oalib

Publish in OALib Journal

ISSN: 2333-9721

APC: Only $99

Submit

Search Results: 1 - 10 of 6190 matches for " Matthias Kadler "
All listed articles are free for downloading (OA Articles)
Page 1 /6190
Display every page Item
Extragalactic Jets from the TANAMI Sample as Seen by Fermi/LAT
Moritz Boeck,Matthias Kadler,Gino Tosti,Toby Burnett,Roopesh Ojha,Cornelia Mueller,Joern Wilms
Physics , 2009,
Abstract: The TANAMI program has been monitoring the parsec-scale radio jets of southern gamma-ray bright AGN with VLBI techniques simultaneously with Fermi/LAT monitoring of their gamma-ray emission. Here we present the gamma-ray properties of the TANAMI sources based on an analysis of the preliminary 1-year LAT source list. We present upper limits on the gamma-ray flux for TANAMI sources not detected by LAT.
The TANAMI Program
Roopesh Ojha,Matthias Kadler,Moritz Boeck,Faith Hungwe,Cornelia Mueller,Joern Wilms,Eduardo Ros,the TANAMI Team
Physics , 2010,
Abstract: The TANAMI (Tracking AGN with Austral Milliarcsecond Interferometry) program provides comprehensive VLBI monitoring of extragalactic gamma-ray sources south of declination -30 degrees. Operating at two radio frequencies (8 and 22 GHz), this program is a critical component of the joint quasi-simultaneous observations with the Fermi Gamma-ray Space Telescope and ground based observatories to discriminate between competing theoretical blazar emission models. We describe the TANAMI program and present early results on the 75 sources currently being monitored.
The blazar-like radio structure of the TeV source IC310
Matthias Kadler,Dorit Eisenacher,Eduardo Ros,Karl Mannheim,Dominik Els?sser,Uwe Bach
Physics , 2012, DOI: 10.1051/0004-6361/201118212
Abstract: Context. The radio galaxy IC310 in the Perseus cluster has recently been detected in the gamma-ray regime at GeV and TeV energies. The TeV emission shows time variability and an extraordinarily hard spectrum, even harder than the spectrum of the similar nearby gamma-ray emitting radio galaxy M87. Aims. High-resolution studies of the radio morphology help to constrain the geometry of the jet on sub-pc scales and to find out where the high-energy emission might come from. Methods. We analyzed May 2011 VLBA data of IC310 at a wavelength of 3.6 cm, revealing the parsec-scale radio structure of this source. We compared our findings with more information available from contemporary single-dish flux density measurements with the 100-m Effelsberg radio telescope. Results. We have detected a one-sided core-jet structure with blazar-like, beamed radio emission oriented along the same position angle as the kiloparsec scale radio structure observed in the past by connected interferometers. Doppler-boosting favoritism is consistent with an angle of theta < 38 degrees between the jet axis and the line-of-sight, i.e., very likely within the boundary dividing low-luminosity radio galaxies and BL Lac objects in unified schemes. Conclusions. The stability of the jet orientation from parsec to kiloparsec scales in IC310 argues against its classification as a headtail radio galaxy; i.e., there is no indication of an interaction with the intracluster medium that would determine the direction of the tail. IC310 seems to represent a low-luminosity FRI radio galaxy at a borderline angle to reveal its BL Lac-type central engine.
Twelve and a Half Years of Observations of Centaurus A with RXTE
Richard E. Rothschild,Alex Markowitz,Elizabeth Rivers,Slawomir Suchy,Katja Pottschmidt,Matthias Kadler,Cornelia Mueller,Joern Wilms
Physics , 2011, DOI: 10.1088/0004-637X/733/1/23
Abstract: The Rossi X-ray Timing Explorer has observed the nearest radio galaxy, Centaurus A, in 13 intervals from 1966 August to 2009 February over the 3--200 keV band. Spectra accumulated over the 13 intervals were well described with an absorbed power law and iron line. Cut-off power laws and Compton reflection from cold matter did not provide a better description. For the 2009 January observation, we set a lower limit on the cut-off energy at over 2 MeV. The power spectral density function was generated from RXTE/ASM and PCA data, as well as an XMM-Newton long look, and clear evidence for a break at 18+10-7 days (68% conf.) was seen. Given Cen A's high black hole mass and very low value of Lx/LEdd, the break was a factor of 17+/-9 times higher than the break frequency predicted by the McHardy and co-workers' relation, which was empirically derived for a sample of objects, which are radio-quiet and accreting at relatively high values of Lbol/LEdd. We have interpreted our observations in the context of a clumpy molecular torus. The variability characteristics and the broadband spectral energy distribution, when compared to Seyferts, imply that the bright hard X-ray continuum emission may originate at the base of the jet, yet from behind the absorbing line of sight material, in contrast to what is commonly observed from blazars.
X-ray Variability Study of Polar Scattered Seyfert 1 Galaxies
Tobias Beuchert,J?rn Wilms,Matthias Kadler,Anna Lia Longinotti,Matteo Guainazzi,Giovanni Miniutti,Ignacio de la Calle
Physics , 2013,
Abstract: We study 12 Seyfert 1 galaxies with a high level of optical polarization. Optical light emerging from the innermost regions is predominantly scattered in a polar region above the central engine directly in our line of sight. These sources show characteristics of Seyfert 2 galaxies such as, e.g., polarized broad lines. The polarization signatures suggest a viewing angle of 45 degrees classifying them as intermediate Seyfert 1/2 types. The unified model predicts this line of sight to pass through the outer layer of the torus resulting in significant soft X-ray variability due to a strongly varying column density. The aim is to find evidence for this geometrical assumption in the spectral variability of all available historical observations of these sources by XMM-Newton and Swift.
