621 research outputs found
Jet-Intracluster Medium Interactions of the Head Tail Radio Galaxy 3C 129
The 50 ksec XMM observations of the galaxy cluster 3C 129 were taken as scheduled, and the data are of good quality. We analyzed the data in the following way. After standard cleaning, we flat-fielded the XMM surface brightness maps. Combining the data from the EPIC MOS and PN Camera CCDs, we performed a cross-correlation analysis of the X-ray surface brightness distribution with the 1.4 GHz VLA radio map. We found evidence for cavities in the X-ray emitting Intra-Cluster Medium (ICM) associated with the radio tail of the head-tail radio galaxy 3C 129. This discovery is very interesting as it excludes the presence of a large fraction of thermal plasma in the radio tail. Together with the observation of an apparent pressure mismatch between the radio plasma and the ICM, and an upper limit on the magnetic field inside the radio tail (from the radio spectral indices map) the observation implies that the tail pressure is dominated either by low-energy electrons/positrons, or, by relativistic protons. Furthermore, we studied the energy spectrum of an X-ray "hot-spot" associated with the head of the radio galaxy 3C 129. It seems likely that the X-ray hot-spot originates from shocked gas in front of the radio galaxy. , The analysis turned out to be much more difficult than anticipated. The main reason is the lack of a comprehensive, publicly available background model that is key for the analysis of extended sources. Small groups like our do not have the man-power to come up with a background model themselves. We used the model from Read & Ponman (A&A 409, 395, 2003). However, the background subtracted X-ray surface brightness maps show a bright ring in the outer 20% of the camera. We tried to get rid of this ring and contacted the XMM helpdesk and Read & Ponman, the authors of the background paper. However, up to this day, we did not entirely succeed to remove the brightness enhancement at the outer parts of the camera. Unfortunately, our results are somewhat sensitive to the uncertainty, as the radio galaxy 3C 129 is very large and occupies a rather large fraction of the XMM field of view. We are now working on a paper describing the results. The paper will include a detailed discussion of the uncertainties associated with the non- perfect background subtraction
Comparison of techniques to reconstruct VHE gamma-ray showers from multiple stereoscopic Cherenkov images
For air showers observed simultaneously by more than two imaging atmospheric
Cherenkov telescopes, the shower geometry is overconstrained by the images and
image information should be combined taking into account the quality of the
images. Different algorithms are discussed and tested experimentally using data
obtained from observations of Mkn 501 with the HEGRA IACT system. Most of these
algorithms provide an estimate of the accuracy of the reconstruction of shower
geometry on an event-by-event basis, allowing, e.g., to select higher-quality
subsamples for precision measurements.Comment: 14 Pages, 6 figures, Late
Thermal and Non-thermal Plasmas in the Galaxy Cluster 3C 129
We describe new Chandra spectroscopy data of the cluster which harbors the
prototypical "head tail" radio galaxy 3C 129 and the weaker radio galaxy 3C
129.1. We combined the Chandra data with Very Large Array (VLA) radio data
taken at 0.33, 5, and 8 GHz (archival data) and 1.4 GHz (new data). We also
obtained new HI observations at the Dominion Radio Astrophysical Observatory
(DRAO) to measure the neutral Hydrogen column density in the direction of the
cluster with arcminute angular resolution. The Chandra observation reveals
extended X-ray emission from the radio galaxy 3C 129.1 with a total luminosity
of 1.5E+41 erg/s. The X-ray excess is resolved into an extended central source
of ~2 arcsec (1 kpc) diameter and several point sources with an individual
luminosity up to 2.1E+40 erg/s. In the case of the radio galaxy 3C 129, the
Chandra observation shows, in addition to core and jet X-ray emission reported
in an earlier paper, some evidence for extended, diffuse X-ray emission from a
region east of the radio core. The 12 arcsec x 36 arcsec (6 kpc x 17 kpc)
region lies "in front" of the radio core, in the same direction into which the
radio galaxy is moving. We use the radio and X-ray data to study in detail the
pressure balance between the non-thermal radio plasma and the thermal Intra
Cluster Medium (ICM) along the tail of 3C 129 which extends over 15 arcmin (427
