Space-based Gamma-ray Telescopes Research Articles

The System of Anticoincidence Detectors of Space-Based Gamma-Ray Telescope GAMMA-400: The Characteristics Obtained Using Positron Beam of Synchrotron S-25R “PAKHRA” of the Lebedev Physical Institute, Russian Academy of Sciences

The System of Anticoincidence Detectors of Space-Based Gamma-Ray Telescope GAMMA-400: The Characteristics Obtained Using Positron Beam of Synchrotron S-25R “PAKHRA” of the Lebedev Physical Institute, Russian Academy of Sciences

Capabilities of the GAMMA-400 gamma-ray telescope to detect gamma-ray bursts from lateral directions

• The GAMMA-400 gamma-ray telescope performance for lateral aperture. • Detection of GRB from the lateral aperture in the energy range from ∼ 10 to ∼ 100 MeV. • The problem of connection between high- and low-energy gamma-ray emissions of GRBs. The currently developing space-based gamma-ray telescope GAMMA-400 will measure the gamma-ray and electron + positron fluxes using the main top-down aperture in the energy range from ∼ 20 MeV to several TeV in a highly elliptic orbit (without shading the telescope by the Earth and outside the radiation belts) continuously for a long time. The instrument will provide fundamentally new data on discrete gamma-ray sources, gamma-ray bursts (GRBs), sources and propagation of Galactic cosmic rays and signatures of dark matter due to its unique angular and energy resolutions in the wide energy range. The gamma-ray telescope consists of the anticoincidence system (AC), the converter-tracker (C), the time-of-flight system (S1 and S2), the position-sensitive and electromagnetic calorimeters (CC1 and CC2), scintillation detectors (S3 and S4) located above and behind the CC2 calorimeter and lateral detectors (LD) located around the CC2 calorimeter. In this paper, the capabilities of the GAMMA-400 gamma-ray telescope to measure fluxes of GRBs from lateral directions of CC2 are analyzed using Monte-Carlo simulations. The analysis is based on off-line second-level trigger construction using signals from S3, CC2, S4 and LD detectors. For checking the numerical algorithm the data from space-based GBM and LAT instruments of the Fermi experiment are used, namely, three long bursts: GRB 080916C, GRB 090902B, GRB 090926A and one short burst GRB 090510A. The obtained results allow us to conclude that from lateral directions the GAMMA-400 space-based gamma-ray telescope will reliably measure the spectra of bright GRBs in the energy range from ∼ 10 to ∼ 100 MeV with the on-axis effective area of about 0.13 m 2 for each of the four sides of CC2 and total field of view of about 6 sr.

Dark matter searches by the planned gamma-ray telescope GAMMA-400

Our paper reviews the planned space-based gamma-ray telescope GAMMA-400 and evaluates in details its opportunities in the field of dark matter (DM) indirect searches. We estimated the GAMMA-400 mean sensitivity to the diphoton DM annihilation cross section in the Galactic center for DM particle masses in the range of 1–500 GeV. We obtained the sensitivity gain at least by 1.2–1.5 times (depending on DM particle mass) with respect to the expected constraints from 12 years of observations by Fermi-LAT for the case of Einasto DM density profile. The joint analysis of the data from both telescopes may yield the gain up to 1.8–2.3 times. Thus the sensitivity reaches the level of annihilation cross section ⟨ σ v ⟩γγ(mχ = 100 GeV) ≈ 10−28 cm3/s. This will allow us to test the hypothesized narrow lines predicted by specific DM models, particularly the recently proposed pseudo-Goldstone boson DM model. We also considered the decaying DM—in this case the joint analysis may yield the sensitivity gain up to 1.1–2.0 times reaching the level of DM lifetime τγν(mχ = 100 GeV) ≈ 2 ⋅ 1029 s. We estimated the GAMMA-400 sensitivity to axion-like particle (ALP) parameters by a potential observation of the supernova explosion in the Local Group. This is very sensitive probe of ALPs reaching the level of ALP-photon coupling constant gaγ ∼ 10−13 GeV−1 for ALP masses ma ≲ 1 neV. We also calculated the sensitivity to ALPs by constraining the modulations in the spectra of the Galactic gamma-ray pulsars due to possible ALP-photon conversion. GAMMA-400 is expected to be more sensitive than the CAST helioscope for ALP masses ma ≈ (1−−10) neV reaching gaγmin ≈ 2 ⋅ 10−11 GeV−1. Other potentially interesting targets and candidates are briefly considered too.

