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NASA NTRS1985

Peculiarities of gamma-quanta distribution at 20 TeV energy

The angular distribution of protons from the fragmentational region is analyzed. The gamma-quanta families are generated in a dense target by cosmic ray particles at 20 Tev energy. Families were found which had dense groups (spikes) of gamma-quanta where the rapidity/density is 3 times more than the average value determined for all registered families. The experimental data is compared with the results of artificial families simulation.

Ermakov, P. M.↗
NASA NTRS2005

Neutrino Emission in the Hadronic Synchrotron Mirror Model: The "Orphan" Flare from 1ES 1959+650

A challenge to standard leptonic synchrotron self-Compton (SSC) models is the so-called orphan TeV flares, i.e., enhanced very high energy (VHE) gamma-ray emission without any contemporaneous X-ray flaring activity, that have recently been observed in TeV blazars (e.g., 1ES 1959+650). In order to explain the orphan TeV flare of 1 ES 1959+650 observed in 2002 June, the so-called hadronic synchrotron mirror model has been developed. Here relativistic protons are proposed to exist in the jet and interact with reflected electron synchrotron radiation of the precursor SSC flare. If the reflector is located in the cloud region, time shifts of several days are possible between the precursor and the orphan flare. The external photons, blue-shifted in the comoving jet frame, are able to excite the Delta(1232) resonance when interacting with protons of Lorentz factors gamma(sub p) approx. 10(exp 3)-10(exp 4). The decay products of this resonance include charged pions, which, on decay, give rise to neutrino production during the orphan flare. In this paper we calculate the expected neutrino emission for the 2002 June 4 orphan TeV flare of 1ES 1959+650. We compare our results with the recent observations of AMANDA-II of a neutrino event in spatial and temporal coincidence with the orphan flare of this blazar. We find that the expected neutrino signal from the hadronic synchrotron mirror model is insufficient to explain the claimed neutrino signal from the direction of 1ES 1959+650.

Reimer, A.↗
NASA NTRS1998

Study of MeV/GeV/Sources. TeV Extension of First CGRO EGRET Catalogue Sources Multiwavelength Blazar Studies: A Search for TeV Emission from Bursts Detected by BATSE

The Whipple Gamma Ray Collaboration was formed in 1982 with the aim of improving the sensitivity of the ground-based atmospheric Cherenkov technique by the use of imaging cameras on large optical detectors. The approach was successful and the discipline of ground-based TeV astronomy was established. The first confirmed galactic source was discovered by the Whipple Collaboration as were the first two extragalactic sources. The technique has now matured and several new and important astrophysical results have been produced. The gamma-ray group of the Smithsonian Astrophysical Observatory is a key component of the Whipple Gamma Ray Collaboration. With all its members resident in Arizona, all its activities are devoted to research in ground-based gamma-ray astronomy.

Weekes, Trevor C.↗
NASA NTRS2006

Intergalactic Photon Spectra from the Far-IR to the UV Lyman Limit for 0 < z < 6 and the Optical Depth of the Universe to High-Energy Gamma Rays

We calculate the intergalactic photon density as a function of both energy and redshift for 0<z<6 for photon energies from.003 eV to the Lyman limit cutoff at 13.6 eV in a (Omega)CDM universe with (Omega)(Lambda)=0.7 and (Omega)m=0.3. The basic features of our backward-evolution model for galaxies were developed in earlier papers by Malkan & Stecker. With a few improvements, we find that this evolutionary model gives predictions of new deep number counts from Spitzer, as well as a calculation of the spectral energy distribution of the diffuse infrared background, which are in good agreement with the data. We then use our calculated intergalactic photon densities to extend previous work on the absorption of high-energy Gamma-rays in intergalactic space owing to interactions with low-energy photons and the 2.7 K cosmic microwave background radiation. We calculate the optical depth of the universe, Tau , for Gamma-rays having energies from 4 GeV to 100 TeV emitted by sources at redshifts from 0 to 5. We also give an analytic fit with numerical coefficients for approximating (E(Gamma), z). As an example of the application of our results, we calculate the absorbed spectrum of the blazar PKS 2155-304 at z=0.117 and compare it with the spectrum observed by the HESS air Cerenkov Gamma-ray telescope array.

