GeV Energy Range Research Articles

Spallation Neutron Sources and Accelerator-Driven Systems

Spallation neutron sources are the primary accelerator-driven source of intense neutrons. They require high power proton accelerators in the GeV energy range coupled to heavy metal targets for efficient neutron production. They form the basis of large scale neutron scattering facilities, and are essential elements in accelerator-driven subcritical reactors. Demanding technology has been developed which is enabling the next generation of spallation neutron sources to reach even higher neutron fluxes. This technology sets the stage for future deployment in accelerator-driven systems and neutron sources for nuclear material irradiation.

INTERACTING COSMIC RAYS WITH MOLECULAR CLOUDS: A BREMSSTRAHLUNG ORIGIN OF DIFFUSE HIGH-ENERGY EMISSION FROM THE INNER 2°×1° OF THE GALACTIC CENTER

The high energy activity in the inner few degrees of the Galactic center is traced by diffuse radio, X-ray and gamma-ray emission. The physical relationship between different components of diffuse gas emitting at multiple wavelengths is a focus of this work. We first present radio continuum observations using Green Bank Telescope and model the nonthermal spectrum in terms of a broken power-law distribution of GeV electrons emitting synchrotron radiation. We show that the emission detected by Fermi is primarily due to nonthermal bremsstrahlung produced by the population of synchrotron emitting electrons in the GeV energy range interacting with neutral gas. The extrapolation of the electron population measured from radio data to low and high energies can also explain the origin of FeI 6.4 keV line and diffuse TeV emission, as observed with Suzaku, XMM-Newton, Chandra and the H.E.S.S. observatories. The inferred physical quantities from modeling multi-wavelength emission in the context of bremsstrahlung emission from the inner 300x120 parsecs of the Galactic center are constrained to have the cosmic ray ionization rate 1-10x10^{-15} s^-1, molecular gas heating rate elevating the gas temperature to 75-200K, fractional ionization of molecular gas 10^{-6} to 10^{-5}, large scale magnetic field 10-20 micro Gauss, the density of diffuse and dense molecular gas 100 and 10^3 cm^{-3} over 300pc and 50pc pathlengths, and the variability of FeI Kalpha 6.4 keV line emission on yearly time scales. Important implications of our study are that GeV electrons emitting in radio can explain the GeV gamma-rays detected by Fermi and that the cosmic ray irradiation model, like the model of the X-ray irradiation triggered by past activity of Sgr A*, can also explain the origin of the variable 6.4 keV emission from Galactic center molecular clouds.

Observations of the magnetars 4U 0142+61 and 1E 2259+586 with the MAGIC telescopes

Magnetars are an extreme, highly magnetized class of isolated neutron stars whose large X-ray luminosity is believed to be driven by their high magnetic field. In this work we study for the first time the possible very high energy gamma-ray emission above 100 GeV from magnetars, observing the sources 4U 0142+61 and 1E 2259+586. We observed the two sources with atmospheric Cherenkov telescopes in the very high energy range (E > 100 GeV). 4U 0142+61 was observed with the MAGIC I telescope in 2008 for ~25 h and 1E 2259+586 was observed with the MAGIC stereoscopic system in 2010 for ~14 h. The data were analyzed with the standard MAGIC analysis software. Neither magnetar was detected. Upper limits to the differential and integral flux above 200 GeV were computed using the Rolke algorithm. We obtain integral upper limits to the flux of 1.52*10^-12cm^-2 s^-1 and 2.7*10^-12cm^-2 s^-1 with a confidence level of 95% for 4U 0142+61 and 1E 2259+586, respectively. The resulting differential upper limits are presented together with X-ray data and upper limits in the GeV energy range.

Simulating GeV particles in a very large scintillating detector

Large liquid scintillation detectors could be an alternative to water Cherenkov and liquid argon detectors for high energy neutrino measurements, in the GeV energy range, suitable for both cosmic ray studies and a long baseline neutrino experiment. We demonstrate the ability of a 65 ktonne detector to distinguish the lepton flavor, and show a track finder.