The beam test of anticoincidence scintillation detector prototype with SiPM readout and perspectives of GRBs studies for space-based gamma-ray telescope GAMMA-400

The GAMMA-400 project will be the new generation of satellite gamma-observatory. GAMMA-400 space-based gamma-ray telescope represents the core of the scientific complex intended to perform a search for signatures of dark matter in the cosmic gamma-emission, measurements of diffuse gamma-emission characteristics, investigation of extended and point gamma-ray sources, studying of high energy component of gamma-ray bursts and solar flares emission. Four fast plastic sub-detectors of the gamma-ray telescope are included in fast trigger logic in the main telescope aperture. This aperture expected angular and energy resolution are ∼0.01° and ∼1-2% respectively for gammas with the energy >100 GeV and electron/protons rejection factor ∼5-105. Prototype of anticoincidence detector based on long BC-408 scintillators with SiPM readout for gamma-ray telescope was tested on a 300 MeV secondary positron beam of synchrotron C-25P «PAKHRA» of Lebedev Physical Institute in Russia. The measurement setup, design concepts for the prototype detector and chosen solutions together with some test results are discussed. Two other apertures (additional and lateral) allow analyzing transient events not required precision angular resolution, for examples, GRBs and solar flares. Similar plastics sub-detectors included in their fast trigger logic. Using of all three apertures allows making more effective observations of GRBs (better signal to noise ratio), more detailed study of its high energy afterglow due long term measurements (because of high apogee orbit provides low background variations with time) and detailed analysis of the sources luminosity variability (spectral, angular and temporal).

New method of high-energy gamma ray direction reconstruction in multilayered converters

A new method of high-energy gamma ray incident direction reconstruction is developed for gamma-ray detectors with multilayered converters. The method uses data from converter and, if available, from position-sensitive calorimeter to reconstruct an electromagnetic cascade axis and to determine the incident direction of a primary gamma. For the first time to find point of intersection of gamma direction line with convertor plane, median of energy deposit in sensitive plane of convertor is used. Applied, for example, to the GAMMA-400 space-based gamma-ray telescope this method allowed to achieve the angular resolution ∼0.01° at gamma-ray energy of 100 GeV, being much better than accuracy of the past and present space- and ground-based experiments. In the algorithm presented, a balance between the angular resolution and the effective area can be found to meet a scientific goal of an experiment.

Multiple Coulomb scattering method to reconstruct low-energy gamma–ray direction in the GAMMA-400 space-based gamma–ray telescope

The GAMMA-400 currently developing space-based gamma-ray telescope is designed to measure the gamma-ray fluxes in the energy range from ∼20 MeV to several TeV in the highly elliptic orbit (without shadowing the telescope by the Earth) continuously for a long time. The physical characteristics of the GAMMA-400 gamma-ray telescope, especially the angular and energy resolutions (at 100-GeV gamma rays they are ∼0.01° and ∼1%, respectively), allow us to consider this space-based experiment as the next step in the development of extraterrestrial high-energy gamma-ray astronomy. In this paper, a method to improve the reconstruction accuracy of incident angle for low-energy gamma rays in the GAMMA-400 space-based gamma-ray telescope is presented. The special analysis of topology of pair-conversion events in thin layers of converter was performed. Applying the energy dependence of multiple Coulomb scattering for pair components, it is possible to estimate the energies for each particle, and to use these energies as weight in the angle reconstruction procedure. To identify the unique track in each projection the imaginary curvature method is applied. It allows us to obtain significantly better angular resolution in comparison with other methods applied in current space-based experiments. When using this method for 50-MeV gamma rays the GAMMA-400 gamma-ray telescope angular resolution is about 4°.

