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Search Results: 1 - 10 of 138782 matches for " K. Kosack "
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TeV Observations of the Galactic Center
K. Kosack
Physics , 2003,
Abstract: We present the results of 16 hours of ongoing observations of the galactic center region (including Sagittarius A*) with the Whipple High Energy Gamma-Ray Telescope. We apply a data analysis method optimized for large zenith angle observations on an independent Crab Nebula data set. We discuss possible systematic problems associated with observations of extended sources in the galactic plane.
XMM-Newton and Chandra X-ray follow-up observations of the VHE gamma-ray source HESS J1507-622
O. Tibolla,S. Kaufmann,K. Kosack
Physics , 2014, DOI: 10.1051/0004-6361/201321778
Abstract: Context. The discovery of the unique source HESS J1507-622 in the very high energy (VHE) range (100 GeV-100 TeV) opened new possibilities to study the parent population of ultra-relativistic particles found in astrophysical sources and underlined the possibility of new scenarios/mechanisms crucial for understanding the underlying astrophysical processes in nonthermal sources. Aims. The follow-up X-ray (0.2 - 10 keV) observations on HESS J1507-622 are reported, and possibilities regarding the nature of the VHE source and that of the newly discovered X-ray sources are investigated. Methods.We obtained bservations with the X-ray satellites XMM-Newton and Chandra. Background corrections were applied to the data to search for extended diffuse emission. Since HESS J1507-622 covers a large part of the field of view of these instruments, blank-sky background fields were used. Results. The discovery of several new X-ray sources and a new, faint, extended X-ray source with a flux of ~6e-14 erg cm^-2 s^-1 is reported. Interestingly, a new, variable point-like X-ray source with a flux of ~8e-14 erg cm^-2 s^-1 appeared in the 2011 observation, which was not detected in the previous X-ray observations. Conclusions. The X-ray observations revealed a faint, extended X-ray source that may be a possible counterpart for HESS J1507-622. This source could be an X-ray pulsar wind nebula (PWN) remnant of the larger gamma-ray PWN, which is still bright in IC emission. Several interpretations are proposed to explain the newly detected variable X-ray source.
A new method of reconstructing very-high-energy gamma-ray spectra: the Template Background Spectrum
M. V. Fernandes,D. Horns,K. Kosack,M. Raue,G. Rowell
Physics , 2014, DOI: 10.1051/0004-6361/201323156
Abstract: Very-high-energy (VHE, E>0.1 TeV) gamma-ray emission regions with angular extents comparable to the field-of-view of current imaging air-Cherenkov telescopes (IACT) require additional observations of source-free regions to estimate the background contribution to the energy spectrum. This reduces the effective observation time and deteriorates the sensitivity. A new method of reconstructing spectra from IACT data without the need of additional observations of source-free regions is developed. Its application is not restricted to any specific IACT or data format. On the basis of the template background method, which defines the background in air-shower parameter space, a new spectral reconstruction method from IACT data is developed and studied, the Template Background Spectrum (TBS); TBS is tested on published H.E.S.S. data and H.E.S.S. results. Good agreement is found between VHE gamma-ray spectra reported by the H.E.S.S. collaboration and those re-analysed with TBS. This includes analyses of point-like sources, sources in crowded regions, and of very extended sources down to sources with fluxes of a few percent of the Crab Nebula flux and excess-to-background ratios around 0.1. However, the TBS background normalisation introduces new statistical and systematic errors which are accounted for, but may constitute a limiting case for very faint extended sources. The TBS method enables the spectral reconstruction of data when other methods are hampered or even fail. It does not need dedicated observations of VHE gamma-ray-free regions (e.g. as the On/Off background does) and circumvents known geometrical limitations to which other methods (e.g. the reflected-region background) for reconstructing spectral information of VHE gamma-ray emission regions are prone to; TBS would be, in specific cases, the only feasible way to reconstruct energy spectra.
