73 research outputs found
Gamma-Ray Emision from the Broad-Line Radio Galaxy 3C 111
The broad-line radio galaxy 3C 111 has been suggested as the counterpart of the Gamma-ray source 3EGJ0416+3650. While 3C 111 meets most of the criteria for a high-probability identification, like a bright fla t-spectrum radio core and a blazarlike broadband SED, in the Third EG RET Catalog, the large positional offset of about 1.5 degrees put 3C1 11 outside the 99% probability region for 3EG J0416+3650, making this association questionable. We present a re-analysis of all available data for 3C111 from the EGRET archives, resulting in probable detection of high-energy Gamma-ray emission above 1000MeV from a position clo se to the nominal position of 3C 111, in two separate viewing periods (VPs), at a 3sigma level in each. A new source, GROJ0426+3747, appea rs to be present nearby, seen only in the >1000MeV data. For >100MeV, the data are in agreement with only one source (at the original cata log position) accounting for most of the EGRET-detected emission of 3 EGJ0416+3650. A follow-up Swift UVOT/XRT observation reveals one mode rately bright X-ray source in the error box of 3EGJ0416+3650, but bec ause of the large EGRET position uncertainty, it is not certain that the X-ray and Gamma-ray sources are associated. A Swift observation of GROJ0426+3747 detected no X.ray source nearby
High Resolution Rapid Response observations of compact radio sources with the Ceduna Hobart Interferometer (CHI)
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.Comment: 6 pages, 6 figures, 1 table. Accepted for publication in A&
Twelve and a Half Years of Observations of Centaurus A with RXTE
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.Comment: 56 pages, 12 figures, 4 tables, revised manuscript submitted to The
Astrophysical Journa
X-ray monitoring of the radio and gamma-ray loud Narrow-Line Seyfert 1 Galaxy PKS 2004-447
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.Comment: Proceedings for the 'Jet 2013' conference. Includes 3 pages, 3
figure
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