排序方式: 共有54条查询结果,搜索用时 46 毫秒
31.
Elizabeth Hays 《Astrophysics and Space Science》2005,297(1-4):43-52
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. 相似文献
32.
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。 相似文献
33.
V. T. Doroshenko S. G. Sergeev N. I. Merkulova E. A. Sergeeva Yu V. Golubinsky V. I. Pronik N. N. Okhmat 《Astrophysics》2005,48(2):156-178
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 0.01m. 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). 相似文献
34.
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. 相似文献
35.
Rita M. Sambruna 《Astrophysics and Space Science》2007,311(1-3):241-246
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”. 相似文献
36.
Fathallah Alouani Bibi James Binney Katherine Blundell Henrik Omma 《Astrophysics and Space Science》2007,311(1-3):317-321
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. 相似文献
37.
38.
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. 相似文献
39.
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. 相似文献
40.