MAGIC observations of the giant radio galaxy M 87 in a low-emission state between 2005 and 2007

We present the results of a long M87 monitoring campaign in very high energy $\gamma$-rays with the MAGIC-I Cherenkov telescope. We aim to model the persistent non-thermal jet emission by monitoring and characterizing the very high energy $\gamma$-ray emission of M87 during a low state. A total of 150\,h of data were taken between 2005 and 2007 with the single MAGIC-I telescope, out of which 128.6\,h survived the data quality selection. We also collected data in the X-ray and \textit{Fermi}--LAT bands from the literature (partially contemporaneous). No flaring activity was found during the campaign. The source was found to be in a persistent low-emission state, which was at a confidence level of $7\sigma$. We present the spectrum between 100\,GeV and 2\,TeV, which is consistent with a simple power law with a photon index $\Gamma=2.21\pm0.21$ and a flux normalization at 300\,GeV of $(7.7\pm1.3) \times 10^{-8}$ TeV$^{-1}$ s$^{-1}$ m$^{-2}$. The extrapolation of the MAGIC spectrum into the GeV energy range matches the previously published \textit{Fermi}--LAT spectrum well, covering a combined energy range of four orders of magnitude with the same spectral index. We model the broad band energy spectrum with a spine layer model, which can satisfactorily describe our data.

Searches for sterile neutrinos with IceCube DeepCore

We show that study of the atmospheric neutrinos in the 10--100 GeV energy range by DeepCore sub-array of the IceCube Neutrino Observatory can substantially constrain the mixing of sterile neutrinos of mass $\sim 1$ eV with active neutrinos. In the scheme with one sterile neutrino we calculate $\nu_\mu-$ and $\bar{\nu}_\mu-$ oscillation probabilities as well as zenith angle distributions of $\nu_\mu^{CC}$ events in different energy intervals in DeepCore. The distributions depend on the mass hierarchy of active neutrinos. Therefore, in principle, the hierarchy can be identified, if $\nu_s$ exists. After a few years of exposure the DeepCore data will allow to exclude the mixing $|U_{\mu 4}|^2 \geq 0.02$ indicated by the LSND/MiniBooNE results. Combination of the DeepCore and high energy IceCube data will further improve sensitivity to $\nu_s$ mixing parameters.

A model for the two component γ-ray spectra observed from the γ-ray binaries

ABSTRACT Observations of two well-known binary systems (LS 5039 and LS I +61 303) with the satellite and Cherenkov telescopes revealed the broad-band γ-ray spectra which seems to show two components, the first at GeV energies, showing exponential cut-off at a few GeV, and the second at TeV energies which does not fit well to the extrapolation of spectrum from the GeV energy range. We propose that such two component spectrum is produced by two populations of electrons which appear within the binary system as a result of acceleration on a double shock structure separated by a contact discontinuity. Such structure is created within the binary system as a result of the interaction of the pulsar and massive star winds. The shocks from the side of the pulsar and the massive star have different proprieties which allow acceleration of electrons to different maximum energies. These two populations of electrons produce two component γ-ray spectra caused by the Inverse Compton (IC) scattering of stellar radiation. The example calculations, performed in terms of the anisotropic IC e± pair cascade model, for the location of the pulsar at the periastron and apastron passages confirm the high-energy emission features observed from LS I +61 303.

An electromagnetic calorimeter for the JLab real compton scattering experiment

A lead–glass hodoscope calorimeter that was constructed for use in the Jefferson Lab Real Compton Scattering experiment is described. The detector provides a measurement of the coordinates and the energy of scattered photons in the GeV energy range with resolutions of 5 mm and 6%/ E γ GeV . Features of both the detector design and its performance in the high luminosity environment during the experiment are presented.

