We present a systematic investigation of the gain properties of a gas electron multiplier (GEM) foil in pure dimethyl ether (DME) at low pressures. The GEM is made from copper- clad liquid crystal polymer insulator (LCP-GEM) designed for space use, a
nd is applied to a time projection chamber filled with low-pressure DME gas to observe the linear polarization of cosmic X-rays. We have measured gains of a 100 um-thick LCP-GEM as a function of the voltage between GEM electrodes at various gas pressures ranging from 10 to 190 Torr with 6.4 keV X-rays. The highest gain at 190 Torr is about 2x10^4, while that at 20 Torr is about 500. We find that the pressure and electric-field dependence of the GEM gain is described by the first Townsend coefficient. The energy scale from 4.5 to 8.0 keV is linear with non-linearity of less than 1.4% above 30 Torr.
Tychos supernova remnant was observed by the XIS and HXD instruments onboard the Suzaku satellite on 2006 June 26-29 for 92 ks. The spectrum up to 30 keV was well fitted with a two-component model, consisting of a power-law with photon index of 2.7 a
nd a thermal bremsstrahlung model with temperature of 4.7 keV. The former component can alternatively be modeled as synchrotron emission from a population of relativistic electrons with an estimated roll-off energy of around 1 keV. In the XIS spectra, in addition to the prominent Fe K_alpha line (6.445 keV), we observe for the first time significant K_alpha line emission from the trace species Cr and Mn at energies of 5.48 keV and 5.95 keV, respectively. Faint K_beta lines from Ca (4.56 keV) and Fe (7.11 keV) are also seen. The ionization states of Cr and Mn, based on their line centroids, are estimated to be similar to that of Fe K_alpha (Fe XV or XVI).
