interference pattern arising from propagation through inhomogeneous plasma, where scintillation patterns encode the relative distances and velocities of the source, scattering material, and…

We present an analysis of interplanetary scintillation (IPS) observations conducted with the Arecibo 305-m radio telescope during the minimum phase at the end of solar cycle 24 and the onset of solar cycle 25. These observations span a…

Infrared variability is common among young stellar objects, with surveys finding daily to weekly fluctuations of a few tenths of a magnitude. Space-based observations can produce highly sampled infrared light curves, but are often limited…

We describe extensive synoptic multi-wavelength observations of the transition disk LRLL 31 in the young cluster IC 348. We combined four epochs of IRS spectra, nine epochs of MIPS photometry, seven epochs of cold-mission IRAC photometry…

Using the Urumqi 25m radio telescope, sources from the first three-month Fermi-LAT detected AGN catalog with declination >0 were observed in 2009 at 4.8 GHz. The radio flux density appears to correlate with the gamma-ray intensity.…

The BL Lac object S5 0716+71 was target of a coordinated and global multi-frequency campaign to search for rapid and correlated variability and signatures of the inverse-Compton catastrophe. Here we present first results obtained from a…

The processes governing protostellar mass growth remain debated, although episodic accretion is now understood as a key feature of protostellar evolution across all masses. Luminosity bursts have been observed in both low- and high-mass…