Dark Matter Particle Explorer and Its First Results

The Dark Matter Particle Explorer (DAMPE) is China's first astronomical satellite dedicated to the indirect detection of dark matter particles and the study of high-energy astrophysics. It can measure high-energy electrons and gamma-rays up to 10 TeV with unprecedentedly high energy resolution and low background. Cosmic ray nuclei up to 100 TeV can also be measured. DAMPE was launched on December 17, 2015, and has been operating smoothly in space for more than two years since then. The first results about the precise measurements of the electron plus positron spectrum between 25 GeV and 4.6 TeV have been reported.      

Direct dark matter searches with CDMS and XENON

The cryogenic dark matter search (CDMS) and XENON experiments aim to directly detect dark matter in the form of weakly interacting massive particles (WIMPs) via their elastic scattering on the target nuclei. The experiments use different techniques to suppress background event rates to the minimum, and at the same time, to achieve a high WIMP detection rate. The operation of cryogenic Ge and Si crystals of the CDMS-II experiment in the Soudan mine reported spectrum-weighted exposures of 34 (12) kg-d for the Ge (Si) targets after cuts, over the recoil energies 10–100 keV for a WIMP mass of 60 GeV/c². It gives an upper limit (90% C.L.) of spin-independent WIMP-nucleon cross-section at 1.6 × 10⁻⁴³ cm² for a WIMP mass of 60 GeV/c², starting to constrain predications in supersymmetry models. The two-phase xenon detector of the XENON10 experiment is currently taking data in the Gran Sasso underground lab and promising preliminary results were recently reported. Both experiments are expected to increase their WIMP sensitivity by a one order of magnitude in the scheduled science runs for 2007.     

Launch and commissioning of the PAMELA experiment on board the Resurs-DK1 satellite

PAMELA is a satellite borne experiment designed to study with great accuracy cosmic rays of galactic, solar, and trapped nature in a wide energy range (protons: 80 MeV–700 GeV, electrons 50 MeV–400 GeV). Main objective is the study of the antimatter component: antiprotons (80 MeV–190 GeV), positrons (50 MeV–270 GeV) and search for antimatter (with a precision of the order of 10⁻⁸). The experiment, housed on board the Russian Resurs-DK1 satellite, was launched on June, 15th 2006 in a 350 × 600 km orbit with an inclination of 70°. The detector consists of a permanent magnet spectrometer core to provide rigidity and charge sign information, a Time-of-Flight system for velocity and charge information, a silicon–tungsten calorimeter and a neutron detector for lepton/hadron identification. An anticounter system is used off-line to reject false triggers coming from the satellite. In self-trigger mode the calorimeter, the neutron detector and a shower tail catcher are capable of an independent measure of the lepton (e⁺ + e⁻) component up to 2 TeV. In this work we focus on the first months of operations of the experiment during the commissioning phase.     

Cosmic-ray electron spectrum above 100 GeV from PPB-BETS experiment in Antarctica

Cosmic-ray electrons have been observed in the energy region from 10 GeV to 1 TeV with the PPB-BETS by a long duration balloon flight using a Polar Patrol Balloon (PPB) in Antarctica. The observation was carried out for 13 days at an average altitude of 35 km in January 2004. The PPB-BETS detector is an imaging calorimeter composed of scintillating-fiber belts and plastic scintillators inserted between lead plates. In the study of cosmic-ray electrons, there have been some suggestions that high-energy electrons above 100 GeV are a powerful probe to identify nearby cosmic-ray sources and search for particle dark matter. In this paper, we present the energy spectrum of cosmic-ray electrons in the energy range from 100 GeV to 1 TeV at the top of atmosphere, and compare our spectrum with the results from other experiments.     

The PAMELA experiment: A space-borne observatory for heliospheric phenomena

PAMELA is a multi-purpose apparatus composed of a series of scintillator counters arranged at the extremities of a permanent magnet spectrometer to provide charge, time-of-flight and rigidity information. Lepton/hadron identification is performed by a silicon–tungsten calorimeter and a Neutron detector placed at the bottom of the device. An Anticounter system is used offline to reject false triggers coming from the satellite. The device was put into orbit on June 15th 2006 in a pressurized container on board the Russian Resurs-DK1 satellite. The satellite is flying along a high inclination (70°), low Earth orbit (350–600 km), allowing to perform measurements in different points and conditions of the geomagnetosphere. PAMELA main goal is a precise measurement of the antimatter ( 80 MeV–190 GeV, e⁺ 50 MeV–270 GeV) and matter (p 80–700 GeV, e⁻ 50 MeV–400 GeV) component of the galactic cosmic rays. In this paper we focus on the capabilites of observations of heliospheric cosmic rays: trapped and semi-trapped particles in the proton and electron belts, solar particle events, Jovian electrons will be studied in the three years of expected mission.     

