Zhao-Qiang Shen

Simultaneous multiwavelength observations of sagittarius A

We observed Sgr A* using the Very Large Array (VLA) and the Giant Metrewave Radio Telescope (GMRT) at multiple centimeter and millimeter wavelengths on 2003 June 17. The measured flux densities of Sgr A*, together with those obtained from the Submillimeter Array (SMA) and the Keck II 10 m telescope on the same date, are used to construct a simultaneous spectrum of Sgr A* from 90 cm to 3.8 mu m. The simultaneous spectrum shows a spectral break at about 3.6 cm, a possible signature of synchrotron self-absorption of the strong radio outburst that occurred near epoch 2003 July 17. At 90 cm, the flux density of Sgr A* is 0.22 +/- 0.06 Jy, suggesting a sharp decrease in flux density at wavelengths longer than 47 cm. The spectrum at long cm wavelengths appears to be consistent with free-free absorption by a screen of ionized gas with a cutoff similar to 100 cm. This cutoff wavelength appears to be three times longer than that of similar to 30 cm suggested by Davies, Walsh, & Booth based on observations in 1974 and 1975. Our analysis suggests that the flux densities of Sgr A* at wavelengths longer than 30 cm could be attenuated and modulated by stellar winds from massive stars close to Sgr A*.

Search for gamma-ray emission from eight dwarf spheroidal galaxy candidates discovered in Year Two of Dark Energy Survey with Fermi-LAT data

Very recently the Dark Energy Survey (DES) Collaboration has released their second group of Dwarf spheroidal (dSph) galaxy candidates. With the publicly-available Pass 8 data of Fermi-LAT we search for

Search for a gamma-ray line feature from a group of nearby Galaxy clusters with Fermi LAT Pass 8 data

\gamma-

‘Excess’ of primary cosmic ray electrons

ray emissions from the directions of these eight newly discovered dSph galaxy candidates. No statistically significant

Multi-epoch VLBA observations of 3C 66A

\gamma-

Superluminal motion in a compact steep spectrum radio source 3C 138

ray signal has been found in the combined analysis of these sources. With the empirically estimated J-factors of these sources, the constraint on the annihilation channel of

The core-like nature of HST-1 in the M87 jet

\chi\chi \rightarrow \tau^{+}\tau^{-}

Multiwaveband polarimetric observations of NRAO 530 on parsec-scale

is comparable to the bound set by the joint analysis of fifteen previously known dSphs with kinematically constrained J-factors for the dark matter mass

The center of activity in the compact steep-spectrum superluminal source 3C 138

m_\chi>250

The parsec-scale jet of PKS 1749+096

GeV. In the direction of Tucana III (DES J2356-5935), one of the nearest dSph galaxy candidates that is