Download or read book Detection of Soft Gamma Ray Emission from the Seyfert II Galaxy NGC 4507 by the OSSE Telescope Preprint written by and published by . This book was released on 1995 with total page 11 pages. Available in PDF, EPUB and Kindle. Book excerpt: We report the first soft gamma-ray observation by the OSSE experiment onboard the CGRO of the optically selected Seyfert II galaxy, NGC 4507. The source was observed on two separate weeks in 1993 and detected between 50 and 200 keV at a confidence level of 7 . There is no evidence of flux variability within or between the two observation periods which sample timescales from days to months. The source spectrum obtained from combining the two sets of data is best described by spectral forms including some exponential cutoff. The observed shape is steeper than the one observed by GINGA in the X-ray band in 1990. The joint GINGA/OSSE spectrum is best described by an absorbed power law exponentially cutoff at high energies and having an iron K alpha emission line. Comparison between NGC 4507 and other Seyfert galaxies indicate that although at low energies a difference between type I and II objects is possible (but still weak in this specific case) at high energies the observed shapes are indeed similar. We interpret this as evidence that the primary source emission (i.e. not reprocessed by material in the source) is the same for both types; this finding is in agreement with the unified scheme of Seyfert galaxies. Apart from its own interest, the OSSE detection of hard X-ray emission from a Seyfert II galaxy is also important for the implications it has on the contribution of Seyfert galaxies of both types to the cosmic diffuse background, as type II objects are expected to outnumber type I sources.

Download or read book The Energetic Gamma Ray Experiment Telescope EGRET Science Symposium written by Carl Fichtel and published by . This book was released on 1990 with total page 354 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Gamma ray Large Area Space Telescope written by and published by . This book was released on 1998 with total page 32 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Analysis of the Recent TSF Secondary Gamma ray Experiment written by F. L. Keller and published by . This book was released on 1958 with total page 56 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book High Resolution Imaging of Brackett Gamma and H 2 1 0 S 1 Emission in the Seyfert Galaxy NGC 1 068 written by and published by . This book was released on 1990 with total page 17 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Models of X ray and Gamma ray Emissions from Seyfert Galaxies written by Roland Svensson and published by . This book was released on 1996 with total page 6 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Calibration of the EGRET Gamma Ray Telescope with a Back scattered Laser Beam written by John Richard Mattox and published by . This book was released on 1987 with total page 316 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Gamma ray and Cosmic ray Detectors Techniques and Missions written by Brian D. Ramsey and published by SPIE-International Society for Optical Engineering. This book was released on 1996 with total page 656 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Concept and Design Studies for the Exploration of High Energy Gamma Ray Astronomy on the Gamma Ray Observatory written by Lorna Campbell Finman and published by . This book was released on 1983 with total page 560 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Gamma ray Studies of the Young Shell type SNR RX J1713 7 3946 written by and published by . This book was released on 2014 with total page 86 pages. Available in PDF, EPUB and Kindle. Book excerpt: One of the most significant current discussions in Astrophysics relates to the origin of high-energy cosmic rays. According to our current knowledge, the abundance distribution of the elements in cosmic rays at their point of origin indicates, within plausible error limits, that they were initially formed by nuclear processes in the interiors of stars. It is also believed that their energy distribution up to 1018 eV has Galactic origins. But even though the knowledge about potential sources of cosmic rays is quite poor above " 1015 eV, that is the "knee" of the cosmic-ray spectrum, up to the knee there seems to be a wide consensus that supernova remnants are the most likely candidates. Evidence of this comes from observations of non-thermal X-ray radiation, requiring synchrotron electrons with energies up to 1014 eV, exactly in the remnant of supernovae. To date, however, there is not conclusive evidence that they produce nuclei, the dominant component of cosmic rays, in addition to electrons. In light of this dearth of evidence, [gamma]-ray observations from supernova remnants can offer the most promising direct way to confirm whether or not these astrophysical objects are indeed the main source of cosmic-ray nuclei below the knee. Recent observations with space- and ground-based observatories have established shell-type supernova remnants as GeV-to- TeV [gamma]-ray sources. The interpretation of these observations is however complicated by the different radiation processes, leptonic and hadronic, that can produce similar fluxes in this energy band rendering ambiguous the nature of the emission itself. The aim of this work is to develop a deeper understanding of these radiation processes from a particular shell-type supernova remnant, namely RX J1713.7-3946, using observations of the LAT instrument onboard the Fermi Gamma-Ray Space Telescope. Furthermore, to obtain accurate spectra and morphology maps of the emission associated with this supernova remnant, an improved model of the diffuse Galactic [gamma]-ray emission background is developed. The analyses of RX J1713.7-3946 carried out with this improved background show that the hard Fermi-LAT spectrum cannot be ascribed to the hadronic emission, leading thus to the conclusion that the leptonic scenario is instead the most natural picture for the high-energy [gamma]-ray emission of RX J1713.7-3946. The leptonic scenario however does not rule out the possibility that cosmic-ray nuclei are accelerated in this supernova remnant, but it suggests that the ambient density may not be high enough to produce a significant hadronic [gamma]-ray emission. Further investigations involving other supernova remnants using the improved back- ground developed in this work could allow compelling population studies, and hence prove or disprove the origin of Galactic cosmic-ray nuclei in these astrophysical objects. A break- through regarding the identification of the radiation mechanisms could be lastly achieved with a new generation of instruments such as CTA.

