High angular resolution astronomical observation in terahertz frequencies better than one milli-arcsecond will open a new field of terahertz astronomy. We propose terahertz intensity interferometry for aperture synthesis imaging. Fast photon detectors in terahertz frequencies are the key technology. We work on low leakage SIS photon detectors, which will be capable to detect every photon arrival. Photo response of SIS photon detectors is presented and its application to terahertz intensity interferometry is discussed together with developments of readout electronics and cryogenics.
Two types of field measurements on the Atacama Submillimeter Telescope Experiment 10-m antenna have been made to
diagnose antenna oscillations in strong wind gusts and to reduce pointing errors due to static/quasi-static wind loadings.
The measurements with seismic accelerometers on the reflector have been compared with those from axis angle encoders.
Our results have confirmed that the dominant wind effects are at low frequencies, and have found that twist and pitching
motion of yoke arms are the dominant source of pointing jitters and decrease with frequency along the Kolmogorov
slope of -5/3. In the range from about 1 to 10 Hz, the servo-loop excites and dominates pointing error oscillations. For
azimuth oscillations, the frontal wind has the largest effects, compared with side- or tail-wind. To improve pointing
performance against static/quasi-static wind effects, we have implemented and tested an auxiliary auto-pointingcorrection
system with a lookup table compiled from all-sky pointing measurements under strong winds, invoking the
Taylor's "frozen turbulence" hypothesis. We have successfully demonstrated that use of upwind data from a nearby
anemometer helps to reduce the pointing errors of static wind effects from 2.4 " rms (correction OFF) to 1.2 " rms
(correction ON) under a mean wind speed of 9.3 m s-1.
ASTE is a 10-m submillimeter telescope operating in Atacama desert in northern Chile since 2002 by NAOJ and
collaborators. Thanks to the excellent observing condition at the telescope site, ASTE has been producing numerous
astronomical results from star forming regions, Galactic center, Magellanic clouds, nearby galaxies, and galaxy clusters.
There has been three major improvements during the years 2007-2008: continuum camera "AzTEC", new SIS receiver
"CATS345", and a wide-band spectrometer "WHSF". AzTEC is a 144 element bolometer array at 270 GHz, developed
by University of Massachusetts and collaborators. The mapping speed reaches 10-30 arcmin2/hr/mJy2. CATS345 is a
side-band separation (2SB) SIS receiver developed by University of Tokyo and NAOJ. The IF bandwidth is 4 GHz with
side-band rejection ratio better than 10 dB. We have achieved the typical system noise temperature of 200-400 K (SSB)
within 330-360 GHz, the best value being 150 K (SSB) at the frequency of 12CO(J=3-2) at 345 GHz under a typical
weather condition. The new spectrometer WHSF employs of an FX type auto-correlator, ultra-high speed sampler, and
digital signal transmitter. It can be operated in two modes; 4096 MHz band-width × 2 IFs or 2048 MHz band-width × 4
IFs, both with 4096 channels in spectral resolution.
Because of the high transparency in infrared wavelength, Co. Chajnantor (5,650m altitude) at Atacama, Chile, is one of
the most promising sites for infrared astronomy in the world. For evaluating the site condition quantitatively we carried
out weather and cloud emissivity monitoring campaign from April 2006 to April 2007. The ground-level condition such
as wind direction, wind speed, air temperature, and humidity was monitored by a weather station installed at the
summit. Cloud emissivity was estimated by mid-infrared sky images taken by a whole-sky infrared camera every five
minutes for 24 hours a day, every day. Results are summarized as followings. 1) The weather condition at the summit is
slightly harsher than the condition at the Pampa la Bola plateau. Maximum speed of the wind is 35m/s, and minimum
temperature is about -10 degree. 2) Fraction of "clear+usable" weather (which is defined as the cloud emissivity < 10%)" is 82% in a year. The fraction decrease to 40-50% on Bolivian winter season, and increases to over 90% from
April to July. This is comparable or even better than the other astronomical sites.