Stecker, F. W.↗
NASA NTRS2012

Reconstructing the Gamma-Ray Photon Optical Depth of the Universe To Z Approx. 4 from Multiwavelength Galaxy Survey Data

Reconstructing the Gamma-Ray Photon Optical Depth of the Universe To Z Approx. 4fFrom Multiwavelength Galaxy Survey Data We reconstruct the gamma-ray opacity of the universe out to z approx. < 3–4 using an extensive library of 342 observed galaxy luminosity function (LF) surveys extending to high redshifts .We cover the whole range from UV to mid-IR (0.15–25 micron ) providing for the first time a robust empirical calculation of the gamma gamma optical depth out to several TeV. Here, we use the same database as Helgason et al. where the extragalactic background light was reconstructed from LFs out to 4.5 micron and was shown to recover observed galaxy counts to high accuracy. We extend our earlier library Of LFs to 25micron such that it covers the energy range of pair production with gamma -rays (1) in the entire Fermi/LAT energy range, and (2) at higher TeV energies probed by ground-based Cherenkov telescopes. In the absence of significant contributions to the cosmic diffuse background from unknown populations, such as the putative Population III era sources, the universe appears to be largely transparent to gamma-rays at all Fermi/LAT energies out to z approx.. 2 whereas it becomes opaque to TeV photons already at z approx. < 0.2 and reaching tau approx∼ 10 at z = 1. Comparing with the currently available Fermi/LAT gamma-ray burst and blazar data shows that there is room for significant emissions originating in the first stars era.

galaxies:evolution↗
NASA NTRS1996

[A NASA / University Joint Venture in Space Science]

MILAGRO is a water-Cherenkov detector for observing cosmic gamma rays over a broad energy range of 100 GeV to 100 TeV. MILAGRO will be the first detector that has sensitivity overlapping both air-Cherenkov and air-shower detectors. With this detector scientists in the collaboration will study previously observed celestial sources at their known emission energies, extend these observations into a new energy regime, and search for new sources at unexplored energies. The diffuse gamma-radiation component in our galaxy, which originates from interactions of cosmic rays with interstellar gas and photons, provides important information about the density, distribution, and spectrum of the cosmic rays that pervade the interstellar medium. Events in the Compton Gamma Ray Observatory (GRO) are being observed up to about 30 GeV, differing by slightly more than order of magnitude from the low energy threshold of MILAGRO. By looking in coincidence at sources, correlated observations will greatly extend the astrophysics potential of MILAGRO and NASA's GRO. A survey of cosmic-ray observatories is being prepared for scientists and others to provide a resource and reference which describes high energy cosmic-ray research activities around the world. This summary presents information about each research group, such as names of principal investigators, number of persons in the collaboration, energy range, sensitivity, angular resolution, and surface area of detector. Similarly, a survey of gamma-ray telescopes is being prepared to provide a resource and reference which describes gamma-ray telescopes for investigating galactic diffuse gamma-ray flux currently observed in the GeV energy range, but is expected to extend into the TeV range. Two undergraduate students are compiling information about gamma-ray telescopes and high energy cosmic-ray observatories for these surveys. Funding for this project was provided by the Arkansas Space Grant Consortium. Also enclosed Appendix A, B, C, D and E.

Wold, Donald C.↗
NASA NTRS1985

High energy neutrino astronomy with MACRO

A large area underground detector with accurate muon tracking and directionality can be used for the search of extraterrestrial sources of high energy neutrinos. The sensitivity of the MACRO detector to possible sources of neutrinos was evaluated with a Monte-Carlo simulation of the neutrino interaction in the rock and and of the detection in the real apparatus. Two categories of possible neutrino sources are discussed in comparison with the detector sensitivity. Promising candidate objects for this search appear to be the two binary X-ray sources in the southern key Vela X1 and LMC X4, which are known to emit gamma rays up to the 10,000 TeV region.

Auriemma, G.↗
NASA NTRS2019

MAGIC and Fermi-LAT gamma-ray results on unassociated HAWC sources

The HAWC Collaboration released the 2HWC catalogue of TeV sources, in which 19 show no association with any known high-energy (HE; E ≳ 10 GeV) or very-high-energy (VHE; E ≳ 300 GeV) sources. This catalogue motivated follow-up studies by both the Major Atmospheric Gamma-ray Imaging Cherenkov (MAGIC) and Fermi-LAT (Large Area Telescope) observatories with the aim of investigating gamma-ray emission over a broad energy band. In this paper, we report the results from the first joint work between High Altitude Water Cherenkov (HAWC), MAGIC, and Fermi-LAT on three unassociated HAWC sources: 2HWC J2006+341, 2HWC J1907+084*, and 2HWC J1852+013*. Although no significant detection was found in the HE and VHE regimes, this investigation shows that a minimum 1° extension (at 95 per cent confidence level) and harder spectrum in the GeV than the one extrapolated from HAWC results are required in the case of 2HWC J1852+013*, whilst a simply minimum extension of 0.16° (at 95 per cent confidence level) can already explain the scenario proposed by HAWC for the remaining sources. Moreover, the hypothesis that these sources are pulsar wind nebulae is also investigated in detail.