Download or read book A New Population of Very High energy Gamma ray Sources Detected with H E S S in the Inner Part of the Milky Way written by and published by . This book was released on with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The H.E.S.S., experiment (High Energy Stereoscopic System) is an array of four imaging Cherenkov telescopes designed to detect gamma-rays in the energy domain above 100 GeV. The telescopes utilise the stereoscopic approach, in which particle showers in the atmosphere are observed by several telescopes simultaneously, connected by a central trigger system at the hardware level. This approach greatly reduces the background of the instrument and thereby allows one to decrease the energy threshold and improve the sensitivity of the system. The functionality and performance of the central trigger of H.E.S.S., is presented. Making use of the reduced energy threshold and the improved sensitivity, a survey of the inner part of the Milky way in very high energy gamma-rays, was conducted in 2004 with H.E.S.S. at an unprecedented sensitivity level. The Galactic plane between +- 30deg, in longitude and +-3deg, in latitude relative to the Galactic centre was observed for a total of 230 hours, reaching an average flux sensitivity of 3% of the Crab nebula at energies above 200 GeV. Fourteen new sources were detected at a significance level greater than 4 sigma in addition to three previously known sources in this area. Detailed spectral and morphological information for these new sources are provided, along with a discussion on possible counterparts in other wavelength bands. The distribution in galactic latitude of the detected sources appears to be consistent with a scale height in the galactic disc for the parent population of less than 100 parsec.

Download or read book The Soft Gamma Ray Spectrum of A0535 26 Detection of an Absorption Feature at 110 KeV by OSSE written by and published by . This book was released on 1995 with total page 16 pages. Available in PDF, EPUB and Kindle. Book excerpt: We present soft gamma-ray observations by the Oriented Scintillation Spectrometer Experiment (OSSE) on the Compton Gamma Ray Observatory (GRO) of the transient X-ray binary pulsar A0535+26. The observations were made 1994 February 8[17, immediately prior to the peak of a giant outburst. The phase- averaged spectrum is complex and cannot be described by a single-component model. We find that structure in the spectrum above 100 keV can best be modeled by an absorption feature near 110 keV, which we interpret as the signature of cyclotron resonant scattering. Because of OSSE's 45-keV threshold, we are unable to make a definitive statement on the presence of a 55-keV absorption line; however we can conclude that if this line does exist, it must have a smaller optical depth than the line at 110 keV. A first harmonic (= fundamental) cyclotron resonance at 110 keV corresponds to a magnetic field strength at the surface of the neutron star of ~1 x 10(exp 13) G (~5 x 10(exp 12) G if the first harmonic is at 55 keV).

Download or read book The Energetic Gamma Ray Experiment Telescope EGRET Science Symposium written by Carl E. Fichtel and published by . This book was released on 1990 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Diffuse ray Emission Observed by the Fermi Large Telescope written by Luigi Tibaldo and published by . This book was released on 2011 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Galactic diffuse gamma-ray emission is produced by interactions of cosmic rays with interstellar gas and low-energy radiation fields is the brightest component of the high-energy gamma-ray sky, surveyed since 2008 with unprecedented sensitivity and angular resolution by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope. Galactic diffuse emission constitutes not on bright and structured background which needs to be modeled in order to study individual sources and fainter diffuse components, but it can be used also as a probe of the interstellar environment of the Milky Way. We present in-depth studies of LAT g-ray observations of selected regions in the local and outer Galaxy. LAT data are compared v multiwavelength tracers of the interstellar medium, including radio/mm-wave lines of gas and infrared emission/extinction from dust On one hand, we discuss the constraints provided by the gamma-ray data on the census of the interstellar gas. We determine the ratio X(CO)=N(H2)/W(CO) for several clouds and we also find evidence for an ubiquitous dark phase of interstellar gas which does not shine; at other wavelengths. On the other hand, we use the emissivity per hydrogen atom to infer the distribution of cosmic rays in distant locations not accessible by direct measurements. A remarkably hard and extended excess of gamma-rays is detected in the innermost 100 pc of the massive-star forming region in Cygnus.

