Constraining dark matter properties with SPI

Using the high-resolution spectrometer SPI on board the International Gamma-Ray Astrophysics Laboratory ( INTEGRAL ), we search for a spectral line produced by a dark matter (DM) particle with a mass in the range  40 keV < M _DM < 14 MeV  , decaying in the DM halo of the Milky Way. To distinguish the DM decay line from numerous instrumental lines found in the SPI background spectrum, we study the dependence of the intensity of the line signal on the offset of the SPI pointing from the direction toward the Galactic Centre. After a critical analysis of the uncertainties of the DM density profile in the inner Galaxy, we find that the intensity of the DM decay line should decrease by at least a factor of 3 when the offset from the Galactic Centre increases from 0° to 180°. We find that such a pronounced variation of the line flux across the sky is not observed for any line, detected with a significance higher than 3σ in the SPI background spectrum. Possible DM decay origin is not ruled out only for the unidentified spectral lines, having low (∼3σ) significance or coinciding in position with the instrumental ones. In the energy interval from 20 keV to 7 MeV, we derive restrictions on the DM decay line flux, implied by the (non-)detection of the DM decay line. For a particular DM candidate, the sterile neutrino of mass M _DM, we derive a bound on the mixing angle.     

Galactic 1.275-MeV emission from ONe novae and its detectability by INTEGRAL/SPI

Models of Galactic 1.275‐MeV emission produced by the decay of the radionuclide ²²Na have been computed. Several frequency–spatial distributions of novae have been investigated using recent results of nova rates and spatial distributions of novae in our Galaxy. These models allow us to estimate the lower limit of the ²²Na mass ejected per ONe nova detectable with the future spectrometer (SPI) of the INTEGRAL observatory as a function of the frequency–spatial distribution of ONe novae in the Galaxy. Calculations using recent estimations of the expected ²²Na mass ejected per ONe nova show that the detection of the Galactic emission of 1.275‐MeV photons will be difficult with the future spectrometer of the INTEGRAL observatory, whereas the cumulative emission around the Galactic Centre has some chance of being detected during the deep survey of the central radian of the Galaxy.     

Instrumental lines of astrophysical relevance in TGRS and SPI

High resolution γ-ray spectroscopy at energies around 1 MeV, as with SPI on board INTEGRAL, is a powerful tool for astronomy with radioactivities. We do not expect the SPI signal-to-background ratio for any of the anticipated γ-ray sources to exceed a few percent; hence detailed modelling of the instrumental background will be crucial. We exploit the similarities between TGRS on board WIND and SPI with respect to orbit and radiation environment, as well as detector design and material composition, to anticipate the most important instrumental background lines and their production channels in SPI at the energies of selected γ-ray lines of astrophysical relevance.     

Pre-launch calibration campaign of the gamma-ray spectrometer aboard the INTEGRAL satellite

The SPI, Spectrometer aboard the ESA INTEGRAL satellite, to be launched in 2002, will study the gamma ray sky in the 20 keV to 8 MeV energy band with a spectral resolution of 2 keV for photons of 1 MeV thanks to its 19 germanium detectors. A coded mask imaging technique provides for a 2° angular resolution. An active BGO veto shield is used for background rejection. After the integration and test campaigns at CNES in Toulouse, the flight model of SPI has recently undergone a 1 month pre-launch calibration campaign at the CEA center of Bruyères le Châtel, using an accelerator for homogeneity measurements and high activity radioactive sources for imaging performance measurements. We report on the operational aspects of those measurements, whose analysis is foreseen to be published before launch.     

