Gamma-ray burst investigation via polarimetry and spectroscopy (GRIPS)

The primary scientific goal of the GRIPS mission is to revolutionize our understanding of the early universe using γ-ray bursts. We propose a new generation gamma-ray observatory capable of unprecedented spectroscopy over a wide range of γ-ray energies (200 keV–50 MeV) and of polarimetry (200–1000 keV). The γ-ray sensitivity to nuclear absorption features enables the measurement of column densities as high as 10²⁸cm^− 2. Secondary goals achievable by this mission include direct measurements of all types of supernova interiors through γ-rays from radioactive decays, nuclear astrophysics with massive stars and novae, and studies of particle acceleration near compact stars, interstellar shocks, and clusters of galaxies. See for the authors’ affiliations.     

MAX, a Laue diffraction lens for nuclear astrophysics

The next generation of instrumentation for nuclear astrophysics will have to achieve a factor of 10–100 improvement in sensitivity over present technologies. With the focusing gamma-ray telescope MAX we take up this challenge: combining unprecedented sensitivity with high spectral and angular resolution, and the capability of measuring the polarization of the incident photons. The feasibility of such a crystal diffraction gamma-ray lens has recently been demonstrated with the prototype lens CLAIRE. MAX is a proposed mission which will make use of satellite formation flight to achieve 86 m focal length, with the Laue lens being carried by one satellite and the detector by the other. In the current design, the Laue diffraction lens of MAX will consist of 13740 copper and germanium (Ge_1−x Si _x , x ∼ 0.02) crystal tiles arranged on 36 concentric rings. It simultaneously focuses in two energy bands, each centred on one of the main scientific objectives of the mission: the 800–900 keV band is dedicated to the study of nuclear gamma-ray lines from type Ia supernovae (e.g. ⁵⁶ Co decay line at 847 keV) while the 450–530 keV band focuses on electron-positron annihilation (511 keV emission) from the Galactic centre region with the aim of resolving potential point sources. MAX promises a breakthrough in the study of point sources at gamma-ray energies by combining high narrow-line sensitivity (better than 10⁻⁶ cm⁻² s⁻¹) and high energy resolution (E/dE ∼ 500). The mission has successfully undergone a pre-phase A study with the French Space Agency CNES, and continues to evolve: new diffracting materials such as bent or composite crystals seem very promising. PACS: 95.55.Ka, 29.30.Kv, 61.10.-i     

High energy γ-radiation from the core of radio galaxy Centaurus A

The results of analysis of approximately 3 years of gamma-ray observations (August 2008-July 2011) of the radio galaxy Centaurus A with the Fermi Large Area Telescope (Fermi LAT) are presented. By modeling the surrounding (background) sources including the giant lobes of Centaurus A, and using the standard binned likelihood analysis method, the energy spectrum of the core is derived. In the energy range below several GeV it is described by a single power-law with photon index Γ = 2.73 ± 0.06 in agreement with the report of the Fermi LAT collaboration based on the first 10 months observations of the source. However, at higher energies the new data show significant excess above the extrapolation of the energy spectrum from low energies. The total flux between 200 MeV to 50 GeV is estimated to be (1.63 ± 0.14) × 10⁻⁷ ph cm⁻² s⁻¹. The comparison of the corresponding Spectral Energy Distribution (SED) at GeV energies with the SED in the TeV energy band reported by the H.E.S.S. collaboration shows that we deal with two or perhaps even three components of gamma-radiation originating from different regions located within the central 10 kpc of Centaurus A.     