M. L. Ahnen↗
NASA NTRS2014

Detailed Investigation of the Gamma-Ray Emission in the Vicinity of SNR W28 with FERMI-LAT

We present a detailed investigation of the Gamma-ray emission in the vicinity of the supernova remnant (SNR) W28 (G6.4−0.1) observed by the Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope. We detected significant γ -ray emission spatially coincident with TeV sources HESS J1800−240A, B, and C, located outside the radio boundary of the SNR. Their spectra in the 2-100 GeV band are consistent with the extrapolation of the power-law spectra of the TeV sources. We also identified a new source of GeV emission, dubbed Source W, which lies outside the boundary of TeV sources and coincides with radio emission from the western part of W28. All of the GeV Gamma-ray sources overlap with molecular clouds in the velocity range from 0 to 20 km s (exp−1). Under the assumption that the Gamma-ray emission toward HESS J1800−240A, B, and C comes from 3.14(exp0) decay due to the interaction between the molecular clouds and cosmic rays (CRs) escaping from W28, they can be naturally explained by a single model in which the CR diffusion coefficient is smaller than the theoretical expectation in the interstellar space. The total energy of the CRs escaping from W28 is constrained through the same modeling to be larger than is approximately 2 × 10(exp49) erg. The emission from Source W can also be explained with the same CR escape scenario.

cosmic rays↗
NASA NTRS1985

Detection threshold energy of high energy cascade showers using thermoluminescence PTFE-sheet and hot-gas reader

A new thermoluminescence (TL) sheet was developed as a detector for high energy components in air showers. For the investigation of detection threshold energy for a cascade showeer, TL sheets were exposed at Mt. Fuji with X ray films in emulsion chambers and were scanned by a hot-gas reader. It is concluded that if a gamma ray whose energy is more than 6 TeV enters vertically into lead chambers, the resulting cascade shower is readily detectable at maximum development.

Kino, S.↗
NASA NTRS2014

NuSTAR Discovery Of A Young, Energetic Pulsar Associated with the Luminous Gamma-Ray Source HESS J1640-465

We report the discovery of a 206 ms pulsar associated with the TeV gamme-ray source HESS J1640−465 using the Nuclear Spectroscopic Telescope Array (NuSTAR) X-ray observatory. PSR J1640−4631 lies within the shelltype supernova remnant (SNR) G338.3−0.0, and coincides with an X-ray point source and putative pulsar wind nebula (PWN) previously identified in XMM-Newton and Chandra images. It is spinning down rapidly with period derivative P = 9.758(44) × 10(exp −13), yielding a spin-down luminosity E = 4.4 × 10(exp 36) erg s(exp −1), characteristic age tau(sub c) if and only if P/2 P = 3350 yr, and surface dipole magnetic field strength B(sub s) = 1.4×10(exp 13) G. For the measured distance of 12 kpc to G338.3−0.0, the 0.2-10 TeV luminosity of HESS J1640−465 is 6% of the pulsar's present E. The Fermi source 1FHL J1640.5−4634 is marginally coincident with PSR J1640−4631, but we find no gamma-ray pulsations in a search using five years of Fermi Large Area Telescope (LAT) data. The pulsar energetics support an evolutionary PWN model for the broadband spectrum of HESS J1640−465, provided that the pulsar's braking index is n approximately equal to 2, and that its initial spin period was P(sub 0) approximately 15 ms.

pulsars: individual↗
NASA NTRS2007

GLAST Large Area Telescope Multiwavelength Planning

Gamma-ray astrophysics depends in many ways on multiwavelength studies. The Gamma-ray Large Area Space Telescope (GLAST) Large Area Telescope (LAT) Collaboration has started multiwavelength planning well before the scheduled 2007 launch of the observatory. Some of the high-priority multiwavelength needs include: (1) availability of contemporaneous radio and X-ray timing of pulsars; (2) expansion of blazar catalogs, including redshift measurements; (3) improved observations of molecular clouds, especially at high galactic latitudes; (4) simultaneous broad-spectrum blazar monitoring; (5) characterization of gamma-ray transients, including gamma ray bursts; (6) radio, optical, X-ray and TeV counterpart searches for reliable and effective sources identification and characterization. Several of these activities are needed to be in place before launch.