High-energy gamma- and cosmic-ray observations with future space-based GAMMA-400 gamma-ray telescope

The future space-based GAMMA-400 gamma-ray telescope will be installed on the Navigator platform of the Russian Astrophysical Observatory. A highly elliptical orbit will provide observations for 7-10 years of many regions of the celestial sphere continuously for a long time (~ 100 days). GAMMA-400 will measure gamma-ray fluxes in the energy range from ~ 20 MeV to several TeV and electron + positron fluxes up to ~ 20 TeV. GAMMA-400 will have an excellent separation of gamma rays from the background of cosmic rays and electrons + positrons from protons and an unprecedented angular (~ 0.01° at Eγ = 100 GeV) and energy (~ 1% at Eγ = 100 GeV) resolutions better than for Fermi-LAT, as well as ground-based facilities, by a factor of 5-10. Observations of GAMMA-400 will provide new fundamental data on discrete sources and spectra of gamma-ray emission and electrons + positrons, as well as the nature of dark matter.

Robust constraints and novel gamma-ray signatures of dark matter that interacts strongly with nucleons

Due to shielding, direct detection experiments are in some cases insensitive to dark matter candidates with very large scattering cross sections with nucleons. In this paper, we revisit this class of models and derive a simple analytic criterion for conservative but robust direct detection limits. While large spin-independent cross sections seem to be ruled out, we identify potentially viable parameter space for dark matter with a spin-dependent cross section with nucleons in the range of ${10}^{\ensuremath{-}27}\text{ }\text{ }{\mathrm{cm}}^{2}\ensuremath{\lesssim}{\ensuremath{\sigma}}_{\mathrm{DM}\ensuremath{-}p}\ensuremath{\lesssim}{10}^{\ensuremath{-}24}\text{ }\text{ }{\mathrm{cm}}^{2}$. With these parameters, cosmic-ray scattering with dark matter in the extended halo of the Milky Way could generate a novel and distinctive gamma-ray signal at high galactic latitudes. Such a signal could be observable by Fermi or future space-based gamma-ray telescopes.

The Feasibility of Studying 44Ti(α, p)47V Reaction at Astrophysical Energies

The gamma-ray lines from the decay of 44Ti have been observed by space-based gamma-ray telescopes from two supernova remnants. It is believed that the 44Ti(α, p)47V reaction dominates the destruction of 44Ti. This work presents a possible technique to determine its reaction rate in forward kinematics at astrophysically relevant energies. Several online and offline measurements in parallel with Monte Carlo simulations were performed to illustrate the feasibility of performing this reaction. The results will be discussed.

Gamma-ray line measurements from supernova explosions

AbstractGamma ray lines are expected to be emitted as part of the afterglow of supernova explosions, because radioactive decay of freshly synthesised nuclei occurs. Significant radioactive gamma ray line emission is expected from56Ni and44Ti decay on time scales of the initial explosion (56Ni, τ ~days) and the young supernova remnant (44Ti,τ ~90 years). Less specific, and rather informative for the supernova population as a whole, are lessons from longer lived isotopes such as26Al and60Fe. From isotopes of elements heavier than iron group elements, any interesting gamma-ray line emission is too faint to be observable. Measurements with space-based gamma-ray telescopes have obtained interesting gamma ray line emissions from two core collapse events, Cas A and SN1987A, and one thermonuclear event, SN2014J. We discuss INTEGRAL data from all above isotopes, including all line and continuum signatures from these two objects, and the surveys for more supernovae, that have been performed by gamma ray spectrometry. Our objective here is to illustrate what can be learned from gamma-ray line emission properties about the explosions and their astrophysics.

