Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “TeV gamma rays”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS2016

The First Fermi-LAT SNR Catalog and Cosmic Ray Implications

While supernova remnants (SNRs) are widely thought to be powerful cosmicray accelerators, indirect evidence comes from a small number of well-studied cases. Here we systematically determine the gamma-ray emission detected by the ermi Large Area Telescope (LAT) from all known Galactic SNRs, disentangling them from the sea of cosmic-ray generated photons in the Galactic plane. Using LAT data we have characterized the 1-100 GeV emission in 279 regions containing SNRs, accounting for systematic uncertainties caused by source misattribution and instrumental response. We classified 30 sources as SNRs, using spatial overlap with the radio emission position. For all the remaining regions we evaluated upper limits on SNRs' emission. In the First Fermi-LAT SNR Catalog there is a study of the common characteristics of these SNRs, such as comparisons between GeV, radio and TeV quantities. We show that previously satisfactory models of SNRs' GeV emission no longer adequately describe the data. To address the question of cosmic ray (CR) origins, we also examine the SNRs' maximal CR contribution assuming the GeV emission arises solely from proton interactions. Improved breadth and quality of multiwavelength (MW) data, including distances and local densities, and more, higher resolution gamma-ray data with correspondingly improved Galactic diffuse models will strengthen this constraint.

de Palma, F.↗
NASA NTRS1985

A cosmic ray super high energy multicore family event. 2: Structure and fragmentation characteristics of the jets

Quarks and gluons are not directly observable, but may be displayed through fragmentation in the form of hadronic jets, the evidence of which was first revealed in cosmic ray interactions before the advent of the modern theory of strong interactions. Experimental results from ISR and SPPS collider rendered the jet phenomena more confident and definite. All the properties of jets observed up to now at ISR and SPPS collider are in agreement with the predictions of QCD. In order to make further test of QCD in still higher energy regions, detailed study of super high energy jet events in cosmic rays is very desirable. The event KO E19 observed in the Mt. Kambala emulsion chamber is an interesting event for such study. The general features of KO E19 is described. Its total visible energy is sigma E sub gamma = 1537 TeV(E sub min = 1.5 TeV) and production height H=(70 + or - 30)m, with a hadron as its primary particle. Besides about forty small clusters, there are five super high energy cores or jets, one lying near the center of the event while the other four surrounding it, having incident directions making small angles with that of the primary particle. Detailed analysis is done on the emulsion plates inserted in the chamber, making full use of their fine granularity, superior in detecting and analyzing jet events, specially their substructures.

Source record↗
NASA NTRS2000

High-Energy Spectral Signatures in Gamma-Ray Bursts

One of the principal results obtained by the EGRET experiment aboard the Compton Gamma-Ray Observatory (CGRO) was the detection of several gamma-ray bursts (GRBs) above 100 MeV. The broad-band spectra obtained for these bursts gave no indication of any high energy spectral attenuation that might preclude detection of bursts by ground-based Cerenkov telescopes (ACTs), thus motivating several TeV observational programs. This paper explores the expectations for the spectral properties in the TeV and sub-TeV bands for bursts, in particular how attenuation of photons by pair creation internal to the source modifies the spectrum to produce distinctive spectral signatures. The energy of spectral breaks and the associated spectral indices provide valuable information that can constrain the bulk Lorentz factor of the GRB outflow at a given time. These characteristics define palpable observational goals for ACT programs, and strongly impact the observability of bursts in the TeV band.

Baring, Matthew G.↗
NASA NTRS2011

The 2010 Very High Energy Gamma-Ray Flare and 10 Years of Multi-Wavelength Observations of M87

