期刊
ASTRONOMY & ASTROPHYSICS
卷 515, 期 -, 页码 -出版社
EDP SCIENCES S A
DOI: 10.1051/0004-6361/200913915
关键词
radio continuum: galaxies; techniques: high angular resolution; techniques: interferometric; galaxies: active; galaxies: jets
资金
- EU [MEST/CT/2005/19669]
- Russian Foundation for Basic Research [08-02-00545]
- Alexander von Humboldt
- National Science Foundation [AST-0807860]
- NASA [NNX08AV67G]
Context. A bright feature 80 pc away from the core in the powerful jet of M87 shows highly unusual properties. Earlier radio, optical, and X-ray observations have shown that this feature, labeled HST-1, is superluminal, and is possibly connected with the TeV flare detected by HESS in 2005. It has been claimed that this feature might have a blazar nature because of these properties. Aims. To examine whether HST-1 has a blazar-like nature, we analyzed lambda 2 cm VLBA archival data from dedicated full-track observations and the 2 cm survey/MOJAVE VLBI monitoring programs performed between 2000 and 2009. Methods. We studied the subparsec scale structure of M 87 jet by using wide-field imaging techniques, after checking different weighting of the interferometric visibilities as a function of distance. The HST-1 region was imaged at milliarcsecond resolution. Results. We present the first 2 cm VLBI detection of HST-1 in observations performed between early 2003 and early 2007, and analyze its evolution with time. Using the detections of HST-1, we find that the projected apparent speed is 0.61 +/- 0.31c. A comparison of the VLA and VLBA flux densities of this feature indicates that it is mostly resolved on milliarcsecond scales. This feature is optically thin (alpha similar to -0.8 for S proportional to nu(+alpha)) between lambda 2 cm and lambda 20 cm. Conclusions. We do not find evidence that HST-1 has a blazar nature.
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