Dark Matter searches with GLAST

The Gamma-ray Large Area Space Telescope (GLAST), scheduled to be launched in fall 2007, is the next generation satellite for high-energy gamma-ray astronomy. The Large Area Telescope (LAT), GLAST main instrument, with a wide field of view (>2 sr), a large effective area (>8000 cm² at 1 GeV) and 20 MeV–300 GeV energy range, will provide excellent high energy gamma-ray observations for Dark Matter searches. In this paper we examine the potential of the LAT to detect gamma-rays coming from WIMPS annihilation in the context of supersymmetry. As an example, two search regions are investigated: the galactic center and the galactic satellites.     

Status of the GAMMA-400 project

The preliminary design of the new space gamma-ray telescope GAMMA-400 for the energy range 100 MeV–3 TeV is presented. The angular resolution of the instrument, 1–2° at E_γ ∼ 100 MeV and ∼0.01° at E_γ > 100 GeV, its energy resolution ∼1% at E_γ > 100 GeV, and the proton rejection factor ∼10⁶ are optimized to address a broad range of science topics, such as search for signatures of dark matter, studies of Galactic and extragalactic gamma-ray sources, Galactic and extragalactic diffuse emission, gamma-ray bursts, as well as high-precision measurements of spectra of cosmic-ray electrons, positrons, and nuclei.     

High-energy cosmic-ray electrons in the Galaxy

The intensity of cosmic-ray electrons is only ∼1% of the protons at 10 GeV, and decreases very rapidly with energy to be ∼0.1% of protons at 1 TeV. Nevertheless, electrons in cosmic-rays have unique features, complementary to all other cosmic-ray nucleonic components, because they enable us to find the origins of cosmic-rays and the properties of their propagation mechanisms in the Galaxy. High-energy electrons lose energy by synchrotron and inverse Compton processes during the propagation in the Galaxy. Since the energy loss rate by these processes is proportional to the square of energy, TeV electrons accelerated in the sources at distances larger than ∼1 kpc, or ages greater than a few 10⁵ yr, cannot reach the solar system. This suggests that some nearby sources leave unique signatures in the form of identifiable structures in the energy spectrum of TeV electrons, and show increases of the flux towards the sources. In this paper, I review the past observations of high-energy cosmic-ray electrons and discuss their astrophysical significance.     

Study of correlations between waves and particle fluxes measured on board the DEMETER satellite

The topic of relativistic electron dynamics in the outer radiation belt has received considerable attention for many years. Nevertheless, the problem of understanding the physical phenomenon involved is far from being resolved. In this paper, we use DEMETER observations to examine the variations of the energetic electron fluxes and ELF/VLF wave intensities in the inner magnetosphere during the intense 8 November 2004 magnetic storm. Electron flux spectra and associated wave intensity spectra are analysed throughout the magnetic storm and common characteristics or differences to other storm events are retained. The overall objective of this study is to identify and derive parameters that are relevant for particle flux modelling; the time constant characterizing the persistent decay after particle enhancement was found to be one of these important model parameters.The analysis of the 8 November 2004 event reveals that for L-shell parameter higher than 4, an electron flux dropout is observed during the storm’s main phase for electrons in the energy range 0.1–1 MeV, as has been reported from other measurements. Characteristic wave spectra accompanying this phase are analysed. They show a typical enhancement in the frequency range 0.3–10 kHz at onset for all L-shell values under consideration (2 < L < 5). During the first stage of the recovery phase, the electron fluxes are increased to a level higher than the pre-storm level, whereas the level of wave intensity in the frequency range observed below 300 Hz is at its highest. In the second stage, the particle flux decrease goes hand in hand with a global wave activity decline, the relaxation time of the latter being smaller than the former’s one. In some other cases, long-lasting electron enhancement associated with constant wave activity has been observed during this latter stage. For the above mentioned storm, while at low L values the decay time constants are higher for low energy electrons than for high energy electrons, this order is reversed at high L values. At about L = 3.6 the time constant is independent of electron energy.     

PAMELA observational capabilities of Jovian electrons

PAMELA is a satellite-borne experiment that has been launched on June 15th, 2006. It is designed to make long duration measurements of cosmic radiation over an extended energy range. Specifically, PAMELA is able to measure the cosmic ray antiproton and positron spectra over the largest energy range ever achieved and will search for antinuclei with unprecedented sensitivity. Furthermore, it will measure the light nuclear component of cosmic rays and investigate phenomena connected with solar and earth physics. The apparatus consists of: a time of flight system, a magnetic spectrometer, an electromagnetic imaging calorimeter, a shower tail catcher scintillator, a neutron detector and an anticoincidence system. In this work a study of the PAMELA capabilities to detect electrons is presented. The Jovian magnetosphere is a powerful accelerator of electrons up to several tens of MeV as observed at first by Pioneer 10 spacecraft (1973). The propagation of Jovian electrons to Earth is affected by modulation due to Corotating Interaction Regions (CIR). Their flux at Earth is, moreover, modulated because every 13 months Earth and Jupiter are aligned along the average direction of the Parker spiral of the Interplanetary Magnetic Field.PAMELA will be able to measure the high energy tail of the Jovian electrons in the energy range from 50 up to 130 MeV. Moreover, it will be possible to extract the Jovian component reaccelerated at the solar wind termination shock (above 130 MeV up to 2 GeV) from the galactic flux.     