DuneXpress

The DuneXpress observatory will characterize interstellar and interplanetary dust in-situ, in order to provide crucial information not achievable with remote sensing astronomical methods. Galactic interstellar dust constitutes the solid phase of matter from which stars and planetary systems form. Interplanetary dust, from comets and asteroids, represents remnant material from bodies at different stages of early solar system evolution. Thus, studies of interstellar and interplanetary dust with DuneXpress in Earth orbit will provide a comparison between the composition of the interstellar medium and primitive planetary objects. Hence DuneXpress will provide insights into the physical conditions during planetary system formation. This comparison of interstellar and interplanetary dust addresses directly themes of highest priority in astrophysics and solar system science, which are described in ESA’s Cosmic Vision. The discoveries of interstellar dust in the outer and inner solar system during the last decade suggest an innovative approach to the characterization of cosmic dust. DuneXpress establishes the next logical step beyond NASA’s Stardust mission, with four major advancements in cosmic dust research: (1) analysis of the elemental and isotopic composition of individual interstellar grains passing through the solar system, (2) determination of the size distribution of interstellar dust at 1 AU from 10^− 14 to 10^− 9 g, (3) characterization of the interstellar dust flow through the planetary system, (4) establish the interrelation of interplanetary dust with comets and asteroids. Additionally, in supporting the dust science objectives, DuneXpress will characterize dust charging in the solar wind and in the Earth’s magnetotail. The science payload consists of two dust telescopes of a total of 0.1 m² sensitive area, three dust cameras totaling 0.4 m² sensitive area, and a nano-dust detector. The dust telescopes measure high-resolution mass spectra of both positive and negative ions released upon impact of dust particles. The dust cameras employ different detection methods and are optimized for (1) large area impact detection and trajectory analysis of submicron sized and larger dust grains, (2) the determination of physical properties, such as flux, mass, speed, and electrical charge. A nano-dust detector searches for nanometer-sized dust particles in interplanetary space. A plasma monitor supports the dust charge measurements, thereby, providing additional information on the dust particles. About 1,000 grains are expected to be recorded by this payload every year, with 20% of these grains providing elemental composition. During the mission submicron to micron-sized interstellar grains are expected to be recorded in statistically significant numbers. DuneXpress will open a new window to dusty universe that will provide unprecedented information on cosmic dust and on the objects from which it is derived.     

The Solar Optical Telescope of Solar-B (Hinode): The Optical Telescope Assembly

The Solar Optical Telescope (SOT) aboard the Solar-B satellite (Hinode) is designed to perform high-precision photometric and polarimetric observations of the Sun in visible light spectra (388 – 668 nm) with a spatial resolution of 0.2 – 0.3 arcsec. The SOT consists of two optically separable components: the Optical Telescope Assembly (OTA), consisting of a 50-cm aperture Gregorian with a collimating lens unit and an active tip-tilt mirror, and an accompanying Focal Plane Package (FPP), housing two filtergraphs and a spectro-polarimeter. The optomechanical and optothermal performance of the OTA is crucial to attain unprecedented high-quality solar observations. We describe in detail the instrument design and expected stable diffraction-limited on-orbit performance of the OTA, the largest state-of-the-art solar telescope yet flown in space.     

Electron-positron annihilation lines and decaying sterile neutrinos

If massive sterile neutrinos exist, their decays into photons and/or electron-positron pairs may give rise to observable consequences. We consider the possibility that MeV sterile neutrino decays lead to the diffuse positron annihilation line in the Milky Way center, and we thus obtain bounds on the sterile neutrino decay rate Γ _e ≥10⁻²⁸ s⁻¹ from relevant astrophysical/cosmological data. Also, we expect a soft gamma flux of 1.2×10⁻⁴–9.7×10⁻⁴ ph cm⁻² s⁻¹ from the Milky Way center which shows up as a small MeV bump in the background photon spectrum. Furthermore, we estimate the flux of active neutrinos produced by sterile neutrino decays to be 0.02–0.1 cm⁻² s⁻¹ passing through the earth.     

Polarization Calibration of the Solar Optical Telescope onboard Hinode

The Solar Optical Telescope (SOT) onboard Hinode aims to obtain vector magnetic fields on the Sun through precise spectropolarimetry of solar spectral lines with a spatial resolution of 0.2 – 0.3 arcsec. A photometric accuracy of 10⁻³ is achieved and, after the polarization calibration, any artificial polarization from crosstalk among Stokes parameters is required to be suppressed below the level of the statistical noise over the SOT’s field of view. This goal was achieved by the highly optimized design of the SOT as a polarimeter, extensive analyses and testing of optical elements, and an end-to-end calibration test of the entire system. In this paper we review both the approach adopted to realize the high-precision polarimeter of the SOT and its final polarization characteristics.     

Energy-Dependent Timing of Thermal Emission in Solar Flares

We report solar flare plasma to be multi-thermal in nature based on the theoretical model and study of the energy-dependent timing of thermal emission in ten M-class flares. We employ high-resolution X-ray spectra observed by the Si detector of the “Solar X-ray Spectrometer” (SOXS). The SOXS onboard the Indian GSAT-2 spacecraft was launched by the GSLV-D2 rocket on 8 May 2003. Firstly we model the spectral evolution of the X-ray line and continuum emission flux F(ε) from the flare by integrating a series of isothermal plasma flux. We find that the multi-temperature integrated flux F(ε) is a power-law function of ε with a spectral index (γ)≈−4.65. Next, based on spectral-temporal evolution of the flares we find that the emission in the energy range E=4 – 15 keV is dominated by temperatures of T=12 – 50 MK, while the multi-thermal power-law DEM index (δ) varies in the range of −4.4 and −5.7. The temporal evolution of the X-ray flux F(ε,t) assuming a multi-temperature plasma governed by thermal conduction cooling reveals that the temperature-dependent cooling time varies between 296 and 4640 s and the electron density (n _e) varies in the range of n _e=(1.77 – 29.3)×10¹⁰ cm⁻³. Employing temporal evolution technique in the current study as an alternative method for separating thermal from nonthermal components in the energy spectra, we measure the break-energy point, ranging between 14 and 21±1.0 keV.     