HESS J1943+213: a candidate extreme BL Lacertae object

We report on a newly detected point-like source, HESS J1943+213 located in the Galactic plane. This source coincides with an unidentified hard X-ray source IGR J19443+2117, which was proposed to have radio and infrared counterparts. HESS J1943+213 is detected at the significance level of 7.9 \sigma (post-trials) at RA(J2000)=19h 43m 55s +- 1s (stat) +- 1s (sys), DEC(J2000) = +21deg 18' 8" +- 17" (stat) +- 20" (sys). The source has a soft spectrum with photon index Gamma = 3.1 +- 0.3 (stat) +- 0.2 (sys) and a flux above 470 GeV of 1.3 +- 0.2 (stat) +- 0.3 (sys) x 10^{-12} cm^{-2} s^{-1}. There is no Fermi/LAT counterpart down to a flux limit of 6 x 10^{-9} cm^{-2} s^{-1} in the 0.1-100 GeV energy range (95% confidence upper limit calculated for an assumed power-law model with a photon index Gamma=2.0). The data from radio to VHE gamma-rays do not show any significant variability. We combine new H.E.S.S., Fermi/LAT and Nancay Radio Telescope observations with pre-existing non-simultaneous multi-wavelength observations of IGR J19443+2117 and discuss the likely source associations as well as the interpretation as an active galactic nucleus, a gamma-ray binary or a pulsar wind nebula. The lack of a massive stellar counterpart disfavors the binary hypothesis, while the soft VHE spectrum would be very unusual in case of a pulsar wind nebula. In addition, the distance estimates for Galactic counterparts places them outside of the Milky Way. All available observations favor an interpretation as an extreme, high-frequency peaked BL Lac object with a redshift z>0.14. This would be the first time a blazar is detected serendipitously from ground-based VHE observations, and the first VHE AGN detected in the Galactic Plane.

Measurement of neutrino-induced charged-current charged pion production cross sections on mineral oil atEν∼1 GeV

Using a high-statistics, high-purity sample of νμ-induced charged current, charged pion events in mineral oil (CH2), MiniBooNE reports a collection of interaction cross sections for this process. This includes measurements of the CCπ+ cross section as a function of neutrino energy, as well as flux-averaged single- and double-differential cross sections of the energy and direction of both the final-state muon and pion. In addition, each of the single-differential cross sections are extracted as a function of neutrino energy to decouple the shape of the MiniBooNE energy spectrum from the results. In many cases, these cross sections are the first time such quantities have been measured on a nuclear target and in the 1 GeV energy range.21 MoreReceived 17 November 2010DOI:https://doi.org/10.1103/PhysRevD.83.052007© 2011 American Physical Society

Indirect detection of dark matter, current status and recent results

Since its launch in 2008, the Large Area Telescope, onboard the Fermi Gamma-ray Space Telescope, has detected the largest amount of gamma rays, in the 20 MeV 300 GeV energy range and electrons + positrons in the 7 GeV–1 TeV range. These impressive statistics allow one to perform a very sensitive indirect experimental search for dark matter. I will present the latest results on these searches.

LOWER LIMIT ON THE STRENGTH AND FILLING FACTOR OF EXTRAGALACTIC MAGNETIC FIELDS

High-energy photons from blazars can initiate electromagnetic pair cascades interacting with the extragalactic photon background. The charged component of such cascades is deflected and delayed by extragalactic magnetic fields (EGMFs), thereby reducing the observed point-like flux and potentially leading to multi-degree images in the GeV energy range. We calculate the fluence of 1ES 0229+200 as seen by Fermi-LAT for different EGMF profiles using a Monte Carlo simulation for the cascade development. The non-observation of 1ES 0229+200 by Fermi-LAT suggests that the EGMF fills at least 60% of space with fields stronger than G for lifetimes of TeV activity of yr. Thus, the (non-)observation of GeV extensions around TeV blazars probes the EGMF in voids and puts strong constraints on the origin of EGMFs: either EGMFs were generated in a space filling manner (e.g., primordially) or EGMFs produced locally (e.g., by galaxies) have to be efficiently transported to fill a significant volume fraction as, e.g., by galactic outflows.

Recent results on strangeness production from NA49

We present a summary of measurements of strange particle production performed by the experiment NA49 in inelastic p+p interactions, as well as semi-central C+C and Si+Si, central Pb+Pb and minimum bias Pb+Pb collisions in the energy range GeV. New results on π−, K+ and K− production in minimum bias Pb+Pb collisions at and 17.3 are shown. Furthermore the strangeness enhancement factor at GeV is presented and compared to the results from NA57 and STAR. The energy dependence of strange particle yields normalized to pion yields is presented. New data on ⟨K*(892)0⟩ production are shown at GeV. Furthermore we present the energy dependence of K/π and K/p fluctuations. The data are compared with model predictions.

