A Search for Tev Emission From X-ray Selected Agn with Milagro

A TeV emission component has been detected from several active galactic nuclei (AGN). The majority of TeV detections of AGN are for nearby (z < 0.13) X-ray selected BL Lacs in flaring states. The variability of these sources makes continuous monitoring necessary to detect flaring activity. The Milagro gamma-ray observatory is a wide-field (∼2 sr) instrument that operates continuously allowing daily observations of the Northern hemisphere. No significant detections of unidentified sources have been made to date. The observations are used to set limits on the time-integrated behavior of a set of X-ray selected BL Lacs. Costamante and Ghisellini [A&A 384 (2002) 56] present a selection of BL Lacs with X-ray and radio flux levels favorable for TeV emission and make predictions for the TeV flux levels. Twenty-seven objects selected from this sample are the subjects of a search for TeV emission on time scales from 8 days to 2.8 years in data taken between December 15, 2000, and September 8, 2003. None of the selected BL Lacs are detected on any of the time scales. Flux limits will be presented for each galaxy and time scale and comparisons will be made with the predicted emission. For the Milagro Collaboration.     

河外水脉泽的研究进展

人们对河外水脉泽的观测与研究已经30年了。目前已经在约70个河外星系中检测到水脉泽辐射（已公开发表64个）。近年来，河外水脉泽的观测及理论研究十分活跃。重点介绍了目前河外水脉泽的检测及研究进展，包括水脉泽源的分类、水脉泽对研究活动星系核的重要科学价值、水脉泽源的X射线观测研究及其各物理量之间的统计分析结果等。     

BVRI CCD-Photometry of Comparison Stars in the Neighborhoods of Galaxies with Active Nuclei. I

Results are presented from CCD BVRI observations of comparison stars in the neighborhoods of 22 galaxies with active nuclei having right ascensions ranging from 0 to 12 hours, of which 19 are Seyfert galaxies. The observed stars have magnitudes ranging from V=11 to V=17. For stars brighter than V=14 the typical photometic error is 0.01^m. The B, V, Rc, and Ic magnitudes of most of these stars were not known previously. 14′×14′ finding charts are included. These results can be used for differential photometry of the AGNs in the B, V, Rc, and Ic bands.__________Translated from Astrofizika, Vol. 48, No. 2, pp. 191–211 (May 2005).     

On the difference between the X-ray selected and the radio selected BL Lac objects in the near infrared

By using results from the 2MASS observation, the differences between the X-ray selected BL Lac objects (XBLs) and the radio selected ones (RBLs) in the near infrared are discussed in this paper. It is found that, statistically, the RBLs have redder near infrared colors and steeper spectral indices in the near infrared than XBLs, whereas the XBLs have more influences from their host galaxies than the RBLs. It is also seen that the RBLs have much brighter luminosity in the near infrared than the XBLs. In addition, the high polarization characteristics are found in common for RBLs, but not for XBLs.     

Multiwavelength observations of blazars: a summary

Because of their broad-band nature, multiwavelength observations of blazars are crucial to constrain the emission mechanisms, structure, and physical quantities of the inner jet on parsec and sub-parsec scales. Here I briefly review selected multiwavelength observations of blazars with a particular emphasis on sources detected at GeV and TeV gamma-rays. Their properties are discussed in the frame of the blazar “luminosity sequence”.     

AGN effect on cooling flow dynamics

We analyzed the feedback of AGN jets on cooling flow clusters using three-dimensional AMR hydrodynamic simulations. We studied the interaction of the jet with the intracluster medium and creation of low X-ray emission cavities (Bubbles) in cluster plasma. The distribution of energy input by the jet into the system was quantified in its different forms, i.e. internal, kinetic and potential. We find that the energy associated with the bubbles, (pV+γ pV/(γ−1)), accounts for less than 10 percent of the jet energy.     

Blazar短时标光变的孔径测光分析

对IRAF软件包处理AGN观测数据中,测光孔径、背景环的内外径差、背景等参数选取对测光结果的影响进行了实测比较.结果表明孔径的选取对测光结果的影响较大,而背景环的内外径差参数的影响不大;对所处理的观测序列中,背景参数对测光结果没有影响.对Blazar短时标光变监测中由于比较星选择引起的修正因子Γ进行了讨论,并对在2007年3月观测的PKS1510-089和OJ248数据进行了计算和比较分析.     

On the difference in short timescale light variation between the high and low states of BL Lac objects

Combining our data for three BL Lac objects obtained in 1993–1995 with other authors' we note that activity is stronger and short timescale variations more frequent during the high than the low state. We propose that the relativistic jet in the AGN may change its orientation with time, and the high state corresponds to smaller angles of inclination to the line of sight, and the low, to larger angles. This explains the difference in behaviour as well as the new phenomenon discovered in the monitoring by Takalo et al.     

Results of VLBI monitoring of 3C273 at 22 GHz and 43 GHz

The results of VLBI observations of the quasar 3C273, obtained during a multi-band campaign, are presented. The changes in separation from the core of the components along the first 2 mas of the jet were measured. The jet starts wiggling well inside the first parsec from the core. We derived the period of the oscillating jet path around the principal jet-axis in the range 2–8 mas from the core. The components' angular sizes, their peak fluxes, and turnover frequencies were also derived from the VLBI observations. We have derived lower limits to the Doppler factor by comparing the observed X-ray fluxes with those predicted by the synchrotron self-Compton model. Independent estimates were obtained through the assumption of energy equipartition between particles and magnetic field.