Tsinghua Center for Astrophysics and the Dark Universe

2014 ◽  
Vol 03 (02) ◽  
pp. 63-70
Author(s):  
Charling Tao
Keyword(s):  
Gamma Rays ◽  
Nuclear Physics ◽  
Gamma Ray ◽  
High Energy ◽  
X Rays ◽  
High Energy Astrophysics ◽  
Research Directions ◽  
X Ray ◽  
Main Research ◽  
Optical Wavelengths

The Tsinghua Center for Astrophysics (THCA) was founded in 2001 by Prof. Li Tipei and Shang Rencheng. A distinguishing characteristic of THCA's astrophysics program is its emphasis on space X-ray and gamma-ray instrumentation, by taking advantage of Tsinghua's strong programs on nuclear physics, nuclear engineering, space and aeronautics engineering, as well as electronics and information technology. The main research directions in THCA include high energy astrophysics and cosmology with space and ground observations in X-rays and gamma-rays, and more recently in optical wavelengths, radio-astronomy, gravitational waves, dark matter and dark energy analyses and projects.

scholarly journals Centaurus A at Hard X-Rays and Soft Gamma-Rays

2010 ◽  
Vol 27 (4) ◽  
pp. 431-438 ◽  
Author(s):  
H. Steinle
Keyword(s):  
Energy Range ◽  
Spatial Resolution ◽  
Gamma Rays ◽  
Gamma Ray ◽  
Spectral Energy Distribution ◽  
High Energy ◽  
Spectral Energy ◽  
X Rays ◽  
Satellite Mission ◽  
X Ray

AbstractCen A, at a distance of less than 4 Mpc, is the nearest radio-loud AGN. Its emission is detected from radio to very-high energy gamma-rays. Despite the fact that Cen A is one of the best studied extragalactic objects the origin of its hard X-ray and soft gamma-ray emission (100 keV <E< 50 MeV) is still uncertain. Observations with high spatial resolution in the adjacent soft X-ray and hard gamma-ray regimes suggest that several distinct components such as a Seyfert-like nucleus, relativistic jets, and even luminous X-ray binaries within Cen A may contribute to the total emission in the MeV regime that has been detected with low spatial resolution. As the Spectral Energy Distribution of Cen A has its second maximum around 1 MeV, this energy range plays an important role in modeling the emission of (this) AGN. As there will be no satellite mission in the near future that will cover this energies with higher spatial resolution and better sensitivity, an overview of all existing hard X-ray and soft gamma-ray measurements of Cen A is presented here defining the present knowledge on Cen A in the MeV energy range.

scholarly journals Hot Accretion Disks and the High Energy Background

1983 ◽  
Vol 104 ◽  
pp. 345-346
Author(s):  
M. Kafatos ◽  
Jean A. Eilek
Keyword(s):  
Active Galactic Nuclei ◽  
Accretion Disks ◽  
Spectral Range ◽  
Gamma Rays ◽  
Gamma Ray ◽  
Galactic Nuclei ◽  
Seyfert Galaxies ◽  
High Energy ◽  
X Rays ◽  
X Ray

The origin of the high energy (X-ray and gamma-ray) background may be attributed to discrete sources, which are usually thought to be active galactic nuclei (AGN) (cf. Rothschild et al. 1982, Bignami et al. 1979). At X-rays a lot of information has been obtained with HEAO-1 in the spectral range 2–165 keV. At gamma-rays the background has been estimated from the Apollo 15 and 16 (Trombka et al. 1977) and SAS-2 (Bignami et al. 1979) observations. A summary of some of the observations (Rothschild et al. 1982) is shown in Figure 1. The contribution of AGN to the diffuse high energy background is uncertain at X-rays although it is generally estimated to be in the 20–30% range (Rothschild et al. 1982). At gamma-rays, in the range 1–150 MeV, AGN (specifically Seyfert galaxies) could account for all the emission.

scholarly journals Solar Hard X-Ray and Gamma-Ray Observations from GRANAT

1994 ◽  
Vol 142 ◽  
pp. 611-621
Author(s):  
N. Vilmer
Keyword(s):  
Gamma Rays ◽  
Solar Flares ◽  
Gamma Ray ◽  
Ground Level ◽  
High Energy ◽  
Angle Distribution ◽  
X Rays ◽  
X Ray ◽  
Electrons And Ions ◽  
Solar Bursts

