The energy spectrum of primary cosmic ray electrons from 2 GeV to 200 GeV

A balloon borne counter telescope with a gas Cerenkov counter is used to measure the energy of primary cosmic ray electrons between 2 and 200 GeV. Electrons are identified by the characteristic electron-photon shower which they produce in a 15 radiation length deep stack of high-Z material interleaved with scintillation counters. Calibrations with monoenergetic electrons up to 14 GeV and monoenergetic protons up to 28 GeV from accelerators are used to develop criteria to statistically separate electrons from proton induced events. The results from six balloon flights (total exposure time 63 hours) are combined to obtain the electron energy spectrum. Up to about 30 GeV the spectrum measured in this experiment can be directly checked with calibrations and agrees well with results from other experiments. Above this energy the flux reported here is somewhat higher than the determinations reported by most other authors. We do not attach significance to an apparent flattening of the energy spectrum above 50 GeV. There is no evidence for a steepening of the spectrum at energies below 200 GeV.Work supported in part by the National Aeronautics and Space Administration grant NGL 14-001-005.Also Department of Physics.NSF trainee (1965–1969).     

Reflectivity measurements in the vacuum ultraviolet wavelength range on technical surfaces for the Wolter I telescope on board the X-ray astronomy satellite ROSAT

The results of reflectivity measurements in the vacuum ultraviolet wavelength region (VUV) on technical surfaces are described which are used in the Wolter I-telescope on board the German X-ray astronomy satellite ROSAT.The materials investigated are the special iron-nickel alloy Invar and a carbon fibre compound (CFK).The centre connecting flange for the parabolic and hyperbolic mirror sections of the telescope is made of Invar. CFK is used for the thermal baffle in front of the telescope. It had to be checked whether the structure of the centre flange and the thermal baffle sufficiently suppress scattered ultraviolet radiation in order to avoid a substantial background level in the detectors which are located in the focal plane of the telescope. The detectors consist of two positional sensitive proportional counters (PSPC) with a spatial resolution of 0.5 arc min and an image converter with a resolution of a few arc sec. The detectors are mounted on a carrousel platform and are intended to be positioned alternatively in the focal plane.     

Position calibration methodology for scanning sky monitor for ASTROSAT

Scanning Sky Monitor (SSM) on ASTROSAT is an X-ray sky monitor which has a large Field of View (FOV) and scans the sky to detect and locate X-ray transient sources in the energy range 2 to 10 keV. Experiments are carried out to calibrate SSM detectors for position response and to verify the calibration constants derived. In this paper we discuss the methodology of position calibration of proportional counters for SSM and results from various experiments.     

Using the photons from the Crab Nebula seen by GLAST to calibrate MAGIC and the imaging air Cherenkov telescopes

In this article we discuss the possibility of using the observations by GLAST of standard gamma sources, as the Crab Nebula, to calibrate imaging air Cherenkov detectors, MAGIC in particular, and optimise their energy resolution. We show that at around 100 GeV the absolute energy calibration uncertainty of Cherenkov telescopes can be reduced to 10% by means of such cross-calibration procedure.     

Gamma–hadron separation methods for the VERITAS array of four imaging atmospheric Cherenkov telescopes

Ground-based arrays of imaging atmospheric Cherenkov telescopes have emerged as the most sensitive γ-ray detectors in the energy range of about 100 GeV and above. The strengths of these arrays are a very large effective collection area on the order of 10⁵ m², combined with excellent single photon angular and energy resolutions. The sensitivity of such detectors is limited by statistical fluctuations in the number of Cosmic-ray initiated air showers that resemble γ-ray air showers in many ways. In this paper, we study the performance of simple event reconstruction methods when applied to simulated data of the Very Energetic Radiation Imaging Telescope Array System (VERITAS) experiment. We review methods for reconstructing the arrival direction and the energy of the primary photons, and examine means to improve on their performance. For a software threshold energy of 300 GeV (100 GeV), the methods achieve point source angular and energy resolutions of σ_63% = 0.1° (0.2°) and σ_68% = 15% (22%), respectively. The main emphasis of the paper is the discussion of γ–hadron separation methods for the VERITAS experiment. We find that the information from several methods can be combined based on a likelihood ratio approach and the resulting algorithm achieves a γ–hadron suppression with a quality factor that is substantially higher than that achieved with the standard methods used so far.     