Reimer, O.↗
NASA NTRS2019

CALET Results After Three Years on Orbit on the International Space Station

The CALorimetric Electron Telescope (CALET) is an astroparticle physics experiment installed on the International Space Station since August 2015. The CALET mission was conceived to address several outstanding questions of high-energy astroparticle physics, like indirect detection of dark matter, the origin of cosmic rays (CRs), their mechanisms of acceleration and galactic propagation, the presence of possible nearby astrophysical CR sources. That can be achieved by precise measurements of the fluxes of CR electrons and gamma-rays up to the unexplored region above 1 TeV, and the energy spectra and composition of CR nuclei from a few tens of GeV to hundreds of TeV. In order to perform these observations, the instrument combines a thick total absorption PWO crystal calorimeter for energy measurement, a scintillator hodoscope for charge identi cation and thin imaging tungsten-scintillating fiber calorimeter providing accurate particle tracking and complementary charge measurement. In this paper, we will present an overview of the main CALET results based on the data collected in the first three years of the mission.

P Maestro↗
NASA NTRS1992

Constraints on electron acceleration in the Crab nebula

Using the radio through hard X-ray images of the Crab nebula to derive the spatial dependence of the electron spectrum and the magnetic field distribution from MHD flow models, we have rederived the high-energy spectrum of inverse Compton scattered gamma rays. We find agreement with the observed spectrum at TeV energies, but it is clear that the inverse Compton flux does not contribute significantly to the unpulsed nebular emission observed by COS-B from 50 to 500 MeV, which is consistent with a smooth continuation of the spectrum in hard X-rays. The emission at these energies must therefore be due to synchrotron radiation by electrons of at least PeV energies. It appears that the emission in the high-energy gamma-ray range, sensitive to the highest energy electrons in the nebula, can put interesting constraints on the acceleration mechanism.

Harding, A. K.↗
NASA NTRS1985

Intensities of high-energy cosmic rays at Mount Kanbala

General features of family events with Summary E sub gamma 200 TeV, observed by the emulsion chambers at Mt. Kanbala, are presented in comparison with the Monte Carlo simulation. The lateral and cluster structure, and the energy spectra of constituent gamma-rays and hadrons are shown to be consistent with the Monte Carlo results calculated under the assumption of heavy-enriched primary, scaling, QCD jets and increasing cross-section.

Ren, J. R.↗
NASA NTRS2020

Fermi Large Area Telescope Fourth Source Catalog

We present the fourth Fermi Large Area Telescope catalog (4FGL) of gamma-ray sources. Based on the first eight years of science data from the Fermi Gamma-ray Space Telescope mission in the energy range from 50 MeV to 1 TeV, it is the deepest yet in this energy range. Relative to the 3FGL catalog, the 4FGL catalog has twice as much exposure as well as a number of analysis improvements, including an updated model for the Galactic diffuse gamma-ray emission, and two sets of light curves (one-year and two-month intervals). The 4FGL catalog includes 5064 sources above 4 sigma significance, for which we provide localization and spectral properties. Seventy-five sources are modeled explicitly as spatially extended, and overall, 358 sources are considered as identified based on angular extent, periodicity, or correlated variability observed at other wavelengths. For 1336 sources, we have not found plausible counterparts at other wavelengths. More than 3130 of the identified or associated sources are active galaxies of the blazar class, and 239 are pulsars.

S. Abdollahi↗
NASA NTRS1992

Detection of TeV photons from the active galaxy Markarian 421

The detection of TeV energy photons from the giant elliptical galaxy Markarian 421 using the Whipple Observatory gamma-ray telescope is reported. The signal has a statistical significance of 6 sigma above background and the flux above 0.5 TeV is 0.3 of that from the Crab Nebula. The source location agrees with the position of Mk 421 within the angular uncertainty of the Whipple instrument.

Punch, M.↗
NASA NTRS2000

Gamma-ray Pulsars: Models and Predictions

Pulsed emission from gamma-ray pulsars originates inside the magnetosphere, from radiation by charged particles accelerated near the magnetic poles or in the outer gaps. In polar cap models, the high energy spectrum is cut off by magnetic pair production above an energy that is, dependent on the local magnetic field strength. While most young pulsars with surface fields in the range B = 10(exp 12) - 10(exp 13) G are expected to have high energy cutoffs around several GeV, the gamma-ray spectra of old pulsars having lower surface fields may extend to 50 GeV. Although the gamma-ray emission of older pulsars is weaker, detecting pulsed emission at high energies from nearby sources would be an important confirmation of polar cap models. Outer gap models predict more gradual high-energy turnovers of the primary curvature emission around 10 GeV, but also predict an inverse Compton component extending to TeV energies. Detection of pulsed TeV emission, which would not survive attenuation at the polar caps, is thus an important test of outer gap models. Next-generation gamma-ray telescopes sensitive to GeV-TeV emission will provide critical tests of pulsar acceleration and emission mechanisms.

Harding Alice K.↗