arXiv subjects

Chih-Hsun Lin

Publications and source records attributed to Chih-Hsun Lin.

24 records · Page 2Linked to original sources

arXiv2019

Concept study of a small Compton polarimeter to fly on a CubeSat

Application of cubesats in astronomical observations has been getting more and more mature in recent years. Here we report a concept study of a small Compton polarimeter to fly on a cubesat for observing polarization of soft gamma-rays from a black-hole X-ray binary, Cygnus X-1. Polarization states provide very useful diagnostics on the emission mechanism and the origin of those gamma rays. In our study, we conducted Monte Carlo simulations to decide the basic design of this small polarimeter. Silicon detectors and cerium bromide scintillators were employed in this study. We estimated its on-axis Compton efficiency at different energies and its data telemetry requirement when flying in a low earth orbit. Our results indicate that it is feasible to achieve high signal-to-noise ratio for observing Cyg X-1 with such a small instrument. Based on this study, we will proceed to have a more realistic design and look for opportunities of a cubesat space mission.

astro-ph.IM↗

arXiv2017

Polarimetric Analysis of the Long Duration Gamma Ray Burst GRB 160530A With the Balloon Borne Compton Spectrometer and Imager

A long duration gamma-ray burst, GRB 160530A, was detected by the Compton Spectrometer and Imager (COSI) during the 2016 COSI Super Pressure Balloon campaign. As a Compton telescope, COSI is inherently sensitive to the polarization of gamma-ray sources in the energy range 0.2-5.0 MeV. We measured the polarization of GRB 160530A using 1) a standard method (SM) based on fitting the distribution of azimuthal scattering angles with a modulation curve, and 2) an unbinned, maximum likelihood method (MLM). In both cases, the measured polarization level was below the $99\%$ confidence minimum detectable polarization levels of $72.3 \pm 0.8\%$ (SM) and $57.5 \pm 0.8\%$ (MLM). Therefore, COSI did not detect polarized gamma-ray emission from this burst. Our most constraining $90\%$ confidence upper limit on the polarization level was $46\%$ (MLM).

astro-ph.HE↗

arXiv2017

Maximum Likelihood Compton Polarimetry with the Compton Spectrometer and Imager

Astrophysical polarization measurements in the soft gamma-ray band are becoming more feasible as detectors with high position and energy resolution are deployed. Previous work has shown that the minimum detectable polarization (MDP) of an ideal Compton polarimeter can be improved by $\sim 21\%$ when an unbinned, maximum likelihood method is used instead of the standard approach of fitting a sinusoid to a histogram of azimuthal scattering angles. Here we outline a procedure for implementing this maximum likelihood approach for real, non-ideal polarimeters. As an example, we use the recent observation of GRB 160530A with the Compton Spectrometer and Imager. We find that the MDP for this observation is reduced by $20\%$ when the maximum likelihood method is used instead of the standard method.

astro-ph.IM↗

arXiv2017

The 2016 Super Pressure Balloon flight of the Compton Spectrometer and Imager

The Compton Spectrometer and Imager (COSI) is a balloon-borne, soft-gamma ray imager, spectrometer, and polarimeter with sensitivity from 0.2 to 5 MeV. Utilizing a compact Compton telescope design with twelve cross-strip, high-purity germanium detectors, COSI has three main science goals: study the 511 keV positron annihilation line from the Galactic plane, image diffuse emission from stellar nuclear lines, and perform polarization studies of gamma-ray bursts and other extreme astrophysical environments. COSI has just completed a successful 46-day flight on NASA's new Super Pressure Balloon, launched from Wanaka, New Zealand, in May 2016. We present an overview of the instrument and the 2016 flight, and discuss COSI's main science goals, predicted performance, and preliminary results.

astro-ph.IM↗

arXiv2017

Benchmarking COSI's detector effects engine

The Compton Spectrometer and Imager (COSI) is a balloon-borne gamma-ray (0.2-5 MeV) telescope with inherent sensitivity to polarization. COSI's main goal is to study astrophysical sources such as $γ$-ray bursts, positron annihilation, Galactic nucleosynthesis, and compact objects. COSI employs a compact Compton telescope design utilizing 12 high-purity cross strip germanium detectors (size: $8\times8\times1.5$ cm$^3$, 2 mm strip pitch). We require well-benchmarked simulations to simulate the full instrument response used for data analysis, to optimize our analysis algorithms, and to better understand our instrument and the in-flight performance. In order to achieve a reasonable agreement, we have built a comprehensive mass model of the instrument and developed a detailed detector effects engine, which takes into account the individual performance of each strip as well as the characteristics of the overall detector system. We performed detailed Monte-Carlo simulations with Cosima/Geant4, applied the detector effects engine, and benchmarked the results with pre-flight calibrations using radioactive sources. After applying the detector effects engine, the simulations closely resemble the measurements, and the standard calibration, event reconstruction, and imaging pipeline used for measurements can also be applied to the simulations. In this manuscript, we will describe the detector effects engine, the benchmarking tests with calibrations, and the application to preliminary results from COSI's 46-day balloon flight in 2016.

astro-ph.IM↗

arXiv2010

Experimental and Theoretical Evidence for Extended Particle Models

We review the experimental searches on those interactions where the fundamental particles could exhibit a non point-like behavior. In particular we focus on the QED reaction measuring the differential cross sections for the process $ \EEGG $ at energies from sqrt{s} =55 GeV to 207 GeV using the data collected with the VENUS, TOPAZ, ALEPH, DELPHI L3 and OPAL from 1989 to 2003. The global fit to the data is 5 standard deviations away from the standard model expectation for the hypothesis of an excited state of the electron, corresponding to the cut-off scale Lambda =12.5 TeV. Assuming that this cut-off scale restricts the characteristic size of QED interaction to 15.7x10^{-18} cm, we perform an effort to assign in a semi-mechanical way all available properties of fundamental particles to a hypothetical classical object. Such object can be modeled as a classical gyroscope consisted of a non rotating inner massive kernel surrounded by an outer rotating massive layer equipped with charged sorted in a way to match the charge contents for different interactions. The model size of an electron agrees with 1.86x10^{-17} cm with the experiment. The introduction of a particle like structure related to gravity allows to estimate the inner mass kernel of an electron to 1.7x10^{-19} cm and the mass of a scaler to 154 GeV. The extension of the model to electrical charged particle-like structure in nonlinear electrodynamics coupled to General Relativity confirms the model in the global geometrical structure of mass and field distribution.

hep-ph↗