60 research outputs found
Single Event Tolerance of X-ray SOI Pixel Sensors
We evaluate the single event tolerance of the X-ray silicon-on-insulator
(SOI) pixel sensor named XRPIX, developed for the future X-ray astronomical
satellite FORCE. In this work, we measure the cross-section of single event
upset (SEU) of the shift register on XRPIX by irradiating heavy ion beams with
linear energy transfer (LET) ranging from 0.022 MeV/(mg/cm2) to 68
MeV/(mg/cm2). From the SEU cross-section curve, the saturation cross-section
and threshold LET are successfully obtained to be and ,
respectively. Using these values, the SEU rate in orbit is estimated to be
0.1 event/year primarily due to the secondary particles induced by
cosmic-ray protons. This SEU rate of the shift register on XRPIX is negligible
in the FORCE orbit.Comment: 9 pages, 5 figures, accepted for publication in JATI
X-ray Radiation Damage Effects on Double-SOI Pixel Detectors for the Future Astronomical Satellite "FORCE"
We have been developing the monolithic active pixel detector "XRPIX" onboard
the future X-ray astronomical satellite "FORCE". XRPIX is composed of CMOS
pixel circuits, SiO2 insulator, and Si sensor by utilizing the
silicon-on-insulator (SOI) technology. When the semiconductor detector is
operated in orbit, it suffers from radiation damage due to X-rays emitted from
the celestial objects as well as cosmic rays. From previous studies, positive
charges trapped in the SiO2 insulator are known to cause the degradation of the
detector performance. To improve the radiation hardness, we developed XRPIX
equipped with Double-SOI (D-SOI) structure, introducing an additional silicon
layer in the SiO2 insulator. This structure is aimed at compensating for the
effect of the trapped positive charges. Although the radiation hardness to
cosmic rays of the D-SOI detectors has been evaluated, the radiation effect due
to the X-ray irradiation has not been evaluated. Then, we conduct an X-ray
irradiation experiment using an X-ray generator with a total dose of 10 krad at
the SiO2 insulator, equivalent to 7 years in orbit. As a result of this
experiment, the energy resolution in full-width half maximum for the 5.9 keV
X-ray degrades by 17.8 2.8% and the dark current increases by 89
13%. We also investigate the physical mechanism of the increase in the dark
current due to X-ray irradiation using TCAD simulation. It is found that the
increase in the dark current can be explained by the increase in the interface
state density at the Si/SiO2 interface.Comment: 15 pages, 12 figures, accepted for publication in Journal of
Astronomical Telescopes, Instruments, and System
First-year Sloan Digital Sky Survey-II (SDSS-II) Supernova Results: Hubble Diagram and Cosmological Parameters
We present measurements of the Hubble diagram for 103 Type Ia supernovae
(SNe) with redshifts 0.04 < z < 0.42, discovered during the first season (Fall
2005) of the Sloan Digital Sky Survey-II (SDSS-II) Supernova Survey. These data
fill in the redshift "desert" between low- and high-redshift SN Ia surveys. We
combine the SDSS-II measurements with new distance estimates for published SN
data from the ESSENCE survey, the Supernova Legacy Survey, the Hubble Space
Telescope, and a compilation of nearby SN Ia measurements. Combining the SN
Hubble diagram with measurements of Baryon Acoustic Oscillations from the SDSS
Luminous Red Galaxy sample and with CMB temperature anisotropy measurements
from WMAP, we estimate the cosmological parameters w and Omega_M, assuming a
spatially flat cosmological model (FwCDM) with constant dark energy equation of
state parameter, w. For the FwCDM model and the combined sample of 288 SNe Ia,
we find w = -0.76 +- 0.07(stat) +- 0.11(syst), Omega_M = 0.306 +- 0.019(stat)
+- 0.023(syst) using MLCS2k2 and w = -0.96 +- 0.06(stat) +- 0.12(syst), Omega_M
= 0.265 +- 0.016(stat) +- 0.025(syst) using the SALT-II fitter. We trace the
discrepancy between these results to a difference in the rest-frame UV model
combined with a different luminosity correction from color variations; these
differences mostly affect the distance estimates for the SNLS and HST
supernovae. We present detailed discussions of systematic errors for both
light-curve methods and find that they both show data-model discrepancies in
rest-frame -band. For the SALT-II approach, we also see strong evidence for
redshift-dependence of the color-luminosity parameter (beta). Restricting the
analysis to the 136 SNe Ia in the Nearby+SDSS-II samples, we find much better
agreement between the two analysis methods but with larger uncertainties.Comment: Accepted for publication by ApJ
The Sloan Digital Sky Survey-II Supernova Survey: Search Algorithm and Follow-up Observations
The Sloan Digital Sky Survey-II Supernova Survey has identified a large
