arXiv subjects

Q. Guo

Publications and source records attributed to Q. Guo.

22 records · Page 2Linked to original sources

arXiv2011

Design and tests of the hard X-ray polarimeter X-Calibur

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, and gamma-ray bursts. We designed, built and tested a hard X-ray polarimeter X-Calibur to be used in the focal plane of the InFOCuS grazing incidence hard X-ray telescope. X-Calibur combines a low-Z Compton scatterer with a CZT detector assembly to measure the polarization of 10-80 keV X-rays making use of the fact that polarized photons Compton scatter preferentially perpendicular to the electric field orientation. X-Calibur achieves a high detection efficiency of order unity.

astro-ph.IM↗

arXiv2011

Study of Thick CZT Detectors for X-ray and Gamma-Ray Astronomy

CdZnTe (CZT) is a wide bandgap II-VI semiconductor developed for the spectroscopic detection of X-rays and γ-rays at room temperature. The Swift Burst Alert Telescope is using an 5240 cm2 array of 2 mm thick CZT detectors for the detection of 15-150 keV X-rays from Gamma-Ray Bursts. We report on the systematic tests of thicker (\geq 0.5 cm) CZT detectors with volumes between 2 cm3 and 4 cm3 which are potential detector choices for a number of future X-ray telescopes that operate in the 10 keV to a few MeV energy range. The detectors contacted in our laboratory achieve Full Width Half Maximum energy resolutions of 2.7 keV (4.5%) at 59 keV, 3 keV (2.5%) at 122 keV and 4 keV (0.6%) at 662 keV. The 59 keV and 122 keV energy resolutions are among the world-best results for \geq 0.5 cm thick CZT detectors. We use the data set to study trends of how the energy resolution depends on the detector thickness and on the pixel pitch. Unfortunately, we do not find clear trends, indicating that even for the extremely good energy resolutions reported here, the achievable energy resolutions are largely determined by the properties of individual crystals. Somewhat surprisingly, we achieve the reported results without applying a correction of the anode signals for the depth of the interaction. Measuring the interaction depths thus does not seem to be a pre-requisite for achieving sub-1% energy resolutions at 662 keV.

astro-ph.IM↗

arXiv2010

Scientific Prospects for Hard X-ray Polarimetry

X-ray polarimetry promises to give qualitatively new information about high-energy sources. Examples of interesting source classes are binary black hole systems, rotation and accretion powered neutron stars, Microquasars, Active Galactic Nuclei and Gamma-Ray Bursts. Furthermore, X-ray polarimetry affords the possibility for testing fundamental physics, e.g. to observe signatures of light bending in the strong gravitational field of a black hole, to detect third order Quantum Electrodynamic effects in the magnetosphere of Magnetars, and to perform sensitive tests of Lorentz Invariance. In this paper we discuss scientific drivers of hard (>10 keV) X-ray polarimetry emphasizing how observations in the hard band can complement observations at lower energies (0.1 - 10 keV). Subsequently, we describe four different technical realizations of hard X-ray polarimeters suitable for small to medium sized space borne missions, and study their performance in the signal-dominated case based on Monte Carlo simulations. We end with confronting the instrument requirements for accomplishing the science goals with the capabilities of the four polarimeters.

astro-ph.HE↗

arXiv2009

On the nuclear obscuration of H2O maser galaxies

To shed light onto the circumnuclear environment of 22 GHz H2O maser galaxies, we have analyzed some of their multi-wavelength properties, including the far infrared luminosity (FIR), the luminosity of the [O III]\lambda5007 emission line, the nuclear X-ray luminosity, and the equivalent width of the neutral iron Ka emission line (EW (Ka)). Our statistical analysis includes a total of 85 sources, most of them harboring an active galactic nucleus (AGN). There are strong anti-correlations between EW (Ka) and two "optical thickness parameters", i.e. the ratios of the X-ray luminosity versus the presumably more isotropically radiated [O III] and far infrared (FIR) luminosities. Based on these anti-correlations, a set of quantitative criteria, EW (Ka) > 300eV, L_{2-10keV} < 2L_[O III] and L_{FIR} > 600L_{2-10keV} can be established for Compton-thick nuclear regions. 18 H2O maser galaxies belong to this category. There are no obvious correlations between the EW (Ka), the [O III] luminosity and the isotropic H2O maser luminosity. When comparing samples of Seyfert 2s with and without detected H2O maser lines, there seem to exist differences in EW (Ka) and the fraction of Compton-thick nuclei. This should be studied further. For AGN masers alone, there is no obvious correlation between FIR and H2O maser luminosities. However, including masers associated with star forming regions, a linear correlation is revealed. Overall, the extragalactic FIR-H2O data agree with the corresponding relation for Galactic maser sources, extrapolated by several orders of magnitude to higher luminosities.

astro-ph.CO↗