AbstractHard X-rays and gamma-rays are the most direct signature of the energetic electrons and ions which are accelerated during solar flares. Since the beginning of 1990 the PHEBUS instrument and the SIGMA anticoincidence shield aboard GRANAT have provided hard X-ray and gamma-ray observations of solar bursts in the energy range 0.075-124 and 0.200-15 MeV, respectively. After a brief description of the experiments, we present some results obtained on solar bursts recorded in 1990 and 1991 June. Special emphasis is given to the results related with particle acceleration during solar flares.The first part of the review is devoted to the constraints obtained on the electron acceleration timescale through the analysis of the temporal characteristics of the bursts. Combined studies of hard X-ray and gamma-ray emissions from PHEBUS and radio emissions from the Nançay Multifrequency Radioheliograph are used to infer constraints on the coronal magnetic topology involved in flares. The characteristics (location, spectrum) of the radio-emitting sources are found to vary within a flare from one hard X-ray peak to the other. Hard X-ray and gamma-ray burst onsets and rapid increases of the > 10 MeV emission are coincident with changes in the associated radio emission pattern. These results will be discussed in the context of the flare energy release.The second part of the paper concerns the heliocentric angle distribution of > 10 MeV events and presents more detailed observations of some of the largest flares in the gamma-ray line and the high-energy domains produced by ultrarelativistic electrons and > 100 MeV nucleon−1 ions. The PHEBUS observations of the gamma-ray line flare of 11 June 1991 have been used to deduce the hardness of the accelerated ion spectrum. The link between the main part of the flare and the late long-lasting >50 MeV emission detected by EGRET/COMPTON is discussed. Finally some observations of the large 1990 May 24 flare which produced a large neutron event at ground level are presented.Subject headings: acceleration of particles — Sun: flares — Sun: radio radiation — Sun: X-rays, gamma rays

scholarly journals The Role of Ground-Based Robotic Observatories in Satellite Projects

2010 ◽  
Vol 2010 ◽  
pp. 1-10
Author(s):  
R. Hudec
Keyword(s):  
Gamma Rays ◽  
Large Fraction ◽  
High Energy ◽  
Photometric Data ◽  
X Rays ◽  
High Energy Astrophysics ◽  
Robotic Telescopes ◽  
Optical Wavelengths ◽  
Multispectral Analysis

We discuss the role of robotic telescopes in satellite projects, as well as related strategies. Most satellite projects in space astrophysics focus on high-energy astrophysics from X-rays to gamma-rays. A large fraction of objects of high-energy astrophysics emit also optical light, which is, in many cases, variable. The observation of these sources at optical wavelengths can provide valuable inputs for multispectral analysis of various categories of celestial high-energy (HE) sources. As the magnitudes of numerous objects are bright and can be hence accessed by robotic ground-based observatories, these observations can contribute to investigations and analyses of HE sources. We discuss in detail this possible contribution, with emphasis on the ESAINTEGRALmission. In addition to this, there are also satellite projects outside the high-energy astronomy, in which the robotic telescopes can also play an important role. We will illustrate this on the example of the ESA satelliteGaia. In this project, robotic telescopes are expected not only to verify the triggers detected by satellite (such as transients and flares) but also to provide additional (mostly photometric) data for better scientific cases.

The neutron, gamma-ray, X-ray spectrometer (NGXS): A compact instrument for making combined measurements of neutrons, gamma-rays, and X-rays

2014 ◽  
Vol 93 ◽  
pp. 524-529 ◽  
Author(s):  
David J. Lawrence ◽  
William C. Feldman ◽  
Robert E. Gold ◽  
John O. Goldsten ◽  
Ralph L. McNutt
Keyword(s):  
Gamma Rays ◽  
Gamma Ray ◽  
X Rays ◽  
X Ray ◽  
Combined Measurements

scholarly journals Physical Constraints on Models of Gamma-Ray Bursters

1986 ◽  
Vol 89 ◽  
pp. 305-321
Author(s):  
Richard I. Epstein
Keyword(s):  
Gamma Rays ◽  
Gamma Ray ◽  
High Energy ◽  
X Rays ◽  
Burst Source ◽  
Gamma Ray Burst ◽  
Physical Constraints ◽  
Low Energies ◽  
Energy Gamma ◽  
Photon Interactions

AbstractThe power per logarithmic bandwidth in gamma-ray burst spectra generally increases rapidly with energy through the x-ray range and does not cut off sharply above a few MeV. This spectral form indicates that a very small fraction of the energy from a gamma-ray burst source is emitted at low energies or is reprocessed into x-rays and that the high-energy gamma rays are not destroyed by photon-photon interactions. The implications are that the emission mechanism for the gamma-ray bursts is not synchrotron radiation from electrons that lose most of their energy before being re-accelerated and that either the regions from which the gamma rays are emitted are large compared to the size of a neutron star or the emission is collimated and beamed away from the stellar surface.

scholarly journals The Flare of 1989 September 9, 09:09 UT: Does Coronal Loop Collision Initiate Efficient Gamma-Ray Emission?