A search for very high energy bursts

Of great importance in distinguishing between models for gamma-ray bursts (GRBs) is the experimental determination of the highest energy gamma rays associated with bursts. The EGRET detection of a 15 GeV gamma ray indicates that the spectra of at least some bursts extend well beyond the several MeV limit of the BATSE detectors (Hurleyet al., 1994). The low expected flux means that the collecting area of the present generation of satellite-based detectors is too small to detect gamma rays much above this energy efficiently, and such searches are currently undertaken with ground based detectors. In this paper searches made for very high energy GRBs with a southern hemisphere air shower particle array are described.     

Gamma–hadron separation methods for the VERITAS array of four imaging atmospheric Cherenkov telescopes

Ground-based arrays of imaging atmospheric Cherenkov telescopes have emerged as the most sensitive γ-ray detectors in the energy range of about 100 GeV and above. The strengths of these arrays are a very large effective collection area on the order of 10⁵ m², combined with excellent single photon angular and energy resolutions. The sensitivity of such detectors is limited by statistical fluctuations in the number of Cosmic-ray initiated air showers that resemble γ-ray air showers in many ways. In this paper, we study the performance of simple event reconstruction methods when applied to simulated data of the Very Energetic Radiation Imaging Telescope Array System (VERITAS) experiment. We review methods for reconstructing the arrival direction and the energy of the primary photons, and examine means to improve on their performance. For a software threshold energy of 300 GeV (100 GeV), the methods achieve point source angular and energy resolutions of σ_63% = 0.1° (0.2°) and σ_68% = 15% (22%), respectively. The main emphasis of the paper is the discussion of γ–hadron separation methods for the VERITAS experiment. We find that the information from several methods can be combined based on a likelihood ratio approach and the resulting algorithm achieves a γ–hadron suppression with a quality factor that is substantially higher than that achieved with the standard methods used so far.     

Detection of atmospheric Cherenkov radiation using solar heliostat mirrors

There is considerable interest world-wide in developing large area atmospheric Cherenkov detectors for ground-based gamma-ray astronomy. This interest stems, in large part, from the fact that the gamma-ray energy region between 20 and 250 GeV is unexplored by any experiment. Atmospheric Cherenkov detectors offer a possible way to explore this region, but large photon collection areas are needed to achieve low energy thresholds. We are developing an experiment using the heliostat mirrors of a solar power plant as the primary collecting element. As part of this development, we built a detector using four heliostat mirrors, a secondary Fresnel lens, and a fast photon detection system. In November 1994, we used this detector to record atmospheric Cherenkov radiation produced by cosmic ray particles showering in the atmosphere. The detected rate of cosmic ray events was consistent with an energy threshold near 1 TeV. The data presented here represent the first detection of atmospheric Cherenkov radiation using solar heliostats viewed from a central tower.     

宇宙线通过正比管径迹长度的模拟计算

高能天体物理观测中,宇宙线带电粒子通过探测器丢失的能量常是产生探测器本底信号的重要来源。宇宙线产生的信号与它通过探测器的径迹长度和探测器大小、形状有关。因气球X射线天文观测和γ射线暴观测的需要,空间天文实验室研制了若干种正比计数器,为此我们进行了宇宙线通过正比管径迹长度的模拟计算,它是整个设计工作中的一部分。     

Gamma rays from the Galactic Centre region: A review

During the last decades, increasingly precise astronomical observations of the Galactic Centre (GC) region at radio, infrared, and X-ray wavelengths laid the foundations to a detailed understanding of the high energy astroparticle physics of this most remarkable location in the Galaxy. Recently, observations of this region in high energy (HE, 10 MeV–100 GeV) and very high energy (VHE, > 100 GeV) γ-rays added important insights to the emerging picture of the Galactic nucleus as a most violent and active region where acceleration of particles to very high energies – possibly up to a PeV – and their transport can be studied in great detail. Moreover, the inner Galaxy is believed to host large concentrations of dark matter (DM), and is therefore one of the prime targets for the indirect search for γ-rays from annihilating or decaying dark matter particles. In this article, the current understanding of the γ-ray emission emanating from the GC is summarised and the results of recent DM searches in HE and VHE γ-rays are reviewed.     