The AGILE mission: The first 2 years

We summarize here the main highlights of the AGILE astrophysics mission. The satellite, launched in April 2007, is devoted to gamma-ray observations in the 30 MeV–30 GeV energy range, with simultaneous hard X-ray imaging in the 18–60 keV band, and optimal timing capabilities for the study of transient phenomena. The very large field of view (2.5 sr) of the gamma-ray imager coupled with the hard X-ray monitoring capability makes AGILE well suited to study Galactic and extragalactic sources, as well as GRBs and other fast transients. AGILE reaches its optimal performance near 100 MeV with good imaging and sensitivity. Gamma-ray and hard X-ray sources can be monitored 14 times a day, and an extensive database has been obtained for a variety of sources. We summarize here the breakthroughs and most important results obtained for several sources including microquasars and other Galactic compact objects (most notably, the discovery of gamma-ray emission above 100 MeV from Cygnus X-3), Supernova Remnants and pulsar wind nebulae, gamma-ray pulsars, a bright class of blazars (3C 454.3, TXS 0716+714, HB 1510-089, Mrk 421), short and long GRBs (including the remarkable short burst GRB 090510), and terrestrial gamma-ray flashes (TGFs).

Overview of the first AGILE catalog of high-confidence gamma-ray sources

AGILE is an Italian Space Agency mission launched in April 2007, devoted to γ ‐ray observations in the 30 MeV–50 GeV energy range, with simultaneous X-ray imaging capability in the 18–60 keV band. During its first year in orbit AGILE surveyed the γ ‐ray sky and detected many galactic and extragalactic sources. The first catalog of high-confidence γ ‐ray sources detected by AGILE during observations performed from July 9, 2007 to June 30, 2008, for energies greater than 100 MeV was recently published [1], and preliminary versions of the catalog were published on the AGILE Data Center webpage to allow AGILE Cycle-2 guest observers to benefit of the Catalog in the preparation of their proposals. We present here the main results of the final catalog, that includes 47 high-confidence sources, 21 of which are associated with confirmed or candidate pulsars, 13 with Blazars (7 FSRQ, 4 BL Lacs, 2 unknown type), 2 with HMXRBs, 2 with SNRs, 1 with a colliding-wind binary system, 8 with unidentified sources.

PRELIMINARY RESULTS ON η′ PHOTOPRODUCTION AT GRAAL

The γp → η′p reaction was studied near the threshold, in the 1.44 GeV > Eγ < 1.55 GeV energy range with the tagged photons of the former GRAAL experiment. The two neutral decays γγ(Γi/Γ = 2.10 ± 0.12%) and π0π0η(Γi/Γ = 20.7 ± 1.2%) were analized and preliminary results of the beam asymmetry were extracted together with the invariant masses.

Infrared study of astrophysical ice analogues irradiated by swift nickel ions

Water, carbon oxide, carbon dioxide, and ammonia ices are known to be pervasive constituents of the solar system and the interstellar medium. These ices and ice-covered surfaces are exposed to bombardment by energetic projectiles like photons, electrons, and ions. Laboratory experiments have been carried out to study the effects of such irradiation. However, there is a clear lack of information about the interaction of heavy ion components of solar/stellar wind and galactic cosmic rays (e.g. Fe) with ices in the keV to GeV energy range. The objective of this work is to study the effects produced in astrophysical ices by highly charged nickel ions at relatively high energy (∼50–500 MeV) in the electronic energy loss regime, and to compare them with those produced by protons, photons, and electrons. Our results for CO 2 and CO indicate that sputtering induced by heavy ions can be an important mechanism to desorb molecules in astrophysical environments.

