The Greenland Telescope Project (GLT) has successfully commissioned its 12-m sub-millimeter. In January 2018, the fringes were detected between the GLT and the Atacama Large Millimeter Array (ALMA) during a very-long-baseline interferometry (VLBI) exercise. In April 2018, the telescope participated in global VLBI science observations at Thule Air Base (TAB). The telescope has been completely rebuilt, with many new components, from the ALMA NA (North America) Prototype antenna and equipped with a new set of sub-millimeter receivers operating at 86, 230, and 345 GHz, as well as a complete set of instruments and VLBI backends. This paper describes our progress and status of the project and its plan for the coming decade.
The Greenland Telescope completed its construction, so the commissioning phase has been started since December 2017. Single-dish commissioning has started from the optical pointing which produced the first pointing model, followed by the radio pointing and focusing using the Moon for both the 86 GHz and the 230 GHz receivers. After Venus started to rise from the horizon, the focus positions has been improved for both receivers. Once we started the line pointing using the SiO(2-1) maser line and the CO(2-1) line for the 86 GHz and the 230 GHz receivers, respectively, the pointing accuracy also improved, and the final pointing accuracy turned to be around 3" - 5" for both receivers. In parallel, VLBI commissioning has been performed, with checking the frequency accuracy and the phase stability for all the components that would be used for the VLBI observations. After all the checks, we successfully joined the dress rehearsals and actual observations of the 86 GHz and 230 GHz VLBI observations, The first dress rehearsal data between GLT and ALMA were correlated, and successfully detected the first fringe, which confirmed that the GLT commissioning was successfully performed.
NASA's Chandra X-Ray Observatory, designed for three years of operation with a goal of five years, is now entering its 15-th year of operation. Thanks to its superb angular resolution, the Observatory continues to yield new and exciting results, many of which were totally unanticipated prior to launch. We discuss the current technical status, review some recent scientific highlights, indicate a few future directions, and present what we are the most important lessons learned from our experience of building and operating this great observatory.
High-energy astrophysics is a relatively young scientific field, made possible by space-borne telescopes. During the
half-century history of x-ray astronomy, the sensitivity of focusing x-ray telescopes-through finer angular resolution
and increased effective area-has improved by a factor of a 100 million. This technological advance has enabled
numerous exciting discoveries and increasingly detailed study of the high-energy universe-including accreting (stellarmass
and super-massive) black holes, accreting and isolated neutron stars, pulsar-wind nebulae, shocked plasma in
supernova remnants, and hot thermal plasma in clusters of galaxies. As the largest structures in the universe, galaxy
clusters constitute a unique laboratory for measuring the gravitational effects of dark matter and of dark energy. Here,
we review the history of high-resolution x-ray telescopes and highlight some of the scientific results enabled by these
telescopes. Next, we describe the planned next-generation x-ray-astronomy facility-the International X-ray
Observatory (IXO). We conclude with an overview of a concept for the next next-generation facility-Generation X.
The scientific objectives of such a mission will require very large areas (about 10000 m2) of highly-nested lightweight
grazing-incidence mirrors with exceptional (about 0.1-arcsecond) angular resolution. Achieving this angular resolution
with lightweight mirrors will likely require on-orbit adjustment of alignment and figure.
Generation-X is required to be an X-ray observatory with 50 m2 effective collecting area and 0.1 arcsec half-power
diameter (HPD) angular resolution at 1 keV. It is conceived that a launch vehicle such as that studied for the
Ares V will carry a monolithic 16-m-diameter mirror to the earth-sun L2 point. Even with such a vehicle, the
reflectors comprising the ≈ 250 nested shells must be extremely light-weight. Therefore their figure and alignment
cannot be achieved on the ground, and likely could not be maintained through the launch environment. We
will present a conceptual solution to those constraints: adjustable X-ray optics, as a case of "adaptive" optics
where the stability once in orbit should require adjustments no more frequently than yearly. The figure would
be adjusted via thin-film actuators deposited directly to the back (non-reflecting) side of each element. This
bi-morph configuration would impart in-plane strains via the piezoelectric or electrostrictive effect. Requirements
of the adjustment are to the order of a few nanometer precision. Each shell, and each module, must also be
aligned, to tolerances of about 0.1 micrometer. We conceive that on-orbit data would be acquired by a built-in
Hartmann system for the alignment adjustments and low-order figure, and by ring profile measurements of a
very bright celestial X-ray source to correct figure errors up to the mid-frequency range of several hundredths
NASA's planned Ares V cargo launch vehicle with its 10 m diameter fairing and ~60,000 kg payload mass to L2 offers
the potential to launch entirely new classes of missions, such as 8-m monolithic aperture telescopes, 12- to 16-m aperture
x-ray telescopes, 16- to 24-m segmented telescopes and highly capable outer planet missions. This paper summarizes
the current Ares V baseline performance and reviews potential mission concepts enabled by these capabilities.
