Solar X-ray Monitor (XSM) on-board Chandrayaan-2 orbiter

The remote X-ray fluorescence spectroscopy is a powerful technique to investigate the elemental abundances in the atmosphere-less planetary bodies. The experiment involves measuring spectra of fluorescent X-rays from lunar surface using a low energy X-ray detector onboard an orbiting satellite. Since the flux of fluorescent X-ray lines critically depend on the flux and spectrum of the incident solar X-rays, it is essential to have simultaneous and accurate measurement of X-ray from both Moon and Sun. In the context of Moon, this technique has been employed since early days of space exploration to determine elemental composition of lunar surface. However, so far it has not been possible to exploit it to its full potential due to various reasons. Therefore it is planned to continue the remote X-ray fluorescence spectroscopy experiment on-board Chandrayaan-2 which includes both lunar X-ray observations and solar X-ray observations as two separate payloads. The lunar X-ray observations will be carried out by Chandra Large Area Soft x-ray Spectrometer (CLASS) experiment; whereas the solar X-ray observations will be carried out by a separate payload, Solar X-ray Monitor (XSM). Here we present the overall design of the XSM instrument, the present development status as well as preliminary results of the laboratory model testing. XSM instrument will have two packages namely – XSM sensor package and XSM electronics package. XSM will accurately measure spectrum of Solar X-rays in the energy range of 1–15 keV with energy resolution ∼200 eV @ 5.9 keV. This will be achieved by using state-of-the-art Silicon Drift Detector (SDD), which has a unique capability of maintaining high energy resolution at very high incident count rate expected from Solar X-rays. XSM onboard Chandrayaan-2 will be the first experiment to use such detector for Solar X-ray monitoring.     

Current status of X-ray spectrometer development in the SELENE project

The X-ray spectrometer (XRS) on the SELENE (SELenological and ENgineering Explorer) spacecraft, XRS, will observe fluorescent X-rays from the lunar surface. The energy of the fluorescent X-ray depends on the elements of which the lunar soil consists, therefore we can determine elemental composition of the upper most lunar surface. The XRS consists of three components: XRF-A, SOL-B, and SOL-C. XRF-A is the main sensor to observe X-rays from the lunar surface. SOL-B is direct monitor of Solar X-ray using Si-PIN photodiode. SOL-C is another Solar X-ray monitor but observes the X-rays from the standard sample attached on the base plate. This enables us to analyze by a comparative method similar to typical laboratory XRF methods. XRF-A and SOL-C adopt charge coupled device as an X-ray detector which depletion layer is deep enough to detect X-rays. The X-ray spectra were obtained by the flight model of XRS components, and all components has been worked well to analyze fluorescent X-rays. Currently, development of the hardware and software of the XRS has been finished and we are preparing for system integration test for the launch.     

Astrophysical motivation for X-ray polarimetry

In this paper I will review the motivation for measuring polarization in the X-ray band from astrophysical sources. Emission models designed to reproduce X-ray spectra can be tested using polarization, and polarization detected in other wavelength bands makes clear predictions as to the X-ray polarization. Polarization is a powerful tool to infer geometrical properties of sources which are too small to be spatially resolved. At the same time, there has been recent progress in instrumentation which is likely to allow searches for X-ray polarization at levels significantly below what was possible for early detectors. This paper will review the history of X-ray polarimetry, discuss some experimental techniques and the scientific problems which can be addressed by future experiments.     

A hybrid X-ray imaging spectrometer for NeXT and the next generation X-ray satellite

We propose a new type of wide band X-ray imaging spectrometer as a focal plane detector of the super mirror onboard on future X-ray missions including post Astro-E2. This camera is realized by the hybrid of back illumination CCDs and a back supportless CCD for 0.05–10 keV band, and a Micro Pixel Gas Chamber detecting X-rays at 10–80 keV.     

Mapping lunar surface chemistry: New prospects with the Chandrayaan-2 Large Area Soft X-ray Spectrometer (CLASS)

Surface chemistry of airless bodies in the solar system can be derived from remote X-ray spectral measurements from an orbiting spacecraft. X-rays from planetary surfaces are excited primarily by solar X-rays. Several experiments in the past have used this technique of X-ray fluorescence for deriving abundances of the major rock forming elements. The Chandrayaan-2 orbiter carries an X-ray fluorescence experiment named CLASS that is designed based on results from its predecessor C1XS flown on Chandrayaan-1. We discuss the new aspects of lunar science that can be potentially achieved with CLASS.     