VLBI Monitoring of the bright gamma-ray blazar PKS 0537-441
Faith Hungwe,Roopesh Ojha,Matthias Kadler,Roy Booth,Jay Blanchard,Jim Lovell,Cornelia Mueller,Moritz Boeck,the TANAMI team
Physics , 2010,
Abstract: One of the defining characteristics of BL Lacertae objects is their strong variability across the electromagnetic spectrum. PKS 0537-441 is one such object and is one of the most luminous blazars from radio to gamma-ray wavelengths. It was detected as a strong and highly variable source by EGRET and has been reported several times to be in an active state by Fermi . It is one of the brightest gamma-ray blazars detected in the southern sky so far. The TANAMI (Tracking Active Galactic Nuclei with Austral Milliarcsecond Interferometry) program is monitoring PKS 0537-441 at VLBI resolutions. We present 8.4 GHz and 22 GHz images of the milliarcsecond scale structure. We also present our ongoing analysis of the spectral and temporal changes in this object.
High Resolution Rapid Response observations of compact radio sources with the Ceduna Hobart Interferometer (CHI)
Jay M. Blanchard,James E. J. Lovell,Roopesh Ojha,Matthias Kadler,John M. Dickey,Philip G. Edwards
Physics , 2012, DOI: 10.1051/0004-6361/201117593
Abstract: Context. Frequent, simultaneous observations across the electromagnetic spectrum are essential to the study of a range of astrophysical phenomena including Active Galactic Nuclei. A key tool of such studies is the ability to observe an object when it flares i.e. exhibits a rapid and significant increase in its flux density. Aims. We describe the specific observational procedures and the calibration techniques that have been developed and tested to create a single baseline radio interferometer that can rapidly observe a flaring object. This is the only facility that is dedicated to rapid high resolution radio observations of an object south of -30 degrees declination. An immediate application is to provide rapid contemporaneous radio coverage of AGN flaring at {\gamma}-ray frequencies detected by the Fermi Gamma-ray Space Telescope. Methods. A single baseline interferometer was formed with radio telescopes in Hobart, Tasmania and Ceduna, South Australia. A software correlator was set up at the University of Tasmania to correlate these data. Results. Measurements of the flux densities of flaring objects can be made using our observing strategy within half an hour of a triggering event. These observations can be calibrated with amplitude errors better than 15%. Lower limits to the brightness temperatures of the sources can also be calculated using CHI.
Multiwavelength observations of TANAMI sources
Felicia Krau?,Cornelia Müller,Matthias Kadler,J?rn Wilms,Moritz B?ck,Roopesh Ojha,Eduardo Ros
Physics , 2013,
Abstract: The TANAMI VLBI program is monitoring a sample of 84 Active Galactic Nuclei of the Southern Sky at 8.4 and 22 GHz. The combination of VLBI and multiwavelength data allows us to study changes in the spectral energy distributions, as well as changes in the structure of the inner jets and to search correlations between both. We present initial results of the multiwavelength analysis of a sub-sample of the TANAMI sources, combining our radio data with simultaneous X-ray and optical/UV observations from Swift and XMM-Newton, and gamma-ray data from Fermi, focusing on the broadband spectral energy distributions as well as variability in different wavebands.
X-ray monitoring of the radio and gamma-ray loud Narrow-Line Seyfert 1 Galaxy PKS 2004-447
Annika Kreikenbohm,Matthias Kadler,J?rn Wilms,Robert Schulz,Cornelia Müller,Roopesh Ojha,Eduardo Ros,Karl Mannheim,Dominik Els?sser
Physics , 2013, DOI: 10.1051/epjconf/20136104017
Abstract: We present preliminary results of the X-ray analysis of XMM-Newton and Swift observations as part of a multi-wavelength monitoring campaign in 2012 of the radio-loud narrow line Seyfert 1 galaxy PKS 2004-447. The source was recently detected in gamma-rays by Fermi/LAT among only four other galaxies of that type. The 0.5-10 keV X-ray spectrum is well-described by a simple absorbed powerlaw (photon index ~ 1.6). The source brightness exhibits variability on timescales of months to years with indications for spectral variability, which follows a 'bluer-when-brighter' behaviour, similar to blazars.
Multi-wavelength Observations of PKS 2142-758 during an Active Gamma-Ray State
Michael Dutka,Roopesh Ojha,Katja Pottschmidt,Justin Finke,Jamie Stevens,Jay Blanchard,Roberto Nesci,Philip Edwards,Jim Lovell,Matthias Kadler,Joern Wilms,Gino Tosti,Tapio Pursimo
Physics , 2012,
Abstract: PKS 2142-758 is a flat spectrum radio quasar which emits few, weak but significant gamma-ray flares in the MeV through GeV energy range. The first flare occured on April 4th, 2010, when the source reached a daily flux of (1.1 \pm 0.3) * 10^-6 ph cm^-2 s^-1 (ATEL #2539) in the 100 MeV to 300 GeV range. This flux represented more than an order of magnitude increase over its quiescent flux. Since the initial flare, this source has been detected in an elevated state within the same energy range from October to November of 2010 and another period ranging from July to August of 2011. During the latest flaring period in 2011 a multi wavelength observing campaign was carried out using the Ceduna radio telescope, the Australian Telescope Compact Array (ATCA), the TANAMI VLBI Array, Swift, the Rapid Eye Mount Telescope (REM), and the Large Area Telescope (LAT) on board Fermi. These quasi-simultaneous data were used to construct a broadband SED of this object in its rare active state. We present these observations and the resulting SED and some preliminary analysis of the constraints they place on the high energy emission from this object.
Page 1 /6190
Display every page Item


Home
Copyright © 2008-2017 Open Access Library. All rights reserved.