Multiple acceleration of protons on the Sun and their free propagation to the Earth on January 20, 2005

We analyze the observations of solar protons with energies >80 MeV near the Earth and the January 20, 2005, solar flare in various ranges of the electromagnetic spectrum. Within approximately the first 30 min after their escape into interplanetary space, the solar protons with energies above 80 MeV propagated without scattering to the Earth and their time profiles were determined only by the time profile of the source on the Sun and its energy spectrum. The 80–165 MeV proton injection function was nonzero beginning at 06:43:80 UT and can be represented as the product of the temporal part, the ACS (Anticoincidence System) SPI (Spectrometer on INTEGRAL) count rate, and the energy part, a power-law proton spectrum ～E ^?4.7±0.1. Protons with energies above 165 MeV and relativistic electrons were injected, respectively, 4 and 9 min later than this time. The close correlation between high-energy solar electromagnetic emission and solar proton fluxes near the Earth is evidence for prolonged and multiple proton acceleration in solar flares. The formation of a posteruptive loop system was most likely accompanied by successive energy releases and acceleration of charged particles with various energies. Our results are in conflict with the ideas of cosmic-ray acceleration in gradual solar particle events at the shock wave driven by a coronal mass ejection.     

Cosmic-ray streaming and anisotropies

The principal result of this paper is the demonstration that in interplanetary space the electric-field drifts and convective flow parallel to the magnetic field of cosmic-ray particles combine as a simple convective flow with the solar wind. In addition there are diffusive currents and transverse gradient drift currents. With this interpretation direct reference to the interplanetary electric-field drifts is eliminated and the study of steady-state and transient cosmic-ray anisotropies is both more systematic and simpler. Following a discussion of our present knowledge of the diffusion coefficient in the interplanetary medium, the theory is applied to steady-state anisotropies near Earth in the kinetic energy (T) range 7.5 MeV<T<20 GeV. First the theory of the diurnal variation atT>-2 GeV is examined and it is suggested that the azimuthal streaming associated with the observations be regarded simply as proof that there is no significant net radial flow of cosmic rays at these energies. Second, it is predicted that, near Earth, the radial anisotropy will have a (+?+) variation with energy and this prediction is very insensitive to the precise values of the parameters used: intensity spectrum, solar wind speed, radial density gradient, and diffusion coefficient. Then, third, the small and radial steady-state anisotropies reported by Raoet al. (1967) in the intervals 7.5<T<45 MeV and 45<T<90 MeV are re-examined and it is found that the gradients and diffusion coefficients required to produce the reported anisotropies in 7.5<T<45 MeV are inconsistent with those expected from other data.     

On the theory of annihilation lines in gamma-ray bursts

The mechanism of formation of an annihilation line 0.5 MeV in gamma-ray bursts due to electron-positron pair production in strong magnetic fields of neutron stars is discussed. Bremsstrahlung from a hot polar spot is supposed to be a source of gamma-quanta which produce the pairs. It is shown that a great part of radiation with the energyE>2mc ² per quantum (except for directions along or close to the magnetic field) is consumed by pair production and does not excape from the gamma-burster. This indicates a possible strong gap in continuum radiation at energies higher than 1 MeV. At the same time effective creation of pairs enables one to give a simple estimate of the expected annihilation line intensity in gamma-ray burst spectra. This estimate coincides with the available observational data.     

Spectrum of the relic neutrino background from past supernovae and cosmological models

It is greatly expected that the relic neutrino background from past supernovae will be detected by Superkamiokande (SK) which is now under construction. We calculate the spectrum and the event rate at SK systematically by using the results of simulations of a supernova explosion and reasonable supernova rates. We also investigate the effect of a cosmological constant, Λ, on the spectrum, since some recent cosmological observations strongly suggest the existence of Λ. We find following results. (1) The spectrum has a peak at about 3 MeV, which is much lower than that of previous estimates (6–10 MeV). (2) The event rate at SK in the range from 10 MeV to 50 MeV, where the relic neutrinos from past supernovae are dominant, is about 25h₅₀²(R_SN/0.1 yr⁻¹)(n_Gh₅₀⁻³/0.02 Mpc⁻³) events per year, where R_SN is the supernova rate in a galaxy, n_G is the number density of galaxies, and h₅₀ = H₀/(50 km/s Mpc), where H₀ is the Hubble constant. (3) The event rate is almost insensitive to Λ. The flux increases in the low energy side (< 10 MeV) with increasing Λ, but decreases in the high energy side (> 10 MeV) in models in which the integrated number of supernovae in one galaxy is fixed.     