A comparison of spectral reduction techniques in X-Ray astronomy

We report the results of a numerical investigation of three methods of cosmic X-ray spectral reduction, with an emphasis on the apodization technique of Dolan (1972). The study is carried out in the energy range 10–100 keV on pulse height distributions which were synthesized from simple X-ray source spectra with predetermined parameters. The spectral response function used was that of a balloon-borne, large area, xenon-filled proportional counter; however, we believe that our results are generally relevant to other non-dispersive systems such as scintillators and low energy (1–10 keV) proportional counters. We agree that the ill-conditioned energy resolution matrix cannot be inverted using standard procedures without propagating unacceptable errors. The apodization solution was investigated as a function of counter resolution, fluorescence escape probability, extent of energy window, number of pulse height channels, dataS/N ratio, and the so-called apodization instrument factor. We conclude that in most circumstances apodization should be the preferred reduction technique, but that the present widely and improperly used minimum –x ² method may be useful as the final step in obtaining refined spectral parameters estimates.     

The X-ray astronomy satellite “ASCA”

ASCA (ASTRO-D), the fourth X-ray astronomy satellite of ISAS, was successfully launched on February 20, 1993. It carries nested thin-foil X-ray mirrors providing a large effective area over a wide energy range up to 12 keV. A set of CCD cameras and imaging gas scintillation proportional counters are placed on the focal plane.ASCA is a high-throughput imaging and spectroscopic X-ray observatory with these instruments.     

The HEAO-3 Cosmic Ray Isotope spectrometer

This paper describes the Cosmic Ray Isotope instrument launched aboard the HEAO-3 satellite on September 20, 1979. The primary purpose of the experiment is to measure the isotopic composition of cosmic ray nuclei from Be-7 to Fe-58 over the energy range 0.5 to 7 GeV/nucleon. In addition charge spectra will be measured between beryllium and tin over the energy range 0.5 to 25 GeV/nucleon. The charge and isotope abundances measured by the experiment provide essential information needed to further our understanding of the origin and propagation of high energy cosmic rays. The instrument consists of 5 Cerenkov counters, a 4 element neon flash tube hodoscope and a time-of-flight system. The determination of charge and energy for each particle is based on the multiple Cerenkov technique and the mass determination will be based upon a statistical analysis of particle trajectories in the geomagnetic field.Representing the Saclay-Copenhagen CollaborationOriginally submitted to the journalSpace Science Instrumentation.The Saclay-Copenhangen Collaboration consists of the authors and the following members.     

First operation of bulk micromegas in low pressure negative ion drift gas mixtures for dark matter searches

A bulk micromegas micropattern charge readout device has, for the first time, been operated at room temperature in low pressure carbon disulphide vapour. This is a key step opening prospects for use of micromegas readout for large volume negative ion time projection chambers (TPCs) without magnets, such as proposed for directional dark matter detectors and other rare event applications. The dependence of the gain on the amplification field, pressure and drift field has been evaluated. For the available gap size of 75 μm a maximum gain of 1300 ± 120 was achieved in 40 torr vapour with an energy resolution of 22% for 5.9 keV ⁵⁵Fe X-rays. From a fit to the data, the Townsend coefficient gas parameters A and B have been derived. Operation has also been successfully achieved in xenon:carbon disulphide blends over a range of partial and total pressures. A gain of 890 ± 130 at an energy resolution of 35% has been recorded for a 1:1 blend at a total pressure of 80 torr. Possible improvements are discussed in the context of operation in directional dark matter TPCs as a replacement for multi-wire proportional counters.     

Observation of cosmic soft X-rays

Cosmic soft X-rays in the energy range between 0.14 and 7 keV were observed with thin polypropylene window proportional counters on board a sounding rocket. The field of view crossed the galactic plane in the Cygnus-Cassiopeia region at a large angle and reached the galactic latitudes of –55° and +30°. Referring also to the result with Be window counters, we obtained the energy spectrum of Cyg XR-2, the flux from the Cas A region and the distribution of the intensity of diffuse X-rays over the scanned region. The turn-over of the Cyg XR-2 spectrum at about 1 keV indicates that the distance of the Cyg XR-2 source lies between 600 and 800 pc, if the turn-over is due entirely to interstellar absorption. The flux from the Cas A region is obtained as 0.23±0.05 photons cm^–2 sec^–1 in the energy range between 1.1 and 4.1 keV. The intensity of diffuse soft X-rays depends on the galactic latitude more weakly than expected from the interstellar absorption of extragalactic X-rays and shows asymmetry with respect to the galactic equator, thus suggesting a contribution of galactic X-rays. The spectrum of extragalactic X-rays is approximately represented by a power lawE ^–1.8.     