Search for ultrahigh-energy cosmic gamma-ray bursts on the Baksan underground scintillation telescope

Based on data from the Baksan underground scintillation telescope (BUST) for the period 2001–2004, we searched for cosmic gamma-ray bursts (GRBs) at primary photon energies of 0.5 TeV or higher. We obtained constraints on the rate of bursts with durations of 1–10 s for fluences within the range 4.6 × 10⁻³-1.8 × 10⁻² erg cm⁻² in the declination band 30° ≤ δ ≤ 80°. We searched for ultrahigh-energy gamma rays from GRBs detected on spacecraft during and within ±2 h of the burst. No statistically significant excesses above the background of random coincidences were found. The derived constraints on the ultrahigh-energy gamma-ray fluence during GRBs lie within the range 4.6 × 10⁻³-3.7 × 10⁻² erg cm⁻².     

Allan Sandage and the cosmic expansion

This is an account of Allan Sandage’s work on (1) The character of the expansion field. For many years he has been the strongest defender of an expanding Universe. He later explained the CMB dipole by a local velocity of 220±50 km s⁻¹ toward the Virgo cluster and by a bulk motion of the Local supercluster (extending out to ∼3500 km s⁻¹) of 450–500 km s⁻¹ toward an apex at l=275, b=12. Allowing for these streaming velocities he found linear expansion to hold down to local scales (∼300 km s⁻¹). (2) The calibration of the Hubble constant. Probing different methods he finally adopted—from Cepheid-calibrated SNe Ia and from independent RR Lyr-calibrated TRGBs—H ₀=62.3±1.3±5.0 km s⁻¹ Mpc⁻¹.     

Characteristics of CMEs associated with solar flares and DH type II radio bursts based on source position

We studied the characteristics of Coronal Mass Ejections (CMEs) associated with solar flares and Deca-Hectometric (DH) type II radio bursts, based on source position during 23rd solar cycle (1997–2007). We classified these CME events into three groups using solar flare locations as, (i) disk events (0–30^∘); (ii) intermediate events (31–60^∘) and (iii) limb events (61–90^∘). Main results from this studies are, (i) the number of CMEs associated with solar flares and DH-type IIs decreases as the source position approaches from disk to limb, (ii) most of the DH CMEs are halo (72%) in disk events and the number of occurrence of halo CMEs decreases from disk to limb, (iii) the average width and speed of limb events (164^∘ and 1447 km s⁻¹) are higher than those of disk events (134^∘ and 1035 km s⁻¹) and intermediate events (146^∘ and 1170 km s⁻¹) and (iv) the average accelerations for disk, intermediate and limb events are −8.2 m s⁻², −10.3 m s⁻² and −4.5 m s⁻² respectively. These analysis of CMEs properties show more dependency on longitude and it gives strong evidence for projection effect.     

Acoustic Events in the Solar Atmosphere from <Emphasis Type="Italic">Hinode</Emphasis>/SOT NFI Observations

We investigate the properties of acoustic events (AEs), defined as spatially concentrated and short duration energy flux, in the quiet Sun, using observations of a 2D field of view (FOV) with high spatial and temporal resolution provided by the Solar Optical Telescope (SOT) onboard Hinode. Line profiles of Fe i 557.6 nm were recorded by the Narrow-band Filter Imager (NFI) on a 82″×82″ FOV during 75 min with a time step of 28.75 s and 0.08″ pixel size. Vertical velocities were computed at three atmospheric levels (80, 130, and 180 km) using the bisector technique, allowing the determination of energy flux to be made in the range 3 – 10 mHz using two complementary methods (Hilbert transform and Fourier power spectrum). Horizontal velocities were computed using local correlation tracking (LCT) of continuum intensities providing divergences. We found that the net energy flux is upward. In the range 3 – 10 mHz, a full FOV space and time averaged flux of 2700 W m⁻² (lower layer 80 – 130 km) and 2000 W m⁻² (upper layer 130 – 180 km) is concentrated in less than 1 % of the solar surface in the form of narrow (0.3″) AE. Their total duration (including rise and decay) is of the order of 10³ s. Inside each AE, the mean flux is 1.6×10⁵ W m⁻² (lower layer) and 1.2×10⁵ W m⁻² (upper). Each event carries an average energy (flux integrated over space and time) of 2.5×10¹⁹ J (lower layer) to 1.9×10¹⁹ J (upper). More than 10⁶ events could exist permanently on the Sun, with a birth and decay rate of 3500 s⁻¹. Most events occur in intergranular lanes, downward velocity regions, and areas of converging motions.     