Exploring the Capabilities of the Anti-Coincidence Shield of the International Gamma-Ray Astrophysics Laboratory (INTEGRAL) Spectrometer to Study Solar Flares

The International Gamma-Ray Astrophysics Laboratory (INTEGRAL) is a European Space Agency hard X-ray/γ-ray observatory for astrophysics, covering photon energies from 15 keV to 10 MeV. It was launched in 2002, and since then the Bismuth Germanate (BGO) detectors of the Anti-Coincidence Shield (ACS) of the Spectrometer on INTEGRAL (SPI) have detected many hard X-ray (HXR) bursts from the Sun, producing light curves at photon energies above ≈?100 keV. The spacecraft has a highly elliptical orbit, providing long uninterrupted observing (about 90 % of the orbital period) with nearly constant background due to the shorter time needed to cross Earth’s radiation belts. However, because of technical constraints, INTEGRAL cannot be pointed at the Sun, and high-energy solar photons are always detected in nonstandard observation conditions. To make the data useable for solar studies, we have undertaken a major effort to specify the observing conditions through Monte Carlo simulations of the response of ACS for several selected flares. We checked the performance of the model employed for the Monte Carlo simulations using the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) observations for the same sample of solar flares. We conclude that although INTEGRAL was not designed to perform solar observations, ACS is a useful instrument for solar-flare research. In particular, its relatively large effective area allows determining good-quality HXR/γ-ray light curves for X- and M-class solar flares and, in some cases, probably also for C-class flares.     

Stereoscopic observations of solar flares made onboard the 2001 Mars Odyssey spacecraft and CORONAS-F satellite

The results of observations of solar hard radiation recorded by two spacecraft—2001 Mars Odyssey and CORONAS-F—which were located in the vicinity of Mars and Earth, respectively, are discussed. The HEND instrument, developed at the Space Research Institute of the Russian Academy of Sciences, recorded photons with energies ranging from 80 keV to 2 MeV, and the SPR and SONG instruments, developed at the Skobeltsyn Research Institute of Nuclear Physics of the Moscow State University, detected radiation in the energy interval from 15 keV to 100 MeV. The rising of the sunspot group 10486 in late October 2003, which had been observed from Martian orbit before it was seen from the Earth’s surface, is analyzed in detail. In this case, observations made from directions that differ by 24° showed a close-to-24 h advance for the detection of hard radiation of flares. Stereoscopic observations of M-class flares near the limb show that the overwhelming part of radiation with energies above 80 keV arises at heights that do not exceed 7–10 thousand km. Also reported are the results of observations of the powerful flare on August 25, 2001, by the two devices, which complement each other substantially. The processes resulting in the formation of high-energy radiation of solar flares are discussed.     

The Evolution of the Interstellar Medium over Cosmic Time

C23 UV spectroscopy of the PG1159-type star NGC7094 C26 Variations of the radio synchrotron spectral index in the interstellar medium of M33 C38 Angular Momentum Evolution of Young Brown Dwarfs and Low Mass Stars C48 The radio halo of the nearby starburst galaxy NGC 253 C95 Signatures of early metal enrichment in Damped-Lyman Alpha systems C113 CO 4 → 3 and [CI] 1 → 0 in the centers of NGC4945 and Circinus C115 Ratio of atomic and molecular gas and gravitational stabilty in the disk of M51 C130 The Interstellar Mediumat Early Cosmic Times: Molecular Gas in Distant Quasar Host Galaxies C188 Probing the interstellar medium in distant galaxies with SPICA/ESI C191 The evolution of spectral energy distributions of galaxies over cosmic times C197 Observations of 60Fe in the Galaxy with INTEGRAL/SPI C204 Evolution of Interstellar Clouds in a hot Gas Environment C205 The effect of clouds in a galactic wind on the evolution of gas-rich dwarf galaxies C206 Energy and element deposit into the interstellar medium during the lives of massive stars C209 The distribution and kinematics of massive stars in the inner Galaxy mapped with SPI/INTEGRAL 26Al 1.8 MeV line observations C213 PDR modelling of the Galactic FIR line emission C239 Towards a complete picture of the molecular ISM in local Luminous Infrared Galaxies: first results from the JCMT/IRAM line survey C242 The Search for the Very High-redshift Tail of Submillimeter Galaxies     