kpc). Depending on the assumed lower energy cutoff of the electron energy
spectrum, the minimum pressure of the radio plasma lies a factor of between 10
and 40 below the ICM pressure for a large part of the tail. We discuss several
possibilities to explain the apparent pressure mismatch.Comment: Accepted for publication in MNRAS. Refereed manuscript. 14 pages, 8
figures, additional panel of Fig. 3 shows asymmetric ICM distributio
Improved energy resolution for VHE gamma-ray astronomy with systems of Cherenkov telescopes
We present analysis techniques to improve the energy resolution of
stereoscopic systems of imaging atmospheric Cherenkov telescopes, using the
HEGRA telescope system as an example. The techniques include (i) the
determination of the height of the shower maximum, which is then taken into
account in the energy determination, and (ii) the determination of the location
of the shower core with the additional constraint that the direction of the
gamma rays is known a priori. This constraint can be applied for gamma-ray
point sources, and results in a significant improvement in the localization of
the shower core, which translates into better energy resolution. Combining both
techniques, the HEGRA telescopes reach an energy resolution between 9% and 12%,
over the entire energy range from 1 TeV to almost 100 TeV. Options for further
improvements of the energy resolution are discussed.Comment: 13 Pages, 7 figures, Latex. Astroparticle Physics, in pres
X-ray polarimetry with the Polarization Spectroscopic Telescope Array (PolSTAR)
This paper describes the Polarization Spectroscopic Telescope Array (PolSTAR), a mission proposed to NASA’s 2014 Small Explorer (SMEX) announcement of opportunity. PolSTAR measures the linear polarization of 3–50 keV (requirement; goal: 2.5–70 keV) X-rays probing the behavior of matter, radiation and the very fabric of spacetime under the extreme conditions close to the event horizons of black holes, as well as in and around magnetars and neutron stars. The PolSTAR design is based on the technology developed for the Nuclear Spectroscopic Telescope Array (NuSTAR) mission launched in June 2012. In particular, it uses the same X-ray optics, extendable telescope boom, optical bench, and CdZnTe detectors as NuSTAR. The mission has the sensitivity to measure ∼1% linear polarization fractions for X-ray sources with fluxes down to ∼5 mCrab. This paper describes the PolSTAR design as well as the science drivers and the potential science return
The Proposed High Energy Telescope (HET) for EXIST
The hard X-ray sky now being studied by INTEGRAL and Swift and soon by NuSTAR
is rich with energetic phenomena and highly variable non-thermal phenomena on a
broad range of timescales. The High Energy Telescope (HET) on the proposed
Energetic X-ray Imaging Survey Telescope (EXIST) mission will repeatedly survey
the full sky for rare and luminous hard X-ray phenomena at unprecedented
sensitivities. It will detect and localize (<20", at 5 sigma threshold) X-ray
sources quickly for immediate followup identification by two other onboard
telescopes - the Soft X-ray imager (SXI) and Optical/Infrared Telescope (IRT).
The large array (4.5 m^2) of imaging (0.6 mm pixel) CZT detectors in the HET, a
coded-aperture telescope, will provide unprecedented high sensitivity (~0.06
mCrab Full Sky in a 2 year continuous scanning survey) in the 5 - 600 keV band.
The large field of view (90 deg x 70 deg) and zenith scanning with
alternating-orbital nodding motion planned for the first 2 years of the mission
will enable nearly continuous monitoring of the full sky. A 3y followup pointed
mission phase provides deep UV-Optical-IR-Soft X-ray and Hard X-ray imaging and
spectroscopy for thousands of sources discovered in the Survey. We review the
HET design concept and report the recent progress of the CZT detector
development, which is underway through a series of balloon-borne wide-field
hard X-ray telescope experiments, ProtoEXIST. We carried out a successful
flight of the first generation of fine pixel large area CZT detectors
(ProtoEXIST1) on Oct 9, 2009. We also summarize our future plan (ProtoEXIST2 &
3) for the technology development needed for the HET.Comment: 10 pages, 13 figures, 2 tables, SPIE Conference "Astronomical
Telescopes and Instrumentation 2010"; to appear in Proceedings SPIE (2010
NEA Coordinating Group on Gas-Cooled Fast Reactor Development. Annual Progress Report of the Federal Republic of Germany 1975
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