The potential of the ground based arrays of imaging atmospheric Cherenkov telescopes. II. Gamma ray flux sensitivities

We discuss the capability of ‘100 GeV’ class imaging atmospheric Cherenkov telescope (IACT) arrays as future powerful instruments of ground-based gamma-ray astronomy. It is assumed that the array is gathered from individually triggered quadrangular 4-IACT ‘cells’ with a linear size of about 100 m. The multi-cell concept allows coverage of large detection areas economically, and at the same time the effective exploitation of the stereoscopic approach of determination of the shower parameters using information obtained by several IACTs simultaneously. Determination of arrival directions of γ-ray primaries on an event-by-event basis with accuracy δθ ≤ 0.1° combined with high suppression efficiency (at both the hardware and software levels) of the background hadronic showers by a factor of ≈ 10³, and large, up to 1 km² collection areas, can provide minimum detectable energy fluxes of ≥ 100 GeV γ-rays from point sources down to 10⁻¹³ erg/cm² s which is about 3 orders of magnitude lower than the current sensitivities achieved by the satellite-borne detectors at MeV and GeV energies. High sensitivities of multi-IACT arrays would partially compensate the limited efficiency of the technique for all-sky surveys, as well as allow study of moderately extended (≤ 1°) γ-ray sources. IACT arrays with minimum detectable fluence of ≥ 100 GeV γ-rays S_γ < 10⁻⁸ erg/cm² are well suited for effective exploration of highly sporadic nonthermal phenomena from different classes of astrophysical objects on time-scales from ≤ 1 s to several minutes.     

A study of secondary cosmic ray flux variation during the annular eclipse of 15 January 2010 at Rameswaram, India

The gamma ray flux was measured during the annular solar eclipse on January 15, 2010 at Rameswaram, India using NaI (Tl) scintillator detectors and the variation in charged particles and gamma rays was monitored using Geiger Mu¨ller (GM) counters. The gamma ray flux variation was studied in energy range of 0.1–3.5 MeV. Weather parameters (temperature and humidity) were continuously recorded throughout the duration of the eclipse at the site and correlation between gamma ray flux and weather parameters was examined. Analysis of the secondary cosmic ray flux using Fast Fourier Transform (FFT) was carried out to study the impact of the eclipse on the flux modulation. An overall decrease in flux was observed by both GM counters and scintillator detectors. A relative enhancement observed for short time during the eclipse which could be associated with the presence of counter electrojet observed at Rameswaram. This is suggestive of an increase in secondary cosmic ray flux at the geomagnetic equator during every counter electrojet due to decrease in geomagnetic rigidity.     

Observation of the energy spectrum of cosmic diffuse X-rays in the energy range 20 keV-4 MeV

Balloon observations of the cosmic diffuse component of hard X-rays were conducted with two independent directional counters in two energy bands, from 20 keV to 120 keV and from 90 keV to 4 MeV. The build-up effect of primary X-rays and the altitude dependence of atmospheric X-rays were properly taken into account in the analysis of the growth curves. These two experiments gave consistent results in the overlapping energy region. If the differential energy spectrum of the photon flux is represented by a power lawE ^?α, the value of α is 2.3 up to 100 keV, gradually increases to 2.8 at about 500 keV, and decreases to 2.0 thereabove. The spectrum above 300 keV is in parallel to the Apollo-15 spectrum, whereas the absolute intensity is somewhat smaller. The shape of the spectrum suggests the necessity of a multi-component theory on the origin of cosmic diffuse X-rays.     

High energy γ-ray emission from compact galactic sources in the context of observations with the next generation Cherenkov Telescope Arrays

The observational progress in the γ-ray astronomy in the last few years has led to the discovery of more than a thousand sources at GeV energies and more than a hundred sources at TeV energies. A few different classes of compact objects in the Galaxy have been established. They show many unexpected features at high energies the physics of which remains mainly unknown. At present it is clear that detailed investigation of these new phenomena can be performed only with the technical equipment which offer an order of magnitude better sensitivity, and a few times better energy, angular and time resolution in the broad energy range staring from a few tens of GeV up to a few hundreds TeV. Such facilities can be realized by the next generation of instruments such as the planned Cherenkov Telescope Array (CTA).The aim of this report is to summarize up to date observational results on the compact galactic sources in the GeV–TeV γ-ray energy range, discuss their theoretical implications, and indicate which hypothesis considered at present might be verified with the next generation of telescopes. We point out which of the observational features of the γ-ray sources are important to investigate with special care with the planned CTA in order to throw new light on physical processes involved. Their knowledge should finally allow us to answer the question on the origin of energetic particles in our Galaxy.