1994 ◽  
Vol 142 ◽  
pp. 707-711
Author(s):  
H. Aurass ◽  
A. Hofmann ◽  
E. Rieger
Keyword(s):  
Current Sheet ◽  
Gamma Rays ◽  
Coronal Loop ◽  
Gamma Ray ◽  
High Energy ◽  
X Rays ◽  
Subject Headings ◽  
Γ Ray ◽  
Gamma Ray Emission ◽  
Magnetogram Data

AbstractVector magnetogram data and Hα pictures together with data published by Chupp et al. lead us to conjecture that in the presented case a contact between the rising two-ribbon flare current sheet and a coronal loop connecting two nearby plage regions initiates efficient high-energy γ-ray emission.Subject headings: Sun: corona — Sun: flares — Sun: X-rays, gamma rays

scholarly journals Imaging in Hard X-ray Astronomy

2003 ◽  
Vol 214 ◽  
pp. 70-83 ◽  
Author(s):  
T. P. Li
Keyword(s):  
Gamma Ray ◽  
Signal To Noise Ratio ◽  
High Energy ◽  
High Signal ◽  
Wide Field ◽  
X Rays ◽  
X Ray ◽  
Energy Gamma ◽  
High Resolution Images ◽  
Energy Processes

The energy range of hard X-rays is a key waveband to the study of high energy processes in celestial objects, but still remains poorly explored. In contrast to direct imaging methods used in the low energy X-ray and high energy gamma-ray bands, currently imaging in the hard X-ray band is mainly achieved through various modulation techniques. A new inversion technique, the direct demodulation method, has been developed since early 90s. with this technique, wide field and high resolution images can be derived from scanning data of a simple collimated detector. The feasibility of this technique has been confirmed by experiment, balloon-borne observation and analyzing simulated and real astronomical data. Based the development of methodology and instrumentation, a high energy astrophysics mission – Hard X-ray Modulation Telescope (HXMT) has been proposed and selected in China for a four-year Phase-A study. The main scientific objectives are a full-sky hard X-ray (20–200 keV) imaging survey and high signal-to-noise ratio timing studies of high energy sources.

scholarly journals DIVISION D COMMISSION 44: SPACE AND HIGH-ENERGY ASTROPHYSICS

2015 ◽  
Vol 11 (T29A) ◽  
pp. 219-244
Author(s):  
Christine Jones ◽  
Noah Brosch ◽  
Günther Hasinger ◽  
Matthew G. Baring ◽  
Martin Adrian Barstow ◽  
...  
Keyword(s):  
Gamma Ray ◽  
Cosmic Ray ◽  
High Energy ◽  
High Energy Astrophysics ◽  
X Ray ◽  
Neutrino Detectors ◽  
Gamma Ray Astronomy ◽  
The Hague ◽  
Almost All ◽  
Modern Astronomy

Division XI, the predecessor to Division D until 2012, was formed in 1994 at the IAU General Assembly in The Hague by merging Commission 44 Astronomy from Space and Commission 48 High Energy Astrophysics. Historically, space astrophysics started with the high energy wavelengths (far UV, X-ray, and gamma-ray astronomy) which are only accessible from space. However, in modern astronomy, to study high energy astrophysical processes, almost all wavelengths are used (including gamma-ray, X-ray, UV, optical, infrared, submillimeter and radio). In addition other ground-based facilities, including gravitational wave antennas, neutrino detectors and high-energy cosmic ray arrays are joining in this era of multi-messenger astrophysics, as well as space missions with the primary goals to discover and study exoplanets, are under the umbrella of Division XI.

scholarly journals Design and Performance of the X-ray Polarimeter X-Calibur

2014 ◽  
Vol 03 (02) ◽  
pp. 1440008 ◽  
Author(s):  
M. Beilicke ◽  
F. Kislat ◽  
A. Zajczyk ◽  
Q. Guo ◽  
R. Endsley ◽  
...  
Keyword(s):  
Gamma Ray ◽  
Detection Efficiency ◽  
Grazing Incidence ◽  
High Energy ◽  
X Rays ◽  
Field Orientation ◽  
Synchrotron Source ◽  
X Ray ◽  
And Performance ◽  
Detector Assembly

X-ray polarimetry promises to give qualitatively new information about high-energy astrophysical sources, such as binary black hole systems, micro-quasars, active galactic nuclei, neutron stars, and gamma-ray bursts. We designed, built and tested a X-ray polarimeter, X-Calibur, to be used in the focal plane of the balloon-borne InFOCμS grazing incidence X-ray telescope. X-Calibur combines a low-Z scatterer with a Cadmium Zinc Telluride (CZT) detector assembly to measure the polarization of 20–80 keV X-rays making use of the fact that polarized photons scatter preferentially perpendicular to the electric field orientation. X-Calibur achieves a high detection efficiency of ≃80%. The X-Calibur detector assembly is completed, tested, and fully calibrated. The response to a polarized X-ray beam was measured successfully at the Cornell High Energy Synchrotron Source. This paper describes the design, calibration and performance of the X-Calibur polarimeter. In principle, a similar space-borne scattering polarimeter could operate over the broader 2–100 keV energy band.

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