Influence of aerosols from biomass burning on the spectral analysis of Cherenkov telescopes
R. de los Reyes,J. Hahn,K. Bernloehr,P. Krueger,C. Deil,H. Gast,K. Kosack,V. Marandon
Physics , 2013,
Abstract: During the last decade, imaging atmospheric Cherenkov telescopes (IACTs) have proven themselves as astronomical detectors in the very-high-energy (VHE; E>0.1 TeV) regime. The IACT technique observes the VHE photons indirectly, using the Earth's atmosphere as a calorimeter. Much of the calibration of Cherenkov telescope experiments is done using Monte Carlo simulations of the air shower development, Cherenkov radiation and detector, assuming certain models for the atmospheric conditions. Any deviation of the real conditions during observations from the assumed atmospheric model will result in a wrong reconstruction of the primary gamma-ray energy and the resulting source spectra. During eight years of observations, the High Energy Stereoscopic System (H.E.S.S.) has experienced periodic natural as well as anthropogenic variations of the atmospheric transparency due to aerosols created by biomass burning. In order to identify data that have been taken under such long-term reductions in atmospheric transparency, a new monitoring quantity, the Cherenkov transparency coefficient, has been developed and will be presented here. This quantity is independent of hardware changes in the detector and, therefore, isolates atmospheric factors that can impact the performance of the instrument, and in particular the spectral results. Its positive correlation with independent measurements of the atmospheric optical depth (AOD) retrieved from data of the Multi-angle Imaging SpectroRadiometer (MISR) on board of the Terra NASA's satellite is also presented here.
OmniMapFree: A unified tool to visualise and explore sequenced genomes
John Antoniw, Andrew M Beacham, Thomas K Baldwin, Martin Urban, Jason J Rudd, Kim E Hammond-Kosack
BMC Bioinformatics , 2011, DOI: 10.1186/1471-2105-12-447
Abstract: We have developed a generic software which permits users to view a single genome in entirety either within its chromosome or supercontig context within a single window. This software permits the genome to be displayed at any scales and with any features. Different data types and data sets are displayed onto the genome, which have been acquired from other types of studies including classical genetics, forward and reverse genetics, transcriptomics, proteomics and improved annotation from alternative sources. In each display, different types of information can be overlapped, then retrieved in the desired combinations and scales and used in follow up analyses. The displays generated are of publication quality.OmniMapFree provides a unified, versatile and easy-to-use software tool for studying a single genome in association with all the other datasets and data types available for the organism.In the late 1990s, the first fully sequenced genome of a eukaryotic organism emerged as a result of a huge community effort. The annotated genome of Saccharomyces cerevisiae was subsequently published [1] and a comprehensive genome browser has gradually evolved [2,3]. The success of this whole genome sequencing (WGS) project using the Sanger method, paved the way for other model species as well as industrially, agriculturally and medically important species to be nominated for WGS [4]. Within a few years and following the development of several next generation sequencing technologies, the number of eukaryotic species for which complete or near completely sequenced genomes became available steadily rose [5]. Also for the species initially sequenced other strains with different biological properties and closely related species have now been sequenced or nominated for sequencing to provide important clusters of genomic information. In agricultural, environmental and medical research, many species of interest have small to medium sized genomes. For example, free living and pathogenic fu
New unidentified H.E.S.S. Galactic sources
O. Tibolla,R. C. G. Chaves,O. de Jager,W. Domainko,A. Fiasson,N. Komin,K. Kosack
Physics , 2009,
Abstract: H.E.S.S. is one of the most sensitive instruments in the very high energy (VHE; > 100 GeV) gamma-ray domain and has revealed many new sources along the Galactic Plane. After the successful first VHE Galactic Plane Survey of 2004, H.E.S.S. has continued and extended that survey in 2005-2008, discovering a number of new sources, many of which are unidentified. Some of the unidentified H.E.S.S. sources have several positional counterparts and hence several different possible scenarios for the origin of the VHE gamma-ray emission; their identification remains unclear. Others have so far no counterparts at any other wavelength. Particularly, the lack of an X-ray counterpart puts serious constraints on emission models. Several newly discovered and still unidentified VHE sources are reported here.