Observing cosmic nuclei in gamma rays

Nucleosynthesis events in cosmic objects create new nuclei, admixtures of radioactive isotopes being part of the matter ejected into interstellar space by these events. Gamma rays are emitted in radioactive decays, and can be measured with space-based gamma-ray telescopes. Four mission years of INTEGRAL have led to discoveries of new sources and to detailed astronomical refinements of already-known gamma-ray line emission. As part of the main science objectives of INTEGRAL's spectrometer SPI, diffuse emission from annihilation of positrons has presented a new puzzle, as the Galactic distribution of their presumed sources does not agree with the gamma-ray image. Recent massive-star nucleosynthesis is traced throughout the Galaxy with radioactivites seen in 26Al and now also 60Fe gamma rays; precision line spectroscopy now reveals Doppler shifts for the 26Al line, separately for different parts of the Galaxy. This provides new insights into the dynamics of hot interstellar gas. The processes generating new atomic nuclei in stars and supernovae are reflected in the abundances of the ejected radioactivities. For individual supernovae, measurements of 44Ti with its 85 year decay time probes the symmetry of the supernova interior. Since such gamma-ray measurements probe the generation of new nuclei in cosmic sites through a radiation process which is independent of environmental parameters such as temperature or ionization, it will remain worthwhile to further develop instrumentation in this window to the nuclear-physics universe.

Gamma rays from cosmic radioactivities

Abstract— Gamma rays from radioactive byproducts of cosmic nucleosynthesis are direct messengers from nuclear processes taking place in various cosmic sites, and can be measured with telescopes operated in space. Due to low detector sensitivity, up until now, only a handful of sources have been detected in that electromagnetic window. Cobalt lines from SN1987A and 44Ti lines from the Cassiopeia A (Cas A) supernova remnant offer unique constraints on the properties of the innermost regions of core collapse supernovae. Diffuse gamma‐ray lines from the decay of radioactive 26Al and the annihilation of positrons are bright enough for mapping the Milky Way in the MeV regime, and are both measured by recent spaceborne spectrometers with unprecedented precision. This constrains the sources of Al production and the state of interstellar gas in the vicinity of these sites: the total mass of 26Al produced by stellar sources throughout the Galaxy is estimated to be ∼3 M⊙ per Myr, and the interstellar medium near those sources appears to be characterized by velocities of ∼100 km s−1. Positron annihilation must occur in a modestly ionized, warm phase of the interstellar medium, but at present the major positron production site(s) remain unknown. The spatial distribution of the annihilation gamma‐ray emission constrains positron production sites and positron propagation in the Galaxy. 60Fe radioactivity has been clearly detected recently; the flux ratio relative to 26Al of about 15% is on the lower side of predictions from massive star and supernova nucleosynthesis models. Those views at nuclear and astrophysical processes in and around cosmic sources by space‐based gamma‐ray telescopes offer invaluable information on cosmic nucleosynthesis.

An Overview of the Veritas Prototype Telescope and Camera

VERITAS (the Very Energetic Radiation Imaging Telescope Array System) is the next generation ground-based gamma-ray observatory that is being built in southern Arizona by a collaboration of ten institutions in Canada, Ireland, the U.K. and the U.S.A. VERITAS is designed to operate in the range from 50 GeV to 50 TeV with optimal sensitivity near 200 GeV; it will effectively overlap with the next generation of space-based gamma-ray telescopes. The first phase of VERITAS, consisting of four telescopes of 12 m aperture, will be operational by the time of the GLAST launch in 2007. Eventually the array will be expanded to include the full array of seven telescopes on a filled hexagonal grid of side 80 m. A prototype VERITAS telescope with a reduced number of mirrors and signal channels has been built. Its design and performance is described here. The prototype is scheduled to be upgraded to a full 499 pixel camera with 350 mirrors during the autumn of 2004.