Download or read book Development of an Advanced Gamma hadron Separation Technique and Application to Particular Gamma ray Sources with H E S S written by and published by . This book was released on with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The High Energy Stereoscopic system, H.E.S.S. is an array of four imaging atmospheric Cherenkov telescopes, designed for the study of non-thermal phenomena in the universe at very high energies (VHE). The sensitivity of telescope systems such as H.E.S.S. can considerably be improved by a better discrimination of the vast number of hadronic cosmic-ray background events against the very rare gamma-ray signal events. In this work, an elaborated discrimination technique - the Boosted Decision Tree method - has been developed and its capabilities in terms of gamma/hadron separation and improved sensitivity are demonstrated. In the second part, the BDT method is applied to data obtained in observations of massive star forming environments, namely the colliding wind binary [eta] Carinae, the massive stellar cluster Westerlund 1 and the Starburst galaxy NGC 253. An upper limit on the gamma-ray flux of the famous colliding wind binary system [eta] Carinae is derived and, for the first time, an alternative model for the high-energy emission observed by the Fermi satellite is presented. The detection of very extended VHE gamma-ray emission from the vicinity of Westerlund 1 is reported and thorough spectral and morphological tests are presented. Large parts of the resolved emission can be explained in a hadronic scenario, however, a decisive conclusion can not be drawn. Finally, the BDT method allowed to detect the first Starburst galaxy, namely NGC253, in VHE gamma rays. Spectral and morphological results are presented and suggest that large parts of the CR energy content are convectively and diffusively transported into the intergalactic medium.

Download or read book VLBI Study of Water Maser Emission in the Seyfert 2 Galaxy NGC 5793 I Imaging Blueshifted Emission and the Parsec scale Jet written by Yoshiaki Hagiwara and published by . This book was released on 2001 with total page 16 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Rosat Detection of Diffuse Hot Gas in the Edge On Galaxy Ngc 4631 written by National Aeronautics and Space Administration (NASA) and published by Createspace Independent Publishing Platform. This book was released on 2018-07-11 with total page 26 pages. Available in PDF, EPUB and Kindle. Book excerpt: ROSAT observation is presented of the edge-on spiral galaxy NGC 4631, a nearby Sc/SBd galaxy best known for its extended radio halo. Because of the low foreground Galactic X-ray-absorbing gas column density, N(sub H) approximately 1.4 x 10(exp 20)cm(exp -2), this observation is sensitive to gas of temperature greater than or equal to a few times 10(exp 5) K. A soft (approximately 0.25 keV) X-ray radiation out to more than 8 kpc above the midplane of the galaxy was detected. The strongest X-ray emission in the halo is above the central disk, a region of about 3 kpc radius which shows high star formation activity. The X-ray emission in the halo is bordered by two extended filaments of radio continuum emission. Diffuse X-ray emission from hot gas in the galaxy's disk was found. The spectrum of the radiation can be characterized by a thermal plasma with a temperature of 3 x 10(exp 6) K and a radiative cooling rate of approximately 8 x 10(exp 39) ergs s(exp -1). This rate is only a few percent of the estimated supernova energy release in the interstellar medium of the galaxy. Analysis of the X-ray spectrum shows evidence for the presence of a cooler (several times 10(exp 5) K) halo gas component that could consume a much larger fraction of the supernova energy. Strong evidence was found for disk/halo interaction. Hot gas apparently blows out from supershells in the galaxy's disk at a rate of approximately 1 solar mass yr(exp -1). This outflow of hot gas drags magnetic field lines up in the halo and forms a magnetized gaseous halo. If the magnetic field lines are still anchored to the disk gas at large disk radii, the outflowing gas may be confined high above the disk by magnetic pressure. A strong X-ray source which coincides spatially with an H I supershell has been identified. However, the source is likely an extremely luminous X-ray binary with L(sub chi)(0.1 - 2 keV) approximately 5 x 10(exp 39) ergs s(exp -1), which makes it a stellar mass black hole candidate. Wang...