The solar modulation of electrons in the heliosphere

The propagation and modulation of electrons in the heliosphere play an important part in improving our understanding and assessment of the modulation processes. A full three-dimensional numerical model is used to study the modulation of galactic electrons, from Earth into the inner heliosheath, over an energy range from 10 MeV to 30 GeV. The modeling is compared with observations of 6–14 MeV electrons from Voyager 1 and observations at Earth from the PAMELA mission. Computed spectra are shown at different spatial positions. Based on comparison with Voyager 1 observations, a new local interstellar electron spectrum is calculated. We find that it consists of two power-laws: In terms of kinetic energy E, the results give E ^?1.5 below ～500 MeV and E ^?3.15 at higher energies. Radial intensity profiles are computed also for 12 MeV electrons, including a Jovian source, and compared to the 6–14 MeV observations from Voyager 1. Since the Jovian and galactic electrons can be separated in the model, we calculate the intensity of galactic electrons below 100 MeV at Earth. The highest possible differential flux of galactic electrons at Earth with E=12 MeV is found to have a value of 2.5×10^?1 electrons m^?2?s^?1?sr^?1?MeV^?1 which is significantly lower (a factor of 3) than the Jovian electron flux at Earth. The model can also reproduce the extraordinary increase of electrons by a factor of 60 at 12 MeV in the inner heliosheath. A lower limit for the local interstellar spectrum at 12 MeV is estimated to have a value of (90±10) electrons m^?2?s^?1?sr^?1?MeV^?1.     

The gamma ray spectrometer for the Solar Maximum Mission

The Solar Maximum Mission Gamma Ray Experiment (SMM GRE) utilizes an actively shielded, multicrystal scintillation spectrometer to measure the flux of solar gamma rays. The instrument provides a 476-channel pulse height spectrum (with energy resolution of 7% at 662 keV) every 16.38 s over the energy range 0.3–9 MeV. Higher time resolution (2 s) is available in three windows between 3.5 and 6.5 MeV to study prompt gamma ray line emission at 4.4 and 6.1 MeV. Gamma ray spectral analysis can be extended to 15 MeV on command. Photons in the energy band from 300–350 keV are recorded with a time resolution of 64 ms. A high energy configuration also gives the spectrum of photons in the energy range from 10–100 MeV and the flux of neutrons 20 MeV. Both have a time resolution of 2 s. Auxiliary X-ray detectors will provide spectra with 1-sec time resolution over the energy range of 10–140 keV. The instrument is designed to measure the intensity, energy, and Doppler shift of narrow gamma ray lines as well as the intensity of extremely broadened lines and the photon continuum. The main objective is to use this time and spectral information from both nuclear gamma ray lines and the photon continuum in a direct study of the dynamics of the solar flare/particle acceleration phenomena.     

Gamma-ray lines observed in balloon flights at high rigidity

Gamma-ray lines at 0.511 MeV and 1.632 MeV have been observed at high rigidity (12.5 GV), and up to 4 g cm^–2, during stratospheric balloon flights launched from São José dos Campos, Brazil. The flux of these lines are compared with the results obtained at other rigidity regions. The intensity variations of the most prominent of these lines, the annihilation line at 0.511 MeV, is found to be compatible, at various atmospheric depths, with theoretical predictions. This study has led to the estimation of an upper limit for the flux of the extra-terrestrial 0.511 MeV gamma-ray line.     

Could a plasma in quasi-thermal equilibrium be associated to the “orphan” TeV flares?

