117810362
TeV Gamma-Ray Observations of the Cataclysmic Variable AE Aqr
17729334
Predictions of gamma-ray emission from globular cluster millisecond pulsars above 100 MeV
The recent Fermi detection of the globular cluster (GC) 47 Tucanae highlighted the importance of modeling collective gamma-ray emission of millisecond pulsars (MSPs) in GCs. Steady flux from such populations is also expected in the very high energy domain covered by ground-based Cherenkov telescopes. We present pulsed curvature radiation (CR) as well as unpulsed inverse Compton (IC) calculations for an ensemble of MSPs in the GCs 47 Tucanae and Terzan 5. We demonstrate that the CR from these GCs should be easily detectable for Fermi, while constraints on the total number of MSPs and the nebular B-field may be derived using the IC flux components.
16108343
Are Galactic Gamma-Ray Bursters the Main Source of Hadronic Non-Solar Cosmic Rays at all Energies?
We propose a new hypothesis for the origin of non-solar hadronic cosmic rays (CRs) at all energies: Highly relativistic, narrowly collimated jets from the birth or collapse of neutron stars (NSs) in our Galaxy accelerate ambient disk and halo matter to CR energies and disperse it in ``hot spots'' which they form when they stop in the Galactic halo. Such events - ``Galactic Gamma-Ray Bursters'' (GGRBs) - are proposed to cause cosmological gamma-ray bursts (GRBs) in other galaxies when their beamed radiation happens to point in our direction. Our hypothesis naturally explains some observations which are difficult to understand with the currently popular ideas about CR origin - e.g. the small Galacto-centric gradient of the cosmic-ray density and the absence of the Greisen-Zatsepin-Kuzmin cutoff. Our idea stands or falls with the existence of the ``hot spots'' (``GGRB remnants'') in the Galactic halo. We discuss their expected observational signatures and find that they could appear as EGRET unidentified high-latitude sources.
118199686
Modelling the IR de-absorbed gamma-ray spectra of TeV BL Lacs
1. Abstract A sample of the BL Lac objects detected so far in TeV γ-rays consists of four well established sources, in particular Mkn 501, Mkn 421, 1ES 1426+428, and 1ES 1959+650. The energy spectra of these objects at TeV energies show the steepening in the spectral slope, which can be attributed to the γ-ray absorption onto extra-galactic infra-red (IR) background light. Based on the empirically based model of the IR spectral energy distribution (SED) we have unfolded the intrinsic spectra of two BL Lac objects: Mkn 501 and Mkn 421 and modeled the TeV γ-ray emission in the synchrotron-self Compton (SSC) scenario.
9619588
HESS J 1825-137 : A pulsar wind nebula associated with PSR B 1823-13 ?
HESS J1825–137 was detected with a significance of 8.1 σ in the Galactic Plane survey conducted with the H.E.S.S. instrument in 2004. Both HESS J1825–137 and the X-ray pulsar wind nebula G18.0–0.7 (associated with the Vela-like pulsar PSR B1823–13) are offset south of the pulsar, which may be the result of the SNR expanding into an inhomogeneous medium. The TeV size (∼ 35 pc, for a distance of 4 kpc) is ∼ 6 times larger than the X-ray size, which may be the result of propagation effects as a result of the longer lifetime of TeV emitting electrons, compared to the relatively short lifetime of keV synchrotron emitting electrons. The TeV photon spectral index of ∼ 2.4 can also be related to the extended PWN X-ray synchrotron photon index of ∼ 2.3, if this spectrum is dominated by synchrotron cooling. The remaining problem is the anomalously large size of the pulsar wind nebula (PWN): the SNR shell is not seen in radio or X-rays, and for a SNR shell expanding in the Sedov-Taylor phase, the expected shell radius is expected to be ≤ 80 pc, implying a ratio of PWN to SNR radius ≥ 0.5, whereas a ratio of ∼ 0.25 is expected from model calculations.
121428693
Search for TeV gamma-ray emission from binary radio pulsars
118228975
Mass loss rates in the Hertzsprung-Russell diagram
Discussion des donnees de la litterature concernant les pertes de masse de 271 etoiles de types O o M de population I, etablissement d'une relation M˙(T eff , L/L ○. ) representant la perte de masse-M˙ comme fonction de la temperature effective et de la luminosite et discussion de la precision de la procedure d'ajustement
120209735
Electroproduction of neutral pions on the proton
Abstract The double-differential coincidence cross section for the reaction 1 H(e,e′π 0 )p has been measured at Q 2 = 0.1 (GeV/ c ) 2 for a range in the invariant energy W of 1 to 14 MeV above threshold in order to determine the s-wave multipoles E 0+ and L 0+ . The experiment was performed with a 525 MeV electron beam of the Amsterdam Pulse Stretcher and a cryogenic hydrogen target. The scattered electron and the recoiling proton were detected in two high-resolution magnetic spectrometers. By using a recent LET prediction for the relevant combinations of p-wave multipoles, values for E 0+ and L 0+ were extracted from the cos ϑ π ∗ and cos φ π ∗ dependent terms in the cross section. The data are compared to calculations from Chiral Perturbation Theory and from several Lagrangian models. All models give a fair to good description of L 0+ . ChPT gives also a good description of E 0+ , but the Lagrangian models tend to underestimate its value. The data for the angle-independent part of the cross section indicate that the value for the 2 M 1+ + M 1− combination of p-wave multipoles is overestimated by a recent ChPT prediction.
120287769
Longitudinally polarized electrons in a storage ring below 1 GeV
We report on the results of studies of the longitudinal electron polarization in the AmPS storage ring at NIKHEF. The ring was operated using a partial Siberian snake at the first magic energy, and a full Siberian snake between 440 MeV and 720 MeV. We have investigated the effect of high beam currents in the ring, and found that some of the electron polarization is lost if the beam current becomes larger than ≈120 mA.
119220108
Performance of the Two Aerogel Cherenkov Detectors of the JLab Hall A Hadron Spectrometer
We report on the design and commissioning of two silica aerogel Cherenkov detectors with different refractive indices. In particular, extraordinary performance in terms of the number of detected photoelectrons was achieved through an appropriate choice of PMT type and reflector, along with some design considerations. After four years of operation, the number of detected photoelectrons was found to be noticeably reduced in both detectors as a result of contamination, yellowing, of the aerogel material. Along with the details of the set-up, we illustrate the characteristics of the detectors during different time periods and the probable causes of the contamination. In particular we show that the replacement of the contaminated aerogel and parts of the reflecting material has almost restored the initial performance of the detectors.
3095859
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%/\sqrt(E{\gamma} [GeV]). Features of both the detector design and its performance in the high luminosity environment during the experiment are presented.