DETECTION OF THE ENERGETIC PULSAR PSR B1509–58 AND ITS PULSAR WIND NEBULA IN MSH 15–52 USING THEFERMI-LARGE AREA TELESCOPE

We report the detection of high energy gamma-ray emission from the young and energetic pulsar PSR B1509$-$58 and its pulsar wind nebula (PWN) in the composite supernova remnant SNR G320.4-1.2 (aka MSH 15-52). Using 1 year of survey data with the Fermi-Large Area Telescope (LAT), we detected pulsations from PSR B1509-58 up to 1 GeV and extended gamma-ray emission above 1 GeV spatially coincident with the PWN. The pulsar light curve presents two peaks offset from the radio peak by phases 0.96 $\pm$ 0.01 and 0.33 $\pm$ 0.02. New constraining upper limits on the pulsar emission are derived below 1 GeV and confirm a severe spectral break at a few tens of MeV. The nebular spectrum in the 1 - 100 GeV energy range is well described by a power-law with a spectral index of (1.57 $\pm$ 0.17 $\pm$ 0.13) and a flux above 1 GeV of (2.91 $\pm$ 0.79 $\pm$ 1.35) 10^{-9} cm^{-2} s^{-1}. The first errors represent the statistical errors on the fit parameters, while the second ones are the systematic uncertainties. The LAT spectrum of the nebula connects nicely with Cherenkov observations, and indicates a spectral break between GeV and TeV energies.

OBSERVATIONS OF MILKY WAY DWARF SPHEROIDAL GALAXIES WITH THEFERMI-LARGE AREA TELESCOPE DETECTOR AND CONSTRAINTS ON DARK MATTER MODELS

We report on the observations of 14 dwarf spheroidal galaxies (dSphs) with the Fermi Gamma-Ray Space Telescope taken during the first 11 months of survey mode operations. The Fermi telescope, which is conducting an all-sky γ-ray survey in the 20 MeV to >300 GeV energy range, provides a new opportunity to test particle dark matter models through the expected γ-ray emission produced by pair annihilation of weakly interacting massive particles (WIMPs). Local Group dSphs, the largest galactic substructures predicted by the cold dark matter scenario, are attractive targets for such indirect searches for dark matter because they are nearby and among the most extreme dark matter dominated environments. No significant γ-ray emission was detected above 100 MeV from the candidate dwarf galaxies. We determine upper limits to the γ-ray flux assuming both power-law spectra and representative spectra from WIMP annihilation. The resulting integral flux above 100 MeV is constrained to be at a level below around 10−9 photons cm−2 s−1. Using recent stellar kinematic data, the γ-ray flux limits are combined with improved determinations of the dark matter density profile in eight of the 14 candidate dwarfs to place limits on the pair-annihilation cross section of WIMPs in several widely studied extensions of the standard model, including its supersymmetric extension and other models that received recent attention. With the present data, we are able to rule out large parts of the parameter space where the thermal relic density is below the observed cosmological dark matter density and WIMPs (neutralinos here) are dominantly produced non-thermally, e.g., in models where supersymmetry breaking occurs via anomaly mediation. The γ-ray limits presented here also constrain some WIMP models proposed to explain the Fermi and PAMELA e+e− data, including low-mass wino-like neutralinos and models with TeV masses pair annihilating into muon–antimuon pairs.

GeV emission from gamma-ray bursts: a radiative fireball?

We study the emission observed at energies greater than 100 MeV of 11 Gamma Ray Bursts (GRBs) detected by the Fermi/Large Area Telescope (LAT) until October 2009. The GeV emission has three main properties: (i) its duration is often longer than the duration of the softer emission detected by the Gamma Burst Monitor (GBM) onboard Fermi [this confirms earlier results from the Energetic Gamma-Ray Experiment Telescope (EGRET)]; (ii) its spectrum is consistent with F(v) propto v^(-1) and does not show strong spectral evolution; (iii) for the brightest bursts, the flux detected by the LAT decays as a power law with a typical slope: t^(-1.5). We argue that the observed >0.1 GeV flux can be interpreted as afterglow emission shortly following the start of the prompt phase emission as seen at smaller frequencies. The decay slope is what expected if the fireball emission is produced in the radiative regime, i.e. all dissipated energy is radiated away. We also argue that the detectability in the GeV energy range depends on the bulk Lorentz factor Gamma of the bursts, being strongly favoured in the case of large Gamma. This implies that the fraction of bursts detected at high energies corresponds to the fraction of bursts having the largest Gamma. The radiative interpretation can help to explain why the observed X-ray and optical afterglow energetics are much smaller than the energetics emitted during the prompt phase, despite the fact that the collision with the external medium should be more efficient than internal shocks in producing the radiation we see.