SIS photon detectors are niobium-based superconducting direct detectors for submillimeter-wave that show superior performance when compared with bolometric detectors for ground-based observations. We present the design and development of the SIS photon detectors together with optical and cryogenic components for wide field continuum observation system on Atacama Submillimeter Telescope Experiment (ASTE). Using antenna coupled distributed junctions, SIS photon detectors give wide band response in a 650-GHz atmospheric window as well as high current sensitivity, shot noise limited operation, fast response and high dynamic range. Optical noise equivalent power (NEP) was measured to be 1.6x10-16 W/Hz0.5 that is less than the background photon fluctuation limit for ground based submillimeter-wave observations. Fabrication of focal plane array with 9 detector pixels is underway to install in ASTE.
Readout electronics with Si-JFETs operating at about 100 K will be used for this array. Development of readout electronics for larger array is based on GaAs-JFETs operating at 0.3 K. For the purpose of installing 100 element array of SIS photon detectors, we have developed remotely operable low-vibration cryostat, which now cools bolometers for 350, 450, 850-µm observations down to 0.34 K. GM-type 4-K cooler and He3/He4 sorption cooler is used, which can be
remotely recycled to keep detectors at 0.34 K. Since we have large optical window for this cryostat, sapphire cryogenic window is used to block infrared radiation. The sapphire window is ante-reflection coated with SiO2 by chemical vapor deposition (CVD). The transmittance of the cryogenic window at 650 GHz is more than 95%.
The National Astronomical Observatory of Japan has constructed a prototype 12-m antenna of the Atacama Compact Array to evaluate its performance at the ALMA Test Facility in the NRAO VLA observatory in New Mexico, the United States. The antenna has a CFRP tube backup structure (BUS) with CFRP boards to support 205 machined Aluminum
surface panels. Their accuracies were measured to be 5.9 m rms on average. A chemical treatment technique of the surface panels has successfully applied to scatter the solar radiation, which resulted in a subreflector temperature increase of about 25 degrees relative to ambient temperature during direct solar observations. Holography measurements and panel adjustments led to a final surface accuracy of 20 m rms, (weighted by 12dB edge taper), after three rounds of the panel adjustments. Based on a long term temperature monitoring of the BUS and thermal deformation FEM calculation, the BUS thermal deformation was estimated to be less than 3.1 m rms. We have employed gear drive mechanism both for a fast position switching capability and for smooth drive at low velocities. Servo errors measured with angle encoders were found to be less than 0.1 arcseconds rms at rotational velocities below 0.1 degrees s-1 and to increase to 0.7 arcseconds rms at the maximum speed of the 'on-the-fly' scan as a single dish, 0.5 deg s-1 induced by the irregularity of individual gear tooth profiles. Simultaneous measurements of the
antenna motion with the angle encoders and seismic accelerometers mounted at the primary reflector mirror edges and at the subreflector showed the same amplitude and phase of oscillation, indicating that they are rigid, suggesting that it is possible to estimate where the antenna is actually pointing from the encoder readout. Continuous tracking measurements of Polaris during day and night have revealed a large pointing drift due to thermal distortion of the yoke structure. We have applied retrospective thermal corrections to tracking data for two hours, with a preliminary thermal deformation model of the yoke, and have found the tracking accuracy improved to be 0.1 - 0.3 arcseconds rms for a 15-munites period. The whole sky absolute pointing error under no wind and during night was measured to be 1.17 arcseconds rms. We need to make both an elaborated modeling of thermal deformation of the structure and systematic searches for
significant correlation among pointing errors and metrology sensor outputs to achieve the stable tracking performance requested by ALMA.