Propagation of cosmic-ray electrons in the Galaxy

We formulate the global propagation model of cosmic-ray electrons including the source region, which is currently considered to be supernova remnants (SNRs). The model is characterized by the escape rate of electrons from SNRs into the interstellar space. It becomes clear that the energy index of the escape rate influences the high energy side of the interstellar spectrum and makes it possible to explain the observed data up to 2 TeV in the case of source spectral index smaller than 2.2 that is expected from the radio spectrum in SNRs. The escape lifetime of electrons in SNRs is also discussed by using the ratio of the radio flux in two regions: SNRs and the Galaxy. The result shows the mean lifetime in SNRs of ∼10⁴ yr around 1 GeV, which corresponds to the SNR age in the Sedov phase.     

Propagation and origin of ultra high-energy cosmic rays

Propagation of UHE protons through CMB radiation leaves the imprint on energy spectrum in the form of Greisen–Zatsepin–Kuzmin (GZK) cutoff, bump (pile-up protons) and dip. The dip is a feature in energy range 1 × 10¹⁸–4 × 10¹⁹ eV, caused by electron–positron pair production on CMB photons. Calculated for power-law generation spectrum with index γ_g = 2.7, the shape of the dip is confirmed with high accuracy by data of Akeno-AGASA, HiRes, Yakutsk and Fly’s Eye detectors. The predicted shape of the dip is robust: it is valid for the rectilinear and diffusive propagation, for different discreteness in the source distribution, for local source overdensity, deficit, etc. This property of the dip allows us to use it for energy calibration of the detectors. The energy shift λ for each detector is determined by minimum χ² in comparison of observed and calculated dip. After this energy calibration the absolute fluxes, measured by AGASA, HiRes and Yakutsk detectors remarkably coincide in energy region 1 × 10¹⁸–1 × 10²⁰ eV. Below the characteristic energy E_c ≈ 1 × 10¹⁸ eV the spectrum of the dip flattens for both diffusive and rectilinear propagation, and more steep galactic spectrum becomes dominant at E < E_c. The energy of transition E_tr < E_c approximately coincides with the position of the second knee E_2kn, observed in the cosmic ray spectrum. The dip-induced transition from galactic to extragalactic cosmic rays at the second knee is compared with traditional model of transition at ankle, the feature observed at energy 1 × 10¹⁹ eV.     

High energy radiation from the direction of the galactic black hole Sgr A

X-ray observations indicate that the Galactic black hole Sgr A^∗ is inactive now, however, we suggest that Sgr A^∗ can become active when a captured star is tidally disrupted and matter is accreted into the black hole. Consequently the Galactic black hole could be a powerful source of relativistic protons with a characteristic energy ∼10⁵² erg per capture. The diffuse GeV and TeV γ-rays emitted in the direction of the Galactic Center (GC) are the direct consequences of p–p collisions of such relativistic protons ejected by very recent capture events occurred ?10⁵ yr ago. On the other hand, the extended electron-positron annihilation line emission observed from GC is a phenomenon related to a large population of thermalized positrons, which are produced, cooled down and accumulated through hundreds of past capture events during a period of ∼10⁷ yr. In addition to explaining GeV, TeV and 511 keV annihilation emissions we also estimate the photon flux of several MeV resulting from in-flight annihilation process.     

Simulation of ASTROD I test mass charging due to solar energetic particles and interplanetary electrons

As ASTROD I travels through space, its test mass will accrue charge due to exposure of the spacecraft to high-energy particles. This test mass charge will result in Coulomb forces between the test mass and the surrounding electrodes. In earlier work, we have used the GEANT 4 toolkit to simulate charging of the ASTROD test mass due to cosmic-ray protons of energies between 0.1 and 1000 GeV at solar maximum and at solar minimum. Here we use GEANT 4 to simulate the charging process due to solar energetic particle events and interplanetary electrons. We then estimate the test mass acceleration noise due to these fluxes. The predicted charging rates range from 2247 e⁺/s to 47,055 e⁺/s, at peak intensity, for the four largest SEP events in September and October 1989. Although the noise due to charging exceeds the ASTROD I budget for the two larger events, it can be suppressed through continuous discharging. The acceleration noise during the two small events is well below the design target. The charging rate of the ASTROD I test mass due to interplanetary electrons in this simulation is about −11% of the cosmic-ray protons at solar minimum, and over −37% at solar maximum. In addition to the Monte Carlo uncertainty, an error of ±30% in the net charging rates should be added to account for uncertainties in the spectra, physics models and geometry implementations.     