EDGE: Explorer of diffuse emission and gamma-ray burst explosions

How structures of various scales formed and evolved from the early Universe up to present time is a fundamental question of astrophysical cosmology. EDGE (Piro et al., 2007) will trace the cosmic history of the baryons from the early generations of massive stars by Gamma-Ray Burst (GRB) explosions, through the period of galaxy cluster formation, down to the very low redshift Universe, when between a third and one half of the baryons are expected to reside in cosmic filaments undergoing gravitational collapse by dark matter (the so-called warm hot intragalactic medium). In addition EDGE, with its unprecedented capabilities, will provide key results in many important fields. These scientific goals are feasible with a medium class mission using existing technology combined with innovative instrumental and observational capabilities by: (a) observing with fast reaction Gamma-Ray Bursts with a high spectral resolution. This enables the study of their star-forming and host galaxy environments and the use of GRBs as back lights of large scale cosmological structures; (b) observing and surveying extended sources (galaxy clusters, WHIM) with high sensitivity using two wide field of view X-ray telescopes (one with a high angular resolution and the other with a high spectral resolution). The mission concept includes four main instruments: a Wide-field Spectrometer (0.1–2.2 eV) with excellent energy resolution (3 eV at 0.6 keV), a Wide-Field Imager (0.3–6 keV) with high angular resolution (HPD = 15”) constant over the full 1.4 degree field of view, and a Wide Field Monitor (8–200 keV) with a FOV of ? of the sky, which will trigger the fast repointing to the GRB. Extension of its energy response up to 1 MeV will be achieved with a GRB detector with no imaging capability. This mission is proposed to ESA as part of the Cosmic Vision call. We will outline the science drivers and describe in more detail the payload of this mission.     

Observations of Powerful Type III Bursts in the Frequency Range 10 – 30 MHz

The properties of powerful (flux >10⁻¹⁹ W m⁻² Hz⁻¹) type III bursts observed in July – August 2002 by the radio telescope UTR-2 at frequencies 10 – 30 MHz are analyzed. Most bursts have been registered when the active regions associated to these bursts were located near the central meridian or at 40° – 60° to the East or West from it. All powerful type III bursts drift from high to low frequencies with frequency drift rates 1 – 2.5 MHz s⁻¹. It is important to emphasize that according to our observations the drift rate is linearly increasing with frequency. The duration of the bursts changes mainly from 6 s at frequency 30 MHz up to 12 s at 10 MHz. The instantaneous frequency bandwidth does not depend on the day of observations, i.e. on the disk location of the source active region, and is increasing with frequency.     

ROSA: A High-cadence,Synchronized Multi-camera Solar Imaging System

The Rapid Oscillations in the Solar Atmosphere (ROSA) instrument is a synchronized, six-camera high-cadence solar imaging instrument developed by Queen’s University Belfast. The system is available on the Dunn Solar Telescope at the National Solar Observatory in Sunspot, New Mexico, USA, as a common-user instrument. Consisting of six 1k × 1k Peltier-cooled frame-transfer CCD cameras with very low noise (0.02 – 15 e s⁻¹ pixel⁻¹), each ROSA camera is capable of full-chip readout speeds in excess of 30 Hz, or 200 Hz when the CCD is windowed. Combining multiple cameras and fast readout rates, ROSA will accumulate approximately 12 TB of data per 8 hours observing. Following successful commissioning during August 2008, ROSA will allow for multi-wavelength studies of the solar atmosphere at a high temporal resolution.     

