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Search Results: 1 - 10 of 4377 matches for " Omar Tibolla "
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Gamma-rays from pulsar wind nebulae in starburst galaxies
Karl Mannheim,Dominik Els?sser,Omar Tibolla
Physics , 2010, DOI: 10.1016/j.astropartphys.2012.02.009
Abstract: Recently, gamma-ray emission at TeV energies has been detected from the starburst galaxies NGC253 (Acero et al., 2009) and M82 (Acciari et al., 2009. It has been claimed that pion production due to cosmic rays accelerated in supernova remnants interacting with the interstellar gas is responsible for the observed gamma rays. Here, we show that the gamma-ray pulsar wind nebulae left behind by the supernovae contribute to the TeV luminosity in a major way. A single pulsar wind nebula produces about ten times the total luminosity of the Sun at energies above 1 TeV during a lifetime of 10^5 years. A large number of 3x10^4 pulsar wind nebulae expected in a typical starburst galaxy at a distance of 4 Mpc can readily produce the observed TeV gamma rays.
A search for VHE counterparts of Galactic Fermi bright sources and MeV to TeV spectral characterization
P. H. Thomas Tam,Stefan Wagner,Omar Tibolla,Ryan Chaves
Physics , 2009, DOI: 10.1051/0004-6361/200913717
Abstract: Very high-energy (VHE; E>100 GeV) gamma-rays have been detected from a wide range of astronomical objects, such as pulsar wind nebulae (PWNe), supernova remnants (SNRs), giant molecular clouds, gamma-ray binaries, the Galactic Center, active galactic nuclei (AGN), radio galaxies, starburst galaxies, and possibly star-forming regions as well. At lower energies, observations using the Large Area Telescope (LAT) onboard Fermi provide a rich set of data which can be used to study the behavior of cosmic accelerators in the MeV to TeV energy bands. In particular, the improved angular resolution of current telescopes in both bands compared to previous instruments significantly reduces source confusion and facilitates the identification of associated counterparts at lower energies. In this paper, a comprehensive search for VHE gamma-ray sources which are spatially coincident with Galactic Fermi/LAT bright sources is performed, and the available MeV to TeV spectra of coincident sources are compared. It is found that bright LAT GeV sources are correlated with TeV sources, in contrast to previous studies using EGRET data. Moreover, a single spectral component seems unable to describe the MeV to TeV spectra of many coincident GeV/TeV sources. It has been suggested that gamma-ray pulsars may be accompanied by VHE gamma-ray emitting nebulae, a hypothesis that can be tested with VHE observations of these pulsars.
A search for VHE counterparts of galactic Fermi sources
P. H. Thomas Tam,Stefan Wagner,Omar Tibolla,Ryan Chaves
Physics , 2010,
Abstract: Very high-energy (VHE; E > 100 GeV) gamma-rays have been detected from a wide range of astronomical objects, such as SNRs, pulsars and pulsar wind nebulae, AGN, gamma-ray binaries, molecular clouds, and possibly star-forming regions as well. At lower energies, sources detected using Large Area Telescope (LAT) aboard Fermi provide a rich set of data which can be used to study the behavior of cosmic accelerators in the GeV to TeV energy bands. In particular, the improved angular resolution in both bands compared to previous instruments significantly reduces source confusion and facilitates the identification of associated counterparts at lower energies. In this talk, a comprehensive search for VHE gamma-ray sources which are spatially coincident with Galactic Fermi/LAT bright sources is performed, and the GeV to TeV spectra of selected coincident sources are shown. It is found that LAT bright GeV sources are correlated to TeV sources, in contrast with previous studies using EGRET data.
Are most of the VHE gamma-ray unidentified sources relic PWNe?
Omar Tibolla,Michael Vorster,Sarah Kaufmann,Stefan Ferreira,Karl Mannheim
Physics , 2013,
Abstract: The evolution of Pulsar Wind Nebulae (PWNe) plays a crucial role in interpreting the very high energy (VHE; > 10^11 eV) gamma-ray unidentified sources; and moreover it represents the only viable option to explain the discovery of several "dark sources" in the TeV gamma-ray (i.e. VHE gamma-ray sources without lower energies, radio or X-ray counterparts). The newest time-dependent modeling of PWNe presented in [1] and [2] has to be tested on a broader sample of young well-known PWNe and applied to the full-sample of "dark sources". The consequences of this interpretation go far beyond the interpretation of "dark sources": e.g. there could be strong implication in the origin of cosmic rays and (when considering a leptonic origin of the gamma-ray signal) they can be important for reinterpreting the detection of starburst galaxies in the TeV gamma-ray band.