Gamma ray astrophysics and signatures of axion-like particles

We propose that axion-like particles (ALPs) with a two-photon vertex, consistent with all astrophysical and laboratory bounds, may lead to effects in the spectra of high-energy gamma-ray sources detectable by satellite or ground-based telescopes. We discuss two kinds of signatures: (i) a peculiar spectral depletion due to gamma rays being converted into ALPs in the magnetic fields of efficient astrophysical accelerators according to the “Hillas criterion”, such as jets of active galactic nuclei or hot spots of radio galaxies; (ii) an appearance of otherwise invisible sources in the GeV or TeV sky due to back-conversion of an ALP flux (associated with gamma-ray emitters suffering some attenuation) in the magnetic field of the Milky Way. These two mechanisms might also provide an exotic way to avoid the exponential cutoff of very high energy gamma-rays expected due to the pair production onto the extragalactic background light.     

Equatorial F-region vertical ion drifts during quiet solar maximum

Median values of ionosonde h′F data acquired at Ibadan (Geographic:7.4°N, 3.9°E, Magnetic: dip 6°S, and magnetic declination, 3°W), Nigeria, West Africa, have been used to determine vertical ion drift (electric field) characteristics in the postsunset ionosphere in the African region during a time of high solar activity (average F_10.7 −208). The database spans from January and December 1958 during the era of International Geophysical Year (IGY) for geomagnetic quiet conditions. Bimonthly averaged diurnal variations patterns are very similar, but differ significantly in magnitude and in the evening reversal times. Also, monthly variations of F-region vertical ion drift reversal times inferred from the time of h′F maximum indicates early reversal during equinoxes and December solstice months except for the month of April. Late reversal is observed during the June solstice months. The equatorial evening prereversal enhancement in vertical ion drift (V_zp) occurs largely near 1900 LT with typical values 20–45 m/s. Comparison of Ibadan ionosonde V_zp with the values of prereversal peak velocity reported for Jicamarca (South America), Kodaikanal (India), and Scherliess and Fejer global model show considerable disparity. The changes of postsunset peak in virtual height of F-layer (h′F_P) with prereversal velocity peak V_zp are anti-correlated. Investigation of solar effects on monthly values of V_zp and h′F_P revealed that these parameters are independent of monthly averaged solar flux intensity during quiet-time sunspot maximum conditions.     

以载荷为中心的暗物质探测卫星机电热一体化设计

暗物质粒子探测卫星是中国第一颗空间高能探测卫星,用于实现5GeV~10TeV大动态范围高能宇宙线（电子、正电子、伽马射线等）能谱测量.卫星有效载荷包括BGO量能器、硅阵列探测器、塑闪阵列探测器和中子探测器,是目前中国发射的载荷比最大的卫星.本文介绍了卫星相关技术方案,包括技术指标、轨道方案、工作模式及系统组成等,突出了其以载荷为中心的机电热一体化设计特点.      

Dark Matter Particle Explorer:The First Chinese Cosmic Ray and Hard γ-ray Detector in Space

The Dark Matter Particle Explorer (DAMPE) mission is one of the five scientific space science missions within the framework of the Strategic Pioneer Program on Space Science of the Chinese Academy of Science (CAS) approved in 2011. The main scientific objective of DAMPE is to detect electrons and photons in the range of 5GeV-10TeV with unprecedented energy resolution (1.5% at 100GeV) in order to identify possible Dark Matter (DM) signatures. It will also measure the flux of nuclei up to above 500TeV with excellent energy resolution (40% at 800GeV), which will bring new insights to the origin and propagation high energy cosmic rays. With its excellent photon detection capability, the DAMPE mission is well placed for new discoveries in high energy-ray astronomy as well.      

Study of >100 GeV electrons with BETS detector using a long duration balloon flight in Antarctica

We have observed cosmic-ray electrons from 10 to 1000 GeV by a long duration balloon flight using Polar Patrol Balloon (PPB) in Antarctica. The observation was carried out for 13 days at an altitude of 35 km in January 2004. The detector is an imaging calorimeter composed of scintillating-fiber belts and plastic scintillators inserted between lead plates. The geometrical factor of detector is about 600 cm²sr and the total thickness of lead absorber is 9 radiation lengths. The performance of the detector has been confirmed by the CERN-SPS beam test and also investigated by Monte-Carlo simulations. New telemetry system using a commercial satellite of iridium, power supply by solar batteries, and automatic level control using CPU have successfully been developed and operated during the flight. We have collected 5.7 × 10³ events over 100 GeV including nearly 100 candidates of primary electrons.