Flare buildup in X-rays,UV, microwaves and white light

Coordinated observations using space and ground-based instruments were made of active region complex #2522/2530, 24–30 June, 1980. The 10 largest flares from these regions were of importance M1-M6 in X-rays, and all were observed from satellites, except for one observed from a balloon. Several kinds of buildup signature have been found in the tens of minutes before these flares. Among these signatures are the following: 1) Relative faintness in X-ray lines of the pre-flare pixels, 2) X-ray (5–15 keV) “flashes” at points displaced by 1′–2′ from the flare site, 3) Rising filaments seen in Hα and Ultraviolet 4) Microwave intensification, polarization increase and polarization flip 5) Coronal disturbances above limb flares at or before the impulsive phase.     

Supersoft X-ray sources

More than 100 supersoft X-ray sources (SSS) are reported in 20 external galaxies, the Magellanic Clouds (MCs) and our Galaxy. The effective temperatures of the brighter SSS are 20–100 eV. SSS with luminosities below ≈3 × 10³⁸ erg s⁻¹ are consistent with accreting white dwarfs (WDs) with steady nuclear burning or post-novae. Optical identifications exist for SSS in our Galaxy and the MCs (including orbital period determinations) and for SSS in M31 (with novae and symbiotic stars, SySs). High resolution X-ray spectra of the brightest SSS in our Galaxy and the MCs reveal the existence of spectral features due to high gravity WDs. Timing studies in X-rays (combined with the optical) of the stable nuclear burning phase in steady nuclear burning sources and in post-novae allow to constrain the mass accretion rate onto and the mass of the nuclear burning WD. The nature of a few SSS with luminosities 10³⁹ erg s⁻¹ remains unclear.     

Solar system planets observed with Suzaku

Recent results of solar system planets observed with the Japanese X-ray astronomy satellite Suzaku are reviewed. Thanks to the low instrumental background and good energy resolution, X-ray CCDs onboard Suzaku are one of the best probes to study diffuse X-ray emission. An overview of the Suzaku data of Jupiter and Earth is presented, along with preliminary results of Mars. Firstly, diffuse hard X-ray emission is discovered in 1–5 keV at Jovian radiation belts. Its spectrum is represented by a power-law continuum with a photon index of ∼1.4. This emission could originate from inverse-Compton scattering of solar photons by tens MeV electrons. Secondly, variable diffuse soft X-rays are serendipitously found during observations in the directions of the north ecliptic pole and galactic ridge. Good time correlations with the solar wind and emission lines found in the X-ray spectra are firm evidences of a solar wind charge exchange emission with Earth’s exosphere. Thirdly, diffuse X-ray emission from Martian exosphere via the solar wind charge exchange is investigated for the first time at solar minimum. A stringent upper limit on the density of the Martian exosphere is placed from the Suzaku data.     

The gas pixel detector as a solar X-ray polarimeter and imager

The Sun is the nearest astrophysical source with a very intense emission in the X-ray band. The study of energetic events, such as solar flares, can help us to understand the behaviour of the magnetic field of our star. There are in the literature numerous studies published about polarization predictions, for a wide range of solar flares models involving the emission from thermal and/or non-thermal processes, but observations in the X-ray band have never been exhaustive.The gas pixel detector (GPD) was designed to achieve X-ray polarimetric measurements as well as X-ray images for far astrophysical sources. Here we present the possibility to employ this instrument for the observation of our Sun in the X-ray band.     

Modeling the broadband persistent emission of magnetars

In this paper, we discuss our first attempts to model the broadband persistent emission of magnetars within a self-consistent, physical scenario. We present the predictions of a synthetic model that we calculated with a new Monte Carlo 3D radiative code. The basic idea is that soft thermal photons (e.g. emitted by the star surface) can experience resonant cyclotron upscattering by a population of relativistic electrons treated in the twisted magnetosphere. Our code is specifically tailored to work in the ultra-magnetized regime; polarization and QED effects are consistently accounted for, as well different configurations for the magnetosphere. We discuss the predicted spectral properties in the 0.1–1000 keV range, the polarization properties, and we present the model application to a sample of magnetars soft X-ray spectra.     