number of new transient sources in a 300 sq. deg. region along the celestial
equator during its first two seasons of a three-season campaign. Multi-band
(ugriz) light curves were measured for most of the sources, which include solar
system objects, Galactic variable stars, active galactic nuclei, supernovae
(SNe), and other astronomical transients. The imaging survey is augmented by an
extensive spectroscopic follow-up program to identify SNe, measure their
redshifts, and study the physical conditions of the explosions and their
environment through spectroscopic diagnostics. During the survey, light curves
are rapidly evaluated to provide an initial photometric type of the SNe, and a
selected sample of sources are targeted for spectroscopic observations. In the
first two seasons, 476 sources were selected for spectroscopic observations, of
which 403 were identified as SNe. For the Type Ia SNe, the main driver for the
Survey, our photometric typing and targeting efficiency is 90%. Only 6% of the
photometric SN Ia candidates were spectroscopically classified as non-SN Ia
instead, and the remaining 4% resulted in low signal-to-noise, unclassified
spectra. This paper describes the search algorithm and the software, and the
real-time processing of the SDSS imaging data. We also present the details of
the supernova candidate selection procedures and strategies for follow-up
spectroscopic and imaging observations of the discovered sources.Comment: Accepted for publication in The Astronomical Journal (66 pages, 13
figures); typos correcte
First-Year Spectroscopy for the SDSS-II Supernova Survey
This paper presents spectroscopy of supernovae discovered in the first season
of the Sloan Digital Sky Survey-II Supernova Survey. This program searches for
and measures multi-band light curves of supernovae in the redshift range z =
0.05 - 0.4, complementing existing surveys at lower and higher redshifts. Our
goal is to better characterize the supernova population, with a particular
focus on SNe Ia, improving their utility as cosmological distance indicators
and as probes of dark energy. Our supernova spectroscopy program features
rapid-response observations using telescopes of a range of apertures, and
provides confirmation of the supernova and host-galaxy types as well as precise
redshifts. We describe here the target identification and prioritization, data
reduction, redshift measurement, and classification of 129 SNe Ia, 16
spectroscopically probable SNe Ia, 7 SNe Ib/c, and 11 SNe II from the first
season. We also describe our efforts to measure and remove the substantial host
galaxy contamination existing in the majority of our SN spectra.Comment: Accepted for publication in The Astronomical Journal(47pages, 9
figures
The Sloan Digital Sky Survey-II: Photometry and Supernova Ia Light Curves from the 2005 data
We present ugriz light curves for 146 spectroscopically confirmed or
spectroscopically probable Type Ia supernovae from the 2005 season of the
SDSS-II Supernova survey. The light curves have been constructed using a
photometric technique that we call scene modelling, which is described in
detail here; the major feature is that supernova brightnesses are extracted
from a stack of images without spatial resampling or convolution of the image
data. This procedure produces accurate photometry along with accurate estimates
of the statistical uncertainty, and can be used to derive photometry taken with
multiple telescopes. We discuss various tests of this technique that
demonstrate its capabilities. We also describe the methodology used for the
calibration of the photometry, and present calibrated magnitudes and fluxes for
all of the spectroscopic SNe Ia from the 2005 season
Discovery of an Unusual Optical Transient with the Hubble Space Telescope
We present observations of SCP 06F6, an unusual optical transient discovered during the Hubble Space Telescope Cluster Supernova Survey. The transient brightened over a period of ~;;100 days, reached a peak magnitude of ~;;21.0 in both i_775 and z_850, and then declined over a similar timescale. There is no host galaxy or progenitor star detected at the location of the transient to a 3 sigma upper limit of i_775 = 26.4 and z_850 = 26.1, giving a corresponding lower limit on the flux increase of a factor of ~;;120. Multiple spectra show five broad absorption bands between 4100 AA and 6500 AA and a mostly featureless continuum longward of 6500 AA. The shape of the lightcurve is inconsistent with microlensing. The transient's spectrum, in addition to being inconsistent with all known supernova types, is not matched to any spectrum in the Sloan Digital Sky Survey (SDSS) database. We suggest that the transient may be one of a new class
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