ASTE (Atacama Submillimeter Telescope Experiment) is a project to install and operate a 10-m submillimeter telescope in the high altitude site (4,800 m) in Atacama desert, northern Chile. The project is aimed to explore the southern sky with submillimeter waves as well as to develop and evaluate various instruments and observing techniques. The telescope was shipped and re-assembled in Chilean site in early 2002, including the establishment of the on site infrastructure. Following evaluation of the telescope and receivers, scientific observations such as supernova remnants, galaxies, star forming regions and proto-planetary nebulae, have been carried out since early 2003. The high-precision 10-m antenna was measured to have the surface accuracy of 18.9 mm and the relative pointing accuracy was 1.2" r.m.s. for both azimuth and elevation. The subreflector is equipped with wobbling capability. Several types of receivers have been on board the telescope; the heterodyne-receivers operating at 100, 230, 345, 500 and 800 GHz bands including cartridge-type receivers, as well as a bolometer system covering 350, 650 and 850 GHz. The spectrometer is equipped with an XF type digital auto-correlator with four channels each covering up to 512 MHz with 1024 bins, which leads to 2 GHz coverage. The control system is designed to be capable of remote control from several sites via network connection, from the base facility at San Pedro de Atacama (2,400 m altitude) or even from Japan.
A 10-m submillimeter telescope designed for interferometric observations at bands from 3 to 0.3 mm has constructed at Nobeyama Radio Observatory. The telescope is an engineering model for a large millimeter and sub-millimeter array, and will be operated for developments of sub-millimeter observation techniques at a remote site. We have fabricated lightweight machined aluminum panels (15 kg m-2) that have a surface accuracy of 5 micrometer rms. They have a typical size of 0.8 m X 0.6 m, and are supported with three motorized screws. The back-up structure is constructed of a central hub of low thermal expansion alloy, and CFRP honeycomb boards and tubes. Holography measurements will be made with a nearby transmitter at 3 mm. The overall surface accuracy is expected to be < 25 micrometer rms; the goal being 17 micrometer rms. We have achieved an accuracy of 0.03' rms for angle encoders. The drive and control system is designed to achieve a pointing error of 1'.0 rms with no wind and at night. Under a wind velocity of 7 m s-1, the pointing error increases to 2'.0 rms. An optical telescope of 10-cm diameter mounted on the center hub will be used to characterize pointing and tracking accuracy. Thermal effects on the pointing and surface accuracy will be investigated using temperature measurements and FEM analyses. The fast position switching capability is also demanded to cancel atmospheric fluctuations. The antenna is able to drive both axes at a maximum velocity of 3 deg s-2 with a maximum acceleration of 6 deg. s-2. The telescope is currently equipped with SIS receivers for 100, 150, 230, and 345 GHz and a continuum backend and an FX-type digital autocorrelator with an instantaneous bandwidth of 512 MHz and 1024 channel outputs.
We are developing high quality reflector panels for the new 10-m telescope for millimeter/sub-millimeter waves, which is to be a prototype antenna for LMSA/ALMA. The telescope consists of 205 reflector panels, and is expected to achieve the surface accuracy of 17 micrometer for the entire telescope. Each reflector panels are machined from a single block of aluminum in size of 80 cm X 80 cm and weighs 15 kg/m2. The panel surface needs to be processed not to focus the sun-light on to the sub-reflector and the support structure to protect them from heating up. We have examined several methods for surface processing, including scratching the surface by a steel-wool or a sandpaper, and to blast sand like small particles against the panel surface. As a result, we found the sand-blast process to be the acceptable solution. The scattering width for the sun-lights were measured to be 86 degree(s) (FWHM), which feeds less than 1% of the incident sun- light to the sub-reflector, and causes temperature increase of only 45 degree(s)C. The sub-millimeter reflectivity of the sand- blasted panel was measured with the Fourier transform spectrometer which showed that the sand-blast process does not affect the reflectivity for the sub-millimeter waves up to 1.5 THz. The reflector panel mounted on the telescope is yet to be processed for scattering the sun-light in the near future.