Multi-wavelength study of the short term TeV flaring activity from the blazar Mrk 501 observed in June 2014

In this work, we study the short term flaring activity from the high synchrotron peaked blazar Mrk 501 detected by the FACT and H.E.S.S. telescopes in the energy range 2–20 TeV during June 23–24, 2014 (MJD 56831.86–56831.94). We revisit this major TeV flare of the source in the context of near simultaneous multi-wavelength observations of $\gamma$–rays in MeV-GeV regime with Fermi-LAT, soft X-rays in 0.3–10 keV range with Swift-XRT, hard X-rays in 10–20 keV and 15–50 keV bands with MAXI and Swift-BAT respectively, UV-Optical with Swift-UVOT and 15 GHz radio with OVRO telescope. We have performed a detailed temporal and spectral analysis of the data from Fermi-LAT, Swift-XRT and Swift-UVOT during the period June 15–30, 2014 (MJD 56823–56838). Near simultaneous archival data available from Swift-BAT, MAXI and OVRO telescope along with the V-band optical polarization measurements from SPOL observatory are also used in the study of giant TeV flare of Mrk 501 detected by the FACT and H.E.S.S. telescopes. No significant change in the multi-wavelength emission from radio to high energy $\gamma$–rays during the TeV flaring activity of Mrk 501 is observed except variation in soft X-rays. The varying soft X-ray emission is found to be correlated with the $\gamma$–ray emission at TeV energies during the flaring activity of the source. The soft X-ray photon spectral index is observed to be anti-correlated with the integral flux showing harder-when-brighter behavior. An average value of 4.5$\%$ for V-band optical polarization is obtained during the above period whereas the corresponding electric vector position angle changes significantly. We have used the minimum variability timescale from the H.E.S.S. observations to estimate the Doppler factor of the emission region which is found to be consistent with the previous studies of the source.     

The ROSAT all-sky survey

The ROSAT (Röntgensatellit) X-ray astronomy satellite has completed the first all-sky X-ray and XUV survey with imaging telescopes. About 60,000 new X-ray and 400 new XUV /1/ sources were detected. This contribution will deal with preliminary results from the ROSAT ALL-SKY X-RAY SURVEY. The ROSAT diffuse and point-source X-ray skymaps, the positional accuracy obtained for the X-ray sources, and a few results from correlations performed with available catalogues in various energy bands like the Radio, Infrared, Visible, UV, and hard X-rays as well as identifications from optical follow-up observations are presented.     

Physics of the impulsive phase of solar flares

The physics of the impulsive phase of solar flares is discussed in relation to high resolution microwave, hard X-ray and ultraviolet observations. High spatial resolution observations of the structure of microwave flaring loops and their interpretation in terms of arcades of loops as the sites of primary energy release are presented. Theoretical interpretation of the confinement of microwave producing energetic electrons in the coronal part of loops is discussed. High temporal and spatial resolution measurements in hard X-rays, as well as observations of the spectral evolution of the hard X-ray emission are presented. Observations of the relative locations of microwave and hard X-ray emitting regions are presented and their significance with respect to the energy release site and electron acceleration is discussed. The relative timing of the peaks of impulsive hard X-ray and microwave burst is discussed. The significance of ultraviolet measurements in obtaining the density of flaring regions is discussed. Possible diagnostics of impulsive phase onsets from cm-λ polarization data are presented, and the role of the emergence of new flux and of the current sheet formed between closed loops in producing impulsive energy release at centimeter wavelengths are analyzed. Decimeter and meter wave manifestations of preflash phase and millisecond pulsations at centimeter and decimeter wavelengths and the relevant physical processes involved are discussed.     

A question raised from the observation of dynamic cusp formation: When and where does particle acceleration occur?

We present observations of a C9.4 flare on 2002 June 2 in EUV (TRACE) and X-rays (RHESSI). The multiwavelength data reveal: (1) the involvement of a quadrupole magnetic configuration; (2) loop expansion and ribbon motion in the pre-impulsive phase; (3) gradual formation of a new compact loop with a long cusp at the top during the impulsive phase of the flare; (4) appearance of a large, twisted loop above the cusp expanding outward immediately after the hard X-ray peak; and (5) X-ray emission observed only from the new compact loop and the cusp. In particular, the gradual formation of an EUV cusp feature is very clear. The observations also reveal the timing of the cusp formation and particle acceleration: most of the impulsive hard X-rays (>25 keV) were emitted before the cusp was seen. This suggests that fast reconnection occurred during the restructuring of the magnetic configuration, resulting in more efficient particle acceleration, while the reconnection slowed after the cusp was completely formed and the magnetic geometry was stabilized. This observation is consistent with the observations obtained with Yohkoh/Soft X-ray Telescope (SXT) that soft X-ray cusp structures only appear after the major impulsive energy release in solar flares. These observations have important implications for the modeling of magnetic reconnection and particle acceleration.     

Analysis of the 1980 November 18 limb flare observed by the hard X-ray imaging spectrometer (HXIS)

X-ray images of the 18 November 1980 limb flare taken by the HXIS instrument aboard SMM were analysed. The hard X-rays originated from three spots on the SW limb of the solar disk with different altitudes and time evolution. The locations of the brightest spots in hard and soft X-rays are compared with the predictions of flare models. The X-ray spctra from the pixels with highest count rates can be fitted by power laws. The spatial variation of the spectral index is in agreement with the existence of a non-thermal electron component.     