No X-Ray Excess from the HESS J1741-302 Region except a New Intermediate Polar Candidate
Hideki Uchiyama,Katsuji Koyama,Hironori Matsumoto,Omar Tibolla,Sarah Kaufmann,Stefan Wagner
Physics , 2011, DOI: 10.1093/pasj/63.sp3.S865
Abstract: With the Suzaku satellite, we observed an unidentified TeV gamma-ray source HESS J1741$-$302 and its surroundings. No diffuse or point-like X-ray sources are detected from the bright southern emission peak of HESS J1741$-$302. From its neighborhood, we found a new intermediate polar candidate at the position of $(\alpha, \delta)_{\rm J2000.0} = (\timeform{17h40m35.6s}, \timeform{-30D14m16s})$, which is designated as Suzaku J174035.6$-$301416. The spectrum of Suzaku J174035.6$-$301416 exhibits emission lines at the energy of 6.4, 6.7 and 7.0 keV, which can be assigned as the K$\alpha$ lines from neutral, He-like and H-like iron, respectively. A coherent pulsation is found at a period of 432.1 $\pm$ 0.1 s. The pulse profile is quasi-sinusoidal in the hard X-ray band (4$-$8 keV), but is more complicated in the soft X-ray band (1$-$3 keV). The moderate period of pulsation, the energy flux, and the presence of the iron K$\alpha$ lines indicate that Suzaku J174035.6$-$301416 is likely an intermediate polar, a subclass of magnetized white dwarf binaries (cataclysmic variables). Based on these discoveries, we give some implications on the origin of GCDX and brief comments on HESS J1741$-$302 and PSR B1737$-$30.
The 2013 multiwavelength campaign on the Narrow-Line Seyfert 1 galaxy 1H 0323+342: a rosetta stone for the jet/disk paradigm
Omar Tibolla,Sarah Kaufmann,Luigi Foschini,Karl Mannheim,Shu Zhang,Jian Li,Emmanouil Angelakis,Lars Fuhrmann,Paul Haeusner,Jannik Kania,Dominik Elsaesser,Annika Kreikenbohm,Robert Schulz,Matthias Kadler
Physics , 2013,
Abstract: Narrow-Line Seyfert 1 galaxies have been established as a new class of gamma-ray emitting AGN with relatively low black hole masses, but near-Eddington accretion rates. Other extragalactic gamma-ray sources observed so far such as Flat Spectrum Radio Quasars, Radio Galaxies, and BL Lacertae Objects generally exhibit much higher black hole masses and, in the case of BL Lac objects and FRI Radio Galaxies, much lower accretions rates. The multifrequency campaign of 2013 centered on the bright source 1H 0323+342 will provide further insights into the nature of the jets and their gamma ray production mechanisms in a largely unexplored corner of AGN parameter space. Here, we show preliminary results of this campaign and discuss them.
Recent Results from the MAGIC Telescopes
O. Tibolla,for the MAGIC collaboration
Physics , 2012,
Abstract: MAGIC (Major Atmospheric Gamma-ray Imaging Cherenkov Telescope) is a system of two 17 meters Cherenkov telescopes, sensitive to very high energy (VHE; $> 10^{11}$ eV) gamma radiation above an energy threshold of 50 GeV. The first telescope was built in 2004 and operated for five years in stand-alone mode. A second MAGIC telescope (MAGIC-II), at a distance of 85 meters from the first one, started taking data in July 2009. Together they integrate the MAGIC stereoscopic system. Stereoscopic observations have improved the MAGIC sensitivity and its performance in terms of spectral and angular resolution, especially at low energies. We report on the status of the telescope system and highlight selected recent results from observations of galactic and extragalactic gamma-ray sources. The variety of sources discussed includes pulsars, galactic binary systems, clusters of galaxies, radio galaxies, quasars, BL Lacertae objects and more.
Extended X-ray jet and TeV emission in a low frequency peaked BL Lac object
S. Kaufmann,S. J. Wagner,O. Tibolla
Physics , 2011, DOI: 10.7529/ICRC2011/V08/1287
Abstract: BL Lac objects are known to have very energetic jets pointing towards the observer under small viewing angles. Many of these show high luminosity over the whole energy range up to TeV, mostly classified as high-energy peaked BL Lac objects. Recently, TeV gamma-ray emission was detected from a low-energy peaked BL Lac object. Interestingly, this source has also a clear detection of an X-ray jet. We present a detailed study of this X-ray jet and its connection to the radio jet as well as a study of the underlying physical processes in the energetic jet, producing emission from the radio to the TeV range.
Discovery of an extended X-ray jet in AP Librae
S. Kaufmann,S. J. Wagner,O. Tibolla
Physics , 2013, DOI: 10.1088/0004-637X/776/2/68
Abstract: Chandra observations of the low-energy peaked BL Lac object AP Librae revealed the clear discovery of a non-thermal X-ray jet. AP Lib is the first low energy peaked BL Lac object with an extended non-thermal X-ray jet that shows emission into the VHE range. The X-ray jet has an extension of ~15'' (~ 14 kpc). The X-ray jet morphology is similar to the radio jet observed with VLA at 1.36 GHz emerging in south-east direction and bends by 50 degrees at a distance of 12'' towards north-east. The intensity profiles of the X-ray emission are studied consistent with those found in the radio range. The spectral analysis reveals that the X-ray spectra of the core and jet region are both inverse Compton dominated. This adds to a still small sample of BL Lac objects whose X-ray jets are IC dominated and thus more similar to the high luminosity FRII sources than to the low luminosity FRI objects, which are usually considered to be the parent population of the BL Lac objects.
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.
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