The giant radio galaxy M87 with its proximity (16 Mpc), famous jet, and very massive black hole ((3-6) X 10(exp 9) Solar Mass) provides a unique opportunity to investigate the origin of very high energy (VHE; E>100 GeV) gamma-ray emission generated in relativistic outflows and the surroundings of super-massive black holes. M87 has been established as a VHE gamma -ray emitter since 2006. The VHE gamma -ray emission displays strong variability on timescales as short as a day. In this paper, results from a joint VHE monitoring campaign on M87 by the MAGIC and VERITAS instruments in 2010 are reported. During the campaign, a flare at VHE was detected. triggering further observations at VHE (H.E.S.S.), X-rays (Chandra), and radio (43 GHz VLBA). The excellent sampling of the VHE gamma-ray light curve enables one to derive a precise temporal characterization of the flare: the single, isolated flare is well described by a two-sided exponential function with significantly different flux rise and decay times of rise tau ((sup rise sub d) = (1:69 +/- 0:30) days and tau(sup decay sub d = (0:611 +/- 0:080) days, respectively. While the overall variability pattern of the 2010 flare appears somewhat different from that of previous VHE flares in 2005 and 2008, they share very similar timescales (approx day), peak fluxes (Phi (sub > 0:35 TeV) approx. equals (1 - 3) X 10(exp -11) ph / square cm/s), and VHE spectra. 43 GHz VLBA radio observations of the inner jet regions indicate no enhanced flux in 2010 in contrast to observations in 2008, where an increase of the radio flux of the innermost core regions coincided with a VHE flare. On the other hand, Chandra X-ray observations taken approx 3 days after the peak of the VHE gamma -ray emission reveal an enhanced flux from the core (flux increased by factor approx 2; variability timescale < 2 days). The long-term (2001-2010) multi-wavelength (MWL) light curve of M87, spanning from radio to VHE and including data from HST, LT, VLA and EVN, is used to further investigate the origin of the VHE gamma -ray emission. No unique, common MWL signature of the three VHE flares has been identified. In the outer kpc jet region, in particular in HST-1, no enhanced MWL activity was detected in 2008 and 2010, disfavoring it as the origin of the VHE flares during these years. Shortly after two of the three flares (2008 and 2010), the X-ray core was observed to be at a higher flux level than its characteristic range (determined from more than 60 monitoring observations: 2002-2009). In 2005, the strong flux dominance of HST-1 could have suppressed the detection of such a feature. Published models for VHE gamma -ray emission from M87 are reviewed in the light of the new data.

Abramowski, A.↗
NASA NTRS1999

High-Energy Spectral Signatures in Gamma-Ray Bursts

One of the principal results obtained by the EGRET experiment aboard the Compton Gamma-Ray Observatory (CGRO) was the detection of several gamma-ray bursts (GRBs) above 100 MeV. The broad-band spectra obtained for these bursts gave no indication of any high-energy spectral attenuation that might preclude detection of bursts by ground-based Cerenkov telescopes (ACTs), thus motivating several TeV observational programs. This paper explores the expectations for the spectral properties in the TeV and sub-TeV bands for bursts, in particular how attenuation of photons by pair creation internal to the source modifies the spectrum to produce distinctive spectral signatures. The energy of spectral breaks and the associated spectral indices provide valuable information that can constrain the bulk Lorentz factor of the GRB outflow at a given time. These characteristics define palpable observational goals for ACT programs, and strongly impact the observability of bursts in the TeV band.

Baring, Matthew D.↗
NASA NTRS1999

Recommended Priorities for NASA's Gamma Ray Astronomy Program 1999-2013

The Gamma-Ray Astronomy Program Working Group (GRAPWG) recommends priorities for the NASA Gamma-Ray Astronomy Program. The highest priority science topic is nuclear astrophysics and sites of gamma ray line emission. Other high priority topics are gamma ray bursts, hard x-ray emission from accreting black holes and neutron stars, the Advanced Compton Telescope (ACT), the High-resolution Spectroscopic Imager (HSI), and the Energetic X-ray Imaging Survey Telescope (EXIST). The recommendations include special consideration for technology development, TeV astronomy, the ultra-long duration balloon (ULDB) program, the International Space Station, optical telescope support, and data analysis and theory.