Astrophysical constraints from gamma-ray spectroscopy

Gamma-ray lines from cosmic sources provide unique isotopic information, since they originate from energy level transitions in the atomic nucleus. Gamma-ray telescopes explored this astronomical window in the past three decades, detecting radioactive isotopes that have been ejected in interstellar space by cosmic nucleosynthesis events and nuclei that have been excited through collisions with energetic particles. Astronomical gamma-ray telescopes feature standard detectors of nuclear physics, but have to be surrounded by effective shields against local instrumental background, and need special detector and/or mask arrangements to collect imaging information. Due to exceptionally-low signal/noise ratios, progress in the field has been slow compared with other wavelengths. Despite the difficulties, this young field of astronomy is well established now, in particular due to advances made by the Compton Gamma-Ray Observatory in the 90ies. The most important achievements so far concern: short-lived radioactivities that have been detected in a couple of supernovae ( 56Co and 57Co in SN1987A, 44Ti in Cas A), the diffuse glow of long-lived 26Al that has been mapped along the entire plane of the Galaxy, several excited nuclei that have been detected in solar flares, and, last but not least, positron annihilation that has been observed in the inner Galaxy since the 70ies. High-resolution spectroscopy is now being performed: since 2002, ESAs INTEGRAL and NASAs RHESSI, two space-based gamma-ray telescopes with Ge detectors, are in operation. Recent results include: imaging and line shape measurements of e − – e + annihilation emission from the Galactic bulge, which can hardly be accounted for by conventional sources of positrons; 26Al emission and line width measurement from the inner Galaxy and from the Cygnus region, which can constrain the properties of the interstellar medium; and a diffuse 60Fe gamma-ray line emission which appears rather weak, in view of current theoretical predictions. Recent Galactic core-collapse supernovae are studied through 44Ti radioactivity, but, apart from Cas A, no other source has been found; this is a rather surprising result, assuming a canonical Galactic supernova rate of ∼ 1 / 50 years. The characteristic signature of 22Na-line emission from a nearby O Ne Mg novae is expected to be measured during INTEGRALs lifetime.

The calibration and environmental testing of the engineering module of GLAST CsI calorimeter

GLAST is the next generation space-based gamma ray telescope for the energy range 30 MeV-300 GeV, to be launched by NASA in 2007. For photon energy measurements it will use a CsI crystal calorimeter made of 16 identical modules. The engineering module (EM) calorimeter is the first full scale prototype built with the same technology as flight modules to verify the design and technological choices before starting calorimeter production. The module contains 96 CsI crystals, supported by a carbon fiber composite structure and read out with silicon PIN photodiodes from both ends. In this paper, we report the results of EM calibration using cosmic ray muons and charge injection during environmental tests. The EM showed stable functioning in the required temperature range from -30 C to +50 C during six months of continuous testing, including seven thermal vacuum cycles between -30 C and +50 C and vibration testing with amplitudes significantly higher than expected during launch. None of 96 crystals experienced mechanical or optical degradation after the tests. The longitudinal position measurement is accomplished using light asymmetry from two ends of each crystal, providing /spl sim/6--12 mm position resolution (2-4% of crystal length) for cosmic ray muons. The production of flight modules will start in late 2003.

Gamma Large Area Silicon Telescope (GLAST) applying silicon strip detector technology to the detection of gamma rays in space

The recent discoveries and excitement generated by space satillite experiment EGRET (presently operating on the Compton Gamma Ray Observatory (CGRO)) have prompted an investigation into modern detector technologies for the next generation of space based gamma ray telescopes. The GLAST proposal is based on silicon strip detectors as the “technology of choice” for space application: no consumables, no gas volume, robust (versus fragile), long lived, and self-triggerable. The GLAST detector basically has two components: a tracking module preceding a calorimeter. The tracking module has planes of crossed strip ( x, y) 300 μm pitch silicon detectors coupled to a thin radiator to measure the coordinates of converted electron-positron pairs. The gap between the layers (∼ 5 cm) provides a lever arm for track fitting resulting in an angular resolution of < 0.1° at high energy. The status of this R & D effort is discussed including details on triggering the instrument, the organization of the detector electronics and readout, and work on computer simulations to model this instrument.