The Hard x-ray Detector (HXD) is one of three instruments on the fifth Japanese x-ray astronomy satellite, Astro-E, scheduled for launch in 2000. The sensitivity of the Astro-E HXD will be higher by more than one order of magnitude than that of nay previous instrument between 10 keV and several 100 keV. The electronic system is designed to handle many independent data channels from the HXD within the limitation of size and power consumption required in Astro-E. In this paper, we will present the design and the preliminary performance of the processing electronic system.
We have developed the analog electronics of the ASTRO-E hard x-ray detector (HXD). The ASTRO-E is the fifth Japanese x-ray astronomy satellite scheduled for launch in 2000. Three experiments will be on board the satellite, one of which being the HXD. The detector consists of 16 units of well-type phoswich counters with silicon PIN diodes embedded therein, and covers the energy range of 10 approximately 600 keV with photon collecting area of about 350 cm2. The readout circuit for the HXD handles many signal channels (96 channels in total) under the limitation of power consumption and size set by the satellite. To meet the limitations, we have developed two types of bipolar semicustom LSIs. One is the pulse-shape discriminator (PSD-LSI) for phoswich counters and the other is for silicon PIN diodes (PIN-LSI). The PSD-LSI selects clean GSO hits and reduces the off-aperture x rays and internal background of the detector down to 10-5 c/s/cm2keV. One PIN-LSI handles signals from two PIN diodes, each consisting of an amplifier, a peak-hold circuit, and a comparator to trigger the readout system. Test pieces of these LSIs meet the specifications such as power consumptions and linearities. Using PIN-LSI, we could successfully obtain x-ray spectrum from 241Am with a PIN diode.
Astro-E is the x-ray satellite to be launched in the year 2000 by Inst. of Space & Astronautical Science. This report deals with the design and expected performance of the hard x-ray detector (HXD), one of the 3 experiments aboard Astro- E. The HXD is a combination of GSO/BGO well-type phoswich counters and silicon PIN diodes: the two combined will cover a wide energy band of 10 - 700 keV. The detector is characterized by its low background of approximately 10-5/s/cm2/keV and its sensitivity higher than any past missions between a few 10 keV and several 100 keV. Combined with the other 2 experiments, a micro-calorimeter array (XRS) and 4 CCD arrays (XIS), both with x-ray mirrors, the mission will cover the soft and hard x-ray range at a highest sensitivity.
The ASTRO-E satellite is scheduled for launch in 2000 by the Institute of Space and Astronautical Science (ISAS). In this paper the design and performance of the hard x ray detector (HXD) developed for ASTRO-E are described. The HXD is a combination of YAP/BGO phoswich scintillators and silicon PIN diodes covering a wide energy band of 10 - 700 keV. The detector background is reduced down to several times 10-6c/s/cm2/keV, and the sensitivity of the HXD is more than one order of magnitude higher than any other past missions in the range of a few 10 keV to several 100 keV. Thus ASTRO-E HXD is expected to achieve an extreme high performance for detecting cosmic hard x rays and low-energy gamma rays. Astrophysics to be explored with the HXT are expected to be extremely widespread and rich.
The fourth Japanese x-ray astronomy satellite, ASCA, carries two imaging gas scintillation proportional counters (GIS) on its focal plane. Extensive ground calibration has established its position resolution to be 0.5 mm and FWHM energy resolution to be 8.0% both at 6 keV. When combined with the x-ray telescope, a sensitivity range becomes 0.7 - 10 keV. These properties have been confirmed through in-orbit calibrations. The in-orbit background of the GIS has been confirmed to be as low as (5 - 7) X 10-4 c s-1cm-2keV-1 over the 1 - 10 keV range. The long-term detector gain is stable within a few % for two years. Gain dependence on the position and temperature has been calibrated down to 1%. The overall energy response is calibrated very accurately. Thus the GIS is working as an all-round cosmic x-ray detector.