Carol, Ladd↗
NASA NTRS2020

CALET on the International Space Station: the first three years of observations

The CALorimetric Electron Telescope CALET is a space instrument designed to carry out precision measurements of high energy cosmic-rays on the JEM-EF external platform on the International Space Station, where it has been collecting science data continuously since mid-October 2015. In addition to its primary goal of identifying nearby sources of high-energy electrons and possible signatures of dark matter in the electron spectrum, CALET is carrying out extensive measurements of the energy spectra, relative abundances and secondary-to-primary ratios of elements from proton to iron, and even above (up to Z = 40), studying the details of galactic particle propagation and acceleration. An overview of CALET based on the data taken during the first three years of observations is presented, including a direct measurement of the electron+positron energy spectrum from 11 GeV to 4.8 TeV. The proton spectrum has been measured from 50 GeV to 10 TeV covering, for the first time with a single space-borne instrument, the whole energy interval previously investigated in separate sub-ranges by magnetic spectrometers and calorimetric instruments. Preliminary spectra of cosmic-ray nuclei are also presented, together with gamma-ray observations and searches for an e.m. counterpart of LIGO/ Virgo GW events.

P Brogi↗
NASA NTRS1985

Nuclear cascades in electromagnetic showers produced by primary gamma-quanta in the atmosphere

Distributions were calculated for the number of electrons N sub e, number of muons with the energy above 5 GeV N sub mu and the energy of hadron component E sub h in electromagnetic showers, produced by primary gamma-quanta with energies theta approx. equals 30 deg and observed at the mountain level 700 g/square centimeters. The mean number of nuclear interactions of photos with the energy above 5 GeV is about 0.3 per each TeV of the primary energy and nuclear cascades take out in average about 2% of the total shower energy. The mean number of 5 GeV muons for the electromagnetic shower is (2 to 5)% from the number of muons in cosmic ray showers with the same number of electrons at the observation level. similar value for the total energy of hadron component is also (2 to 5)%. N sub mu and N sub e values as well as E sub h and n sub e don't correlate at the fixed primary energy E sug gamma (o). Between N sub mu and E sub h there is a positive correlation at the given E sub gamma.

Danilova, T. V.↗
NASA NTRS1985

Electromagnetic and muonic structure of showers initiated by gamma-rays and by hadrons

If photon cascades develop by the usual mechanisms, there should indeed be notable differences between the structure of showers due to photon and hadron primaries, as regards muon densities and lateral distributions of some detector signals. The muon content of showers from Cygnus X-3, observed at Kiel, cannot be understood in this way. One remedy is to postulate arbitrarily a strong hadronic interaction of photons in the TeV region. This would utterly change the nature of electromagnetic cascades, but surprisingly does not at first sight seem to be in conflict with air shower observations.

Hillas, A. M.↗
DOE OSTI2024

Search for heavy dark matter from dwarf spheroidal galaxies: leveraging cascades and subhalo models

Abstract TheFermiLarge Area Telescope (Fermi-LAT) has been widely used to search for Weakly Interacting Massive Particle (WIMP) dark matter signals due to its unparalleled sensitivity in the GeV energy band. The leading constraints for WIMP byFermi-LAT are obtained from the analyses of dwarf spheroidal galaxies within the Local Group, which are compelling targets for dark matter searches due to their relatively low astrophysical backgrounds and high dark matter content. In the meantime, the search for heavy dark matter with masses above TeV remains a compelling and relatively unexplored frontier. In this study, we utilize 14-yearFermi-LAT data to search for dark matter annihilation and decay signals in 8 classical dwarf spheroidal galaxies within the Local Group. We consider secondary emission caused by electromagnetic cascades of prompt gamma rays and electrons/positrons from dark matter, which enables us to extend the search withFermi-LAT to heavier dark matter cases. We also update the dark matter subhalo model with informative priors respecting the fact that they reside in subhalos of our Milky Way halo aiming to enhance the robustness of our results. We place constraints on dark matter annihilation cross section and decay lifetime for dark matter masses ranging from 10 3 GeV to 10 11 GeV, where our limits are more stringent than those obtained by many other high-energy gamma-ray instruments.