TeV γ-ray detections in flaring states without activity in X-rays from blazars have attracted much attention due to the irregularity of these “orphan” flares. Although the synchrotron self-Compton model has been very successful in explaining the spectral energy distribution and spectral variability of these sources, it has not been able to describe these atypical flaring events. On the other hand, an electron–positron pair plasma at the base of the AGN jet was proposed as the mechanism of bulk acceleration of relativistic outflows. This plasma in quasi-thermal equilibrium called Wein fireball emits radiation at MeV-peak energies serving as target of accelerated protons. In this work we describe the “orphan” TeV flares presented in blazars 1ES 1959+650 and Mrk 421 assuming geometrical considerations in the jet and evoking the interactions of Fermi-accelerated protons and MeV-peak target photons coming from the Wein fireball. After describing successfully these “orphan” TeV flares, we correlate the TeV γ-ray, neutrino and UHECR fluxes through pγ interactions and calculate the number of high-energy neutrinos and UHECRs expected in IceCube/AMANDA and TA experiment, respectively. In addition, thermal MeV neutrinos produced mainly through electron–positron annihilation at the Wein fireball will be able to propagate through it. By considering two- (solar, atmospheric and accelerator parameters) and three-neutrino mixing, we study the resonant oscillations and estimate the neutrino flavor ratios as well as the number of thermal neutrinos expected on Earth.     

Convective transport of low energy cosmic rays in the interplanetary region

A complete solution has been obtained of the steady-state transport equations, including energy losses, for cosmic-rays in the interplanetary region for conditions in which diffusive transport is negligible and convective effects dominate. The region of validity of the solution will in general be a shell between heliocentric radiiR ₁ andR ₂ (R ₂ may be infinite). The precise range of kinetic energyT and heliocentric radiusr in which the solution is valid is not known but it appears to be applicable in the vicinity of Earth to protons withT≤1 MeV. ForT～0.5 MeV near Earth,R ₁ may be ～0.5 AU andR ₁ will decrease asT, observed near Earth, decreases. The solution is simple in form but quite general; it predicts the differential number densityU (r, T) in terms of that observed at radius a (near Earth, say). Thus it may be quite useful in interpreting and co-ordinating steady-state cosmicray observations atT～1 MeV. The differential and integral intensities, differential anisotropy and differential radial-gradient at (r, T) also are determined. A simple interpretation of the solution is given in terms of energy losses due to adiabatic deceleration of the particles as they are being convected outward from the Sun. This leads to the useful notion of following a particle in (r, T) as it increasesr and decreasesT. Particles convected from the outer corona to Earth decrease their kinetic energy by factor ～500.Following a particle the Compton-Getting factor remains constant. Particles observed at (a, T) in convective transport have come from nearer the Sun; they may be of solar origin but may also be of galactic origin having penetrated tor<R ₁   

Nuclear line spectroscopy of solar flares

The study of nuclear line spectra from solar flares holds a rich promise for elucidating the properties of both the accelerated particles and the interaction or target region. We review the observations and the analysis of the large nuclear line rich flare which occurred near the west limb starting at 08:03 UT on 27 April, 1981. The observed spectrum from this flare contains three intense and isolated gamma-ray lines which can be analyzed in a model independent way. The measured energies are 1.628 ± 0.008, 4.430 ± 0.011, and 6.147 ± 0.022 MeV, identifying them as the de-excitation lines of ²⁰Ne (1.634 MeV), ¹²C (4.438 MeV), and ¹⁶O (6.129 MeV). Elemental abundances of the ambient gas at the site of gamma-ray line production in the solar atmosphere are deduced using these gamma-ray line observations. The resultant abundances are different from local galactic abundances which are thought to be similar to photospheric abundances.Resident Research Associate at NRL under the NRC Associateship Program.     

Simultaneous observations of relativistic electron bursts and neutral-line signatures in the magnetotail

The relationship between the relativistic electron bursts (0.3 ～ 1.0 MeV) observed in the magnetotail at X = ?20 ～ ?30 R_e and the evolution of the structure of the magnetotail during substorms is investigated. It is found that the majority of the relativistic electron bursts are associated with the substorm activity and occurs inside the plasma sheet at the time of the local BZ-southward turning. It is suggested that these electrons are accelerated at the neutral line and trapped in the magnetic loop structure.