38 research outputs found
Discovery of a Compact X-ray Source in the LMC Supernova Remnant N23 with Chandra
An X-ray compact source was discovered with Chandra in a supernova remnant
(SNR) N23, located in the Large Magellanic Cloud. The compact source (CXOU
J050552.3-680141) is seen in only the hard band (> 2 keV) image of N23, while
the soft band image (< 2 keV) shows diffuse emission of the SNR, with an extent
of ~60 arcsec times ~80 arcsec. The compact source is located at almost the
center of N23, and there is no identifiable object for the source from previous
observations at any other wavelength. The source spectrum is best explained by
a power-law model with a photon index of 2.2 (1.9-2.7) and an
absorption-corrected luminosity of 1.0 x 10^34 ergs s^-1 in the 0.5--10 keV
band for a distance of 50 kpc. Neither pulsation nor time variability of the
source was detected with this observation with a time resolution of 3.2 sec.
These results correspond with those of Hughes et al. (2006) who carried out
analysis independently around the same time as our work. Based on information
from the best-fit power-law model, we suggest that the source emission is most
likely from a rotation-powered pulsar and/or a pulsar wind nebula. It is
generally inferred that the progenitor of N23 is a core-collapsed massive star.
Based on information from the best-fit power-law model, we suggest that the
source emission is most likely from a rotation-powered pulsar and/or a pulsar
wind nebula. It is generally inferred that the progenitor of N23 is a
core-collapsed massive star.Comment: 16 pages, 5 figures, 1 table, Accepted to Ap
Fine-pitch and thick-foil gas electron multipliers for cosmic x-ray polarimeters
We have produced various gas electron multiplier foils (GEMs) by using laser etching technique for cosmic X-ray polarimeters. The finest structure GEM we have fabricated has 30 μm-diameter holes on a 50 μm-pitch. The effective gain of the GEM reaches around 5000 at the voltage of 570 V between electrodes. The gain is slightly higher than that of the CERN standard GEM with 70 μm-diameter holes on a 140 μm-pitch. We have fabricated GEMs with thickness of 100 μm which has two times thicker than the standard GEM. The effective gain of the thick-foil GEM is 104 at the applied voltage of 350 V per 50 μm of thickness. The gain is about two orders higher than that of the standard GEM. The remarkable characteristic of the thick-foil GEM is that the effective gain at the beginning of micro-discharge is quite improved. For fabricating the thick-foil GEMs, we have employed new material, liquid crystal polymer (LCP) which has little moisture absorption rate, as an insulator layer instead of polyimide. One of the thick-foil GEM we have fabricated has 8 μm copper layer in the middle of the 100 μm-thick insulator layer. The metal layer in the middle of the foil works as a field-shaper in the multiplication channels, though it slightly decreases the effective gain
Suzaku Observation of the Metallicity in the Interstellar Medium of NGC 4258
The Suzaku X-ray satellite observed the nearby spiral galaxy NGC 4258 for a
total good exposure time of 100 ks. We present an analysis of the Suzaku XIS
data, in which we confirm that the 0.5--2 keV spectra of the interstellar
medium (ISM) are well-represented by a two-temperature model. The cool and hot
ISM temperatures are 0.23+-0.02 and 0.59 +-0.01 keV, respectively. Suzaku's
excellent spectral sensitivity enables us to measure the metal abundances of O,
Ne, Mg, Si and Fe of the ISM for the first time. The resultant abundance
pattern of O, Mg, Si, and Fe is consistent with that of the new solar abundance
table of Lodders (2003), rather than Anders & Grevesse (1989). This suggests
that the metal enrichment processes of NGC 4258 and of our Galaxy are similar.Comment: 9 pages, 4 figure
Development of cosmic x-ray polarimeter
We present a performance study of a cosmic X-ray polarimeter which is based on the photoelectric effect in gas, and sensitive to a few to 30 keV range. In our polarimeter, the key device would be the 50 μm pitch Gas Electron Multiplier (GEM). We have evaluated the modulation factor using highly polarized X-ray, provided by a synchrotron accelerator. In the analysis, we selected events by the eccentricity of the charge cloud of the photoelectron track. As a result, we obtained the relationship between the selection criteria for the eccentricity and the modulation factors; for example, when we selected the events which have their eccentricity of > 0.95, the polarimeter exhibited with the modulation factor of 0.32. In addition, we estimated the Minimum Detectable Polarization degree (MDP) of Crab Nebula with our polarimeter and found 10 ksec observation is enough to detect the polarization, if we adopt suitable X-ray mirrors