Astronomy & Astrophysics↗
NASA NTRS1994

Neutrino bursts from gamma-ray bursts

If gamma-ray bursts originate at cosmological distances, as strongly indicated by the results from Burst and Transient Source Experiment (BATSE) on the Compton Gamma-Ray Observatory (CGRO), then ultrarelativistic ejecta are the likely consequence of the highly super-Eddington luminosity of the sources. If the energy injection rate varies with time, then the Lorentz factor of the wind also varies, and the shells of ejected matter collide with each other. The collisions between baryons produce pions which decay into high-energy photons, electrons, electron positron pairs, and neutrino pairs. The bulk Lorentz factor of approximately 300 is required if our model is to be compatible with the observed millisecond variability. The strongest gamma-ray bursts are observed to deliver approximately 10(exp -4) ergs/sq cm in 100-200 keV photons. In our scenario more energy may be delivered in a neutrino burst. Typical neutrinos may be approximately 30 GeV if the protons have a Maxwellian energy distribution, and up to approximately TeV if the protons have a power-law distribution. Such neutrino bursts are close to the detection limit of the DUMAND II experiment.

Paczynski, Bohdan↗
DOE OSTI2023

Limits on Neutrino Emission from GRB 221009A from MeV to PeV Using the IceCube Neutrino Observatory

Gamma-ray bursts (GRBs) have long been considered a possible source of high-energy neutrinos. While no correlations have yet been detected between high-energy neutrinos and GRBs, the recent observation of GRB 221009A—the brightest GRB observed by Fermi-GBM to date and the first one to be observed above an energy of 10 TeV—provides a unique opportunity to test for hadronic emission. In this paper, we leverage the wide energy range of the IceCube Neutrino Observatory to search for neutrinos from GRB 221009A. We find no significant deviation from background expectation across event samples ranging from MeV to PeV energies, placing stringent upper limits on the neutrino emission from this source.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1989

An upper limit on the high-energy gamma-ray emission of Vela X-1

The possibility of high-energy gamma-ray emission from the X-ray binary Vela X-1 was investigated by analyzing the COS-B satellite observations, using the COS-B X-ray detector for a phase coherent analysis in the search of rotational periodicity. The rotational upper limit is compared to the X-ray, TeV, and PeV fluxes reported by Chodil et al. (1967), North et al. (1984), and Protheroe et al. (1984), respectively. It was found that, under certain conditions, the upper limit determined here is not inconsistent with the reports of TeV and PeV emission.

Mattox, J. R.↗
NASA NTRS2010

New Results on High Energy Cosmic Ray Electrons Observed with Fermi LAT and Their Implications on the Origin of Cosmic Rays

The Large Area Telescope on-board the Fermi Gamma-Ray Space Telescope has collected more than 10 million cosmic ray electrons with energy above 7 GeV since its science operation on orbit. High energy electrons rapidly lose their energy by synchrotron radiation on Galactic magnetic fields and by inverse Compton scattering on the interstellar radiation field. The typical distance over which a 1 TeV electron loses half its total energy is estimated to be 300-400 pc.This makes them a unique tool for probing nearby Galactic space. Observed spectrum has a harder spectral index than was previously reported and suggests the presence of nearby sources of high energy electrons. One of viable candidates are nearby pulsars, possibly some of recently discovered by Fermi. At the same time the dark matter origin of such sources cannot be ruled out. I will also report our current upper limits on cosmic ray electrons anisotropy which helps to set constraints on their local sources.