The X-ray evolution of galaxies: implications for future X-ray observatories

The X-ray evolution of the luminosity of normal galaxies is primarily driven by the evolution of their X-ray binary populations. The imprints left by a cosmological evolution of the star formation rate (SFR) will cause the average X-ray luminosity of galaxies to appear higher in the redshift range 1–3. As reported by White and Ghosh [ApJ, 504 (1998) L31] the profile of X-ray luminosity with redshift can both serve as a diagnostic probe of the SFR profile and constrain evolutionary models for X-ray binaries. In order to observe the high redshift (z>3) universe in the X-ray band, it is necessary to avoid confusion from foreground field galaxies. We report on the predictions of these models of the X-ray flux expected from galaxies and the implications for the telescope parameters of future deep universe X-ray observatories.     

Hard X-ray source profiles as determined by RHESSI

The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) has been recording rotationally-modulated X-rays from solar flares since its launch on February 5, 2002. Its 9 grid pairs time-modulate the detected photon flux giving RHESSI spatial information on hard X-rays at 9 logarithmically-spaced angular scales ranging from 2.3 to 183 arcsec. Using the calibrated modulation profiles for a variety of flares, we present new information on the spatial profiles of the hard X-ray structures in flares. We find that the FWHM of cores of single-component flares range from 3 to 11″ in size. Most of the flares in this set show extended emission out to 2 to 3 times the radii of the cores, and these ‘halos’ contain up to 25% of the total flux.     

太阳耀斑硬X射线高能时延和辐射展宽

本文从耀斑高能电子束流与太阳大气相互作用产生硬X射线辐射的基本事实出发,根据观测资料,提出了一个流量与能谱同步变化的注入源函数模型,研究太阳大气(靶物质)密度对耀斑硬X射线时间响应.理论计算与观测事实基本一致.主要计算结果如下:高能时延与辐射展宽是耀斑硬X射线轫致辐射时间特征的二种表现,硬X射线发射区的太阳大气密度越低,高能时延与辐射展宽效应越明显,二者之间存在显著的相关性.      

Theoretical modelling of X-ray fluorescence signals for different lunar compositions and dependence on solar activity

We present a forward modelling technique for calculating the surface X-ray spectra for a variety of lunar terrains. Our calculations considered variations in solar fluxes from solar quiescent condition to large flare activity (M1 flare), and expected elemental concentrations in the target, as well as yield, instrumental, and viewing geometry parameters for X-ray induced fluorescence from the lunar surface. Additionally, we present estimates of anticipated XRF signals from prominent K_α lines observable by a collimated 14 cm² X-ray detector from a 100 km lunar orbit with ∼20 km spatial resolution. Our results show that Mg, Al and Si characteristic K_α lines can be observed for all solar conditions. The Ca K_α lines line can be differentiated from a fixed background during more energetic solar conditions such as C1 and M1 flares, whereas Ti and Fe lines are identifiable only during C1 and M1 solar flare conditions for Apollo 12 site composition. Both the K_α X-ray intensity ratios of Mg/Si and Al/Si correlate well with concentration ratios of Mg/Si and Al/Si, respectively, for B1 and M1 solar conditions. The K_α X-ray intensity ratios of Fe/Si and Ca/Si correlates with concentration ratios of Fe/Si and Ca/Si, respectively, for M1 solar condition. In principle, the modelling technique outlined here can be used to determine absolute elemental abundances (Mg, Al, Si, Ca, Ti and Fe) from X-ray spectra measured during recent and future lunar missions.     

Alpha Particle X-Ray Spectrometer (APXS) on-board Chandrayaan-2 rover

Alpha Particle X-ray Spectrometer (APXS) payload configuration for Chandrayaan-2 rover has been completed recently and fabrication of mechanical assembly, PCB layout design and fabrication are in progress. Here we present the design and performance evaluation of various subsystems developed for APXS payload. The low energy threshold of <1 keV and the energy resolution of ∼150 eV at 5.9 keV, for the Silicon Drift Detector (SDD), as measured from the developed APXS electronics is comparable to the standard spectrometers available off-the-shelf. We have also carried out experiments for measuring fluorescent X-ray spectrum from various standard samples from the USGS catalog irradiated by the laboratory X-ray source ²⁴¹Am with 1 mCi activity. It is shown that intensities of various characteristic X-ray lines are well correlated with the respective elemental concentrations.