HESS J1507-622: an unique unidentified source off the Galactic Plane
O. Tibolla,W. Domainko,W. Hofmann,O. de Jager,S. Kaufmann,N. Komin,K. Kosack,for the H. E. S. S. Collaboration
Physics , 2009,
Abstract: Galactic very high energy (VHE, > 100 GeV) gamma ray sources in the inner Galaxy H.E.S.S. survey tend to cluster within 1 degree in latitude around the Galactic plane. HESS J1507-622 instead is unique, since it is located at latitude of ~3.5 degrees. HESS J1507-622 is slightly extended over the PSF of the instrument and hence its Galactic origin is clear. The search for counterparts in other wavelength regimes (radio, infrared and X-rays) failed to show any plausible counterparts; and given its position off the Galactic plane and hence the absorption almost one order of magnitude lower, it is very surprising to not see any counterparts especially at X-rays wavelengths (by ROSAT, XMM Newton and Chandra). Its latitude implies that it is either rather close, within about 1 kpc, or is located well off the Galactic plane. And also the models reflect the uniqueness of this object: a leptonic PWN scenario would place this source due to its quite small extension to multi-kpc distance whereas a hadronic scenario would preferentially locate this object at distances of < 1 kpc where the density of target material is higher.
Broadband multi-wavelength campaign on PKS 2005-489
S. Kaufmann,M. Hauser,K. Kosack,M. Raue,O. Tibolla,F. Volpe,S. Wagner,for the HESS collaboration,P. Fortin,W. McConville,D. J. Thompson,for the Fermi/LAT collaboration
Physics , 2009,
Abstract: The spectral energy distribution (SED) of high-frequency peaked BL Lac objects (HBL) is characterized by two peaks: one in the UV-X-ray and one in the GeV-TeV regime. An interesting object for analyzing these broadband characteristics is PKS 2005-489, which in 2004 showed the softest TeV spectrum ever measured. In 2009, a multi-wavelength campaign has been conducted with, for the first time, simultaneous observations by H.E.S.S. (TeV), Fermi/LAT (GeV), RXTE (keV), Swift (keV, UV, optical) and ATOM (optical) to cover the two peaks of the SED. During this campaign PKS 2005-489 underwent a high state in all wavebands which gives the opportunity to study in detail the emission processes of a high state of this interesting HBL.
New unidentified Galactic H.E.S.S. sources
O. Tibolla,R. C. G. Chaves,W. Domainko,O. de Jager,S. Kaufmann,S. Wagner,N. Komin,K. Kosack,A. Fiasson,M. Renaud,for the H. E. S. S. Collaboration
Physics , 2009,
Abstract: H.E.S.S. is one of the most sensitive instruments in the very high energy (VHE; > 100 GeV) gamma-ray domain and has revealed many new sources along the Galactic Plane. After the successful first VHE Galactic Plane Survey of 2004, H.E.S.S. has continued and extended that survey in 2005-2008, discovering a number of new sources, many of which are unidentified. Some of the unidentified H.E.S.S. sources have several positional counterparts and hence several different possible scenarios for the origin of the VHE gamma-ray emission; their identification remains unclear. Others have so far no counterparts at any other wavelength. Particularly, the lack of an X-ray counterpart puts serious constraints on emission models. Several newly discovered and still unidentified VHE sources are reported here.
Unidentified Gamma-Ray Sources as Ancient Pulsar Wind Nebulae
O. C. de Jager,S. E. S. Ferreira,A. Djannati-Ata?,M. Dalton,C. Deil,K. Kosack,M. Renaud,U. Schwanke,O. Tibolla
Physics , 2009,
Abstract: In this paper we explore the evolution of a PWN while the pulsar is spinning down. An MHD approach is used to simulate the evolution of a composite remnant. Particular attention is given to the adiabatic loss rate and evolution of the nebular field strength with time. By normalising a two component particle injection spectrum (which can reproduce the radio and X-ray components) at the pulsar wind termination shock to the time dependent spindown power, and keeping track with losses since pulsar/PWN/SNR birth, we show that the average field strength decreases with time as $t^{-1.3}$, so that the synchrotron flux decreases, whereas the IC gamma-ray flux increases, until most of the spindown power has been dumped into the PWN. Eventually adiabatic and IC losses will also terminate the TeV visibility and then eventually the GeV visibility.
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