Stokes Diagnostics of 2D MHD-Simulated Solar Magnetogranulation

The properties of solar magnetic fields on scales less than the spatial resolution of solar telescopes are studied. A synthetic infrared spectropolarimetric diagnostic based on a 2D MHD simulation of magnetoconvection is used for this. Analyzed are two time sequences of snapshots that likely represent two regions of the network fields with their immediate surroundings on the solar surface with unsigned magnetic flux densities of 300 and 140 G. In the first region from the probability density functions of the magnetic field strength it is found that the most probable field strength at log τ ₅=0 is equal to 250 G. Weak fields (B<500 G) occupy about 70% of the surface, whereas stronger fields (B>1000 G) occupy only 9.7% of the surface. The magnetic flux is −28 G and its imbalance is −0.04. In the second region, these parameters are correspondingly equal to 150 G, 93.3%, 0.3%, −40 G, and −0.10. The distribution of line-of-sight velocities on the surface of log τ ₅=−1 is estimated. The mean velocity is equal to 0.4 km s⁻¹ in the first simulated region. The average velocity in the granules is −1.2 km s⁻¹ and in the intergranules it is 2.5 km s⁻¹. In the second region, the corresponding values of the mean velocities are equal to 0, −1.8, and 1.5 km s⁻¹. In addition the asymmetry of synthetic Stokes V profiles of the Fe i 1564.8 nm line is analyzed. The mean values of the amplitude and area asymmetry do not exceed 1%. The spatially smoothed amplitude asymmetry is increased to 10% whereas the area asymmetry is only slightly varied.     

The molecular hydrogen explorer H2EX

The Molecular Hydrogen Explorer, H2EX, was proposed in response to the ESA 2015 - 2025 Cosmic Vision Call as a medium class space mission with NASA and CSA participations. The mission, conceived to understand the formation of galaxies, stars and planets from molecular hydrogen, is designed to observe the first rotational lines of the H₂ molecule (28.2, 17.0, 12.3 and 9.7 μm) over a wide field, and at high spectral resolution. H2EX can provide an inventory of warm (≥ 100 K) molecular gas in a broad variety of objects, including nearby young star clusters, galactic molecular clouds, active galactic nuclei, local and distant galaxies. The rich array of molecular, atomic and ionic lines, as well as solid state features available in the 8 to 29 μm spectral range brings additional science dimensions to H2EX. We present the optical and mechanical design of the H2EX payload based on an innovative Imaging Fourier Transform Spectrometer fed by a 1.2 m telescope. The 20’×20’ field of view is imaged on two 1024×1024 Si:As detectors. The maximum resolution of 0.032 cm^− 1 (full width at half maximum) means a velocity resolution of 10 km s^− 1 for the 0 – 0 S(3) line at 9.7 μm. This instrument offers the large field of view necessary to survey extended emission in the Galaxy and local Universe galaxies as well as to perform unbiased extragalactic and circumstellar disks surveys. The high spectral resolution makes H2EX uniquely suited to study the dynamics of H₂ in all these environments. The mission plan is made of seven wide-field spectro-imaging legacy programs, from the cosmic web to galactic young star clusters, within a nominal two years mission. The payload has been designed to re-use the Planck platform and passive cooling design.

Cooling of magnetars with internal layer heating

We model thermal evolution of magnetars with a phenomenological heat source in a spherical internal layer and compare the results with observations of persistent thermal radiation from magnetars. We show that the heat source should be located in the outer magnetar’s crust, at densities ρ≲5×10¹¹ g cm⁻³, and the heating rate should be ∼10²⁰ erg cm⁻³ s⁻¹. Heating deeper layers is extremely inefficient because the thermal energy is mainly radiated away by neutrinos and does not warm up the surface to the magnetar’s level. This deep heating requires too much energy; it is inconsistent with the energy budget of neutron stars.      

InFOCμS Hard X-ray Imaging Telescope

InFOCμS is a new generation balloon-borne hard X-ray telescope with focusing optics and spectroscopy. We had a successful 22.5-hour flight from Fort Sumner, NM on September 16,17, 2004. In this paper, we present the performance of the hard X-ray telescope, which consists of a depth-graded platinum/carbon multilayer mirror and a CdZnTe detector. The telescope has an effective area of 49 cm² at 30 keV, an angular resolution of 2.4 arcmin (HPD), and a field of view of 11 arcmin (FWHM) depending on energies. The CdZnTe detector is configured with a 12 × 12 segmented array of detector pixels. The pixels are 2 mm square, and are placed on 2.1 mm centers. An averaged energy resolution is 4.4 keV at 60 keV and its standard deviation is 0.36 keV over 128 pixels. The detector is surrounded by a 3-cm thick CsI anti coincidence shield to reduce background from particles and photons not incident along the mirror focal direction. The inflight background is 2.9 × 10⁻⁴ cts cm⁻² sec⁻¹ keV⁻¹ in the 20–50 keV band.