Development of Thick-foil and Fine-pitch GEMs with a Laser Etching Technique
We have produced thick-foil and fine-pitch gas electron multipliers (GEMs)
using a laser etching technique. To improve production yield we have employed a
new material, Liquid Crystal Polymer, instead of polyimide as an insulator
layer. The effective gain of the thick-foil GEM with a hole pitch of 140 um, a
hole diameter of 70 um, and a thickness of 100 um reached a value of 10^4 at an
applied voltage of 720 V. The measured effective gain of the thick-foil and
fine-pitch GEM (80 um pitch, 40 um diameter, and 100 um thick) was similar to
that of the thick-foil GEM. The gain stability was measured for the thick-foil
and fine-pitch GEM, showing no significant increase or decrease as a function
of elapsed time from applying the high voltage. The gain stability over 3 h of
operation was about 0.5%. Gain mapping across the GEM showed a good uniformity
with a standard deviation of about 4%. The distribution of hole diameters
across the GEM was homogeneous with a standard deviation of about 3%. There was
no clear correlation between the gain and hole diameter maps.Comment: 21 pages, 9 figure
X-Ray Measured Dynamics of Tycho's Supernova Remnant
We present X-ray proper-motion measurements of the forward shock and
reverse-shocked ejecta in Tycho's supernova remnant, based on three sets of
archival Chandra data taken in 2000, 2003, and 2007. We find that the proper
motion of the edge of the remnant (i.e., the forward shock and protruding
ejecta knots) varies from 0".20 yr^{-1} (expansion index m=0.33, where R = t^m)
to 0".40 yr^{-1} (m=0.65) with azimuthal angle in 2000-2007 measurements, and
0".14 yr^{-1} (m=0.26) to 0".40 yr^{-1} (m=0.65) in 2003-2007 measurements. The
azimuthal variation of the proper motion and the average expansion index of
~0.5 are consistent with those derived from radio observations. We also find
proper motion and expansion index of the reverse-shocked ejecta to be
0".21-0".31 yr^{-1} and 0.43-0.64, respectively. From a comparison of the
measured m-value with Type Ia supernova evolutionary models, we find a
pre-shock ambient density around the remnant of <~0.2 cm^{-3}
Expansion Velocity of Ejecta in Tycho's Supernova Remnant Measured by Doppler Broadened X-ray Line Emission
We show that the expansion of ejecta in Tycho's supernova remnant (SNR) is
consistent with a spherically symmetric shell, based on Suzaku measurements of
the Doppler broadened X-ray emission lines. All the strong K_alpha line
emission show broader widths at the center than at the rim, while the centroid
energies are constant across the remnant (except for Ca). This is the pattern
expected for Doppler broadening due to expansion of the SNR ejecta in a
spherical shell. To determine the expansion velocities of the ejecta, we
applied a model for each emission line feature having two Gaussian components
separately representing red- and blue-shifted gas, and inferred the Doppler
velocity difference between these two components directly from the fitted
centroid energy difference. Taking into account the effect of projecting a
three-dimensional shell to the plane of the detector, we derived average
spherical expansion velocities independently for the K_alpha emission of Si, S,
Ar, and Fe, and K_beta of Si. We found that the expansion velocities of Si, S,
and Ar ejecta of 4700+/-100 km/s are distinctly higher than that obtained from
Fe K_alpha emission, 4000+/-300 km/s, which is consistent with segregation of
the Fe in the inner ejecta. Combining the observed ejecta velocities with the
ejecta proper-motion measurements by Chandra, we derived a distance to the
Tycho's SNR of 4+/-1 kpc.Comment: Accepted to Apj, 25 pages, 7 figures, 5 table
Development of Resistive Electrode Gas Electron Multiplier (RE-GEM)
We successfully produced Resistive-Electrode Gas Electron Multiplier (RE-GEM) which has resistive electrodes instead of the metal ones which are employed for the standard GEM foils. RE-GEM has a resistive electrode of 25 micron-thick and an insulator layer of 100 micron-thick. The hole structure of RE-GEM is a single conical with the wider and narrower hole diameters of 80 micron and 60 micron, respectively. A hole pitch of RE-GEM is 140 micron. We obtained the maximum gain of about 600 and the typical energy resolution of about 20% (FWHM) at an applied voltage between the resistive electrodes of 620 V, using a collimated 8 keV X-rays from a generator in a gas mixture of 70% Ar and 30% CO2 by volume at the atmospheric pressure. We measured the effective gain as a function of the electric field of the drift region and obtained the maximum gain at an drift field of 0.5 kV/cm