Moiseev, Alexander↗
NASA NTRS2016

Deep View of the Large Magellanic Cloud with Six Years of Fermi-LAT Observations

Context. The nearby Large Magellanic Cloud (LMC) provides a rare opportunity of a spatially resolved view of an external star-forming galaxy in gamma-rays. The LMC was detected at 0.1-100 GeV as an extended source with CGRO/EGRET and using early observations with the Fermi-LAT. The emission was found to correlate with massive star-forming regions and to be particularly bright towards 30 Doradus. Aims. Studies of the origin and transport of cosmic rays (CRs) in the Milky Way are frequently hampered by line-of-sight confusion and poor distance determination. The LMC offers a complementary way to address these questions by revealing whether and how the gamma-ray emission is connected to specific objects, populations of objects, and structures in the galaxy. Methods. We revisited the gamma-ray emission from the LMC using about 73 months of Fermi-LAT P7REP data in the 0.2-100 GeV range. We developed a complete spatial and spectral model of the LMC emission, for which we tested several approaches: a simple geometrical description, template-fitting, and a physically driven model for CR-induced interstellar emission. Results. In addition to identifying PSR J0540-6919 through its pulsations, we find two hard sources positionally coincident with plerion N 157B and supernova remnant N 132D, which were also detected at TeV energies with H.E.S.S. We detect an additional soft source that is currently unidentified. Extended emission dominates the total flux from the LMC. It consists of an extended component of about the size of the galaxy and additional emission from three to four regions with degree-scale sizes. If it is interpreted as CRs interacting with interstellar gas, the large-scale emission implies a large-scale population of approximately 1-100 GeV CRs with a density of approximately 30% of the local Galactic value. On top of that, the three to four small-scale emission regions would correspond to enhancements of the CR density by factors 2 to 6 or higher, possibly more energetic and younger populations of CRs compared to the large-scale population. An alternative explanation is that this is emission from an unresolved population of at least two dozen objects, such as pulsars and their nebulae or supernova remnants. This small-scale extended emission has a spatial distribution that does not clearly correlate with known components of the LMC, except for a possible relation to cavities and supergiant shells. Conclusions. The Fermi-LAT GeV observations allowed us to detect individual sources in the LMC. Three of the newly discovered sources are associated with rare and extreme objects. The 30 Doradus region is prominent in GeV gamma-rays because PSR J0540-6919 and N 157B are strong emitters. The extended emission from the galaxy has an unexpected spatial distribution, and observations at higher energies and in radio may help to clarify its origin.

gamma rays: galaxies – Magellanic Clouds – cos↗
NASA NTRS1985

Observations of potential ultra high energy gamma-ray sources above 10(15) eV

The Haverah Park 50 m water-Cerenkov array has been used to examine a number of periodic sources for ultra high energy gamma-ray emission above 10 to the 15th power eV. The data, recorded between 1 Jan. 1979 and 31 Dec. 1984, feature a modest angular resolution of approx 3 deg with millisecond arrival time resolution post 1982. The sources investigated include the Crab pulsar, Her X-1, Au0115 + 63 and Geminga. All objects have been detected by workers in the TeV region, with varying degrees of confidence.

Lambert, A.↗
NASA NTRS1979

Diffuse fluxes of cosmic high-energy neutrinos

Production spectra of high-energy neutrinos from galactic cosmic-ray interactions with interstellar gas and extragalactic ultrahigh-energy cosmic-ray interactions with microwave blackbody photons are presented and discussed. These production processes involve the decay of charged pions and are thus related to the production of cosmic gamma rays from the decay of neutral pions. Estimates of the neutrino fluxes from various diffuse cosmic sources are then made, and the reasons for significant differences with previous estimates are discussed. Small predicted event rates for a DUMAND (deep underwater muon and neutrino detector) type detection system, combined with a possible significant flux of prompt neutrinos from the atmosphere above 50 TeV, may make the study of diffuse extraterrestrial neutrinos more difficult than previously thought.

Stecker, F. W.↗
NASA NTRS1994

Very high energy gamma rays from active galactic nuclei: Cascading on the cosmic background radiation fields and the formation of pair halos

Recent high-energy gamma-ray observations (E(sub gamma) greater than 100 MeV) of blazar Active Galactic Nuclei (AGNs) show emission spectra with no clear upper energy cutoff. AGNs, considered to be possible sources for the observed flux of cosmic rays beyond 10(exp 19) eV, may well have emission extending into the very high energy (VHE), (E(sub gamma) greater than 100 GeV) domain. Because VHE gamma-rays are absorbed by pair production on the intergalactic background radiation fields, much of this emission may not be directly visible. The electromagnetic cascades initiated by absorbed VHE gamma-rays, however, may be observable. Since, most probably, the velocities of (e(+), e(-)) pairs produced in a cascade are quickly isotropized by an ambient random magnetic field, extended 'halos' (R greater than 1 Mpc) of pairs will be formed around AGNs with VHE emission. The cascade radiation from these pair halos is emitted isotropically and should be observable at energies below a few TeV. The halo radiation can be distinguished by its characteristic variation in spectrum and intensity with angular distance from the central source. This variation depends weakly on the details of the central source model, e.g., the orientation and beaming/opening angle of an emitting jet. Limiting or determining the intensity of the pair halo can thus serve as a model-independent bound on or measure of the VHE power of AGNs. Next-generation Cherenkov telescopes may be able to image a pair halo.

Aharonian, F. A.↗