arXiv subjects

C. S. Chang

Publications and source records attributed to C. S. Chang.

41 records · Page 3Linked to original sources

arXiv2010

VLBI detection of the HST-1 feature in the M87 jet at 2 cm

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, due to these properties. To examine the possible blazar-like nature of HST-1, we analyzed lambda 2 cm VLBA archival data from dedicated full-track observations and the 2 cm survey/MOJAVE VLBI monitoring programs obtained between 2000 and 2009. Applying VLBI wide-field imaging techniques, the HST-1 region was imaged at milliarcsecond resolution. Here we present the first 2 cm VLBI detection of this feature in observations from early 2003 to early 2007, and analyze its evolution over this time. Using the detections of HST-1, we find that the projected apparent speed is 0.61 +/- 0.31 c. A comparison of the VLA and VLBA flux densities of this feature indicate that is mostly resolved on molliarcsecond scales. This feature is optically thin between lambda 2 cm and lambda 20 cm. We do not find evidence of a blazar nature for HST-1.

astro-ph.CO↗

arXiv2010

Multiwavelength campaign of the gamma-ray flaring source PKS 2052-47

The flat-spectrum radio quasar PKS 2052-47 experienced an optical flare in July-August, 2009. On August 9, the LAT detector onboard Fermi observed a flare from the source, which reached its active phase in the following two months. To further investigate the physics and emission mechanisms during the flaring state of this source, we arranged a multiwavelength campaign from radio to gamma-ray to study its spectral energy distribution (SED) and its brightness variations across the spectrum. Here we present the first results of this multiwavelength campaign.

astro-ph.CO↗

arXiv2010

The spectral energy distribution of gamma-faint compact radio sources

MOJAVE is a VLBI program which monitors a statistically complete, radio-selected sample of 135 relativistically beamed, flat-spectrum active galactic nuclei for over more than a decade. In order to understand the high-energy behavior of this radio complete sample, we are performing Swift fill-in observations on the complete MOJAVE-I sample since 2007. The complete study of the spectral energy distribution from radio to X-ray bands on this radio-selected sample will provide us an opportunity to understand the nature of AGN. Here we present the preliminary results of the spectral energy distributions of six gamma-quiet or faint sources from this project: NRAO 140, PKS 0403-13, PKS B0422+004, PKS 0823+033, 3C 309.1, and 3C 380.

astro-ph.CO↗

arXiv2009

A closer look at the flaring feature in the M87 jet

The radio-loud active galactic nucleus in M 87 hosts a powerful jet fueled by a super-massive black hole in its center. A bright feature 80 pc away from the M 87 core has been reported to show superluminal motions, and possibly to be connected with a TeV flare observed around 2005. To complement these studies and to understand the nature of this feature, we analyzed 2 cm VLBI data from 15 observing runs between 2000 and 2009. This feature is successfully detected at the milli-Jansky level from 2003 to 2007. Our detections show that its milli-arcsecond structure appears to be extended with a steep spectrum, and no compact or rapidly moving features are observed. Our results do not favor a blazar scenario for this feature.

astro-ph.CO↗

arXiv2008

15 GHz VLBI detection of the HST-1 feature in the M87 jet

A bright feature 100 pc away from the core in the powerful jet of M 87 shows mysterious properties. Earlier radio, optical and X-ray observations have shown that this feature, labelled HST-1, is superluminal, and is possibly connected with the TeV flare detected by HESS in 2005. To examine the possible blazar-like nature of HST-1, we analyzed 2 cm VLBA data from dedicated full-track observations and the 2 cm survey/MOJAVE VLBI monitoring programs observed from 2000 to 2008. Applying wide-field imaging techniques, the HST-1 region was imaged at milliarcsecond resolutions. Here we present the first 15 GHz VLBI detection of this feature and discuss the connection between our radio findings and the TeV detection.

astro-ph↗