Generation-X will be an X-ray observatory with 50 m2
collecting area at 1 keV and 0.1" angular resolution. A key
concept to enable such a dramatic improvement in angular resolution is
that the mirror figure will be adjusted on-orbit; e.g., via piezo-electric
actuators deposited on the back side of very thin glass and imparting
strains in a bi-morph configuration. To make local adjustments to the
individual mirror shells we must employ an imaging detector far
forward of the focal surface, so that rays from the individual shells
can be measured as distinct rings. We simulate this process on a few
representative shells via ray-traces of perfect optics, perturbed
axially by low order Legendre polynomial terms. This elucidates some of
the requirements for the on-orbit measurements, and on possible
algorithms to perform the on-orbit adjustment with acceptably rapid
We report on the prospects for the study of the first stars, galaxies and black holes with the Generation-X Mission.
Generation-X is a NASA "Vision Mission" which completed preliminary study in lat e2006. Generation-X was approved
in February 2008 as an Astrophysics Strategic Mission Concept Study (ASMCS) and is baselined as an X-ray
observatory with 50 square meters of collecting area at 1 keV (500 times larger than Chandra) and 0.1 arcsecond angular
resolution (several times better than Chandra and 50 times better than the Constellation-X resolution goal). Such a high
energy observatory will be capable of detecting the earliest black holes and galaxies in the Universe, and will also study
the chemical evolution of the Universe and extremes of density, gravity, magnetic fields, and kinetic energy which
cannot be created in laboratories. A direct signature of the formation of the first galaxies, stars and black holes is
predicted to be X-ray emission at characteristic X-ray temperatures of 0.1-1 keV from the collapsing proto-galaxies
before they cool and form the first stars.
The calibration database implemented for the Chandra X-ray Observatory is the most detailed and extensive CalDB of
its kind to date. Built according to the NASA High Energy Astrophysics Science Archive Research Center (HEASARC)
CalDB prescription, the Chandra CalDB provides indexed, selectable calibration data for detector responses, mirror
effective areas, grating efficiencies, instrument geometries, default source aim points, CCD characteristics, and quantum
efficiencies, among many others. The combined index comprises approximately 500 entries. A standard FTOOLS
parametric interface allows users and tools to access the index. Unique dataset selection requires certain input
calibration parameters such as mission, instrument, detector, UTC date and time, and certain ranged parameter values.
The goals of the HEASARC CalDB design are (1) to separate software upgrades from calibration upgrades, (2) to allow
multi-mission use of analysis software (for missions with a compliant CalDB) and (3) to facilitate the use of multiple
software packages for the same data. While we have been able to meet the multivariate needs of Chandra with the
current CalDB implementation from HEASARC, certain requirements and desirable enhancements have been identified
that raise the prospect of a developmental rewrite of the CalDB system. The explicit goal is to meet Chandra's specific
needs better, but such upgrades may also provide significant advantages to CalDB planning for future missions. In
particular we believe we will introduce important features aiding in the development of mission-independent analysis
software. We report our current plans and progress.
The Chandra X-ray Observatory, which was launched in 1999, has to date completed almost seven years of successful
science and mission operations. The Observatory, which is the third of NASA's Great Observatories, is the most
sophisticated X-ray Observatory yet built. Chandra is designed to observe X-rays from high-energy regions of the
universe, such as the remnants of exploded stars, environs near black holes, and the hot tenuous gas filling the void
between the galaxies bound in clusters. The Chandra X-ray Center (CXC) is the focal point of scientific and mission
operations for the Observatory, and provides support to the scientific community in its use of Chandra. We describe the
CXC's organization, functions and principal processes, with emphasis on changes through different phases of the
mission from pre-launch to long-term operations, and we discuss lessons we have learned in developing and operating a
joint science and mission operations center.
X-rays provide one of the few bands through which we can study the epoch of reionization, when the first galaxies,
black holes and stars were born. To reach the sensitivity required to image these first discrete objects in the
universe needs a major advance in X-ray optics. Generation-X (Gen-X) is currently the only X-ray astronomy
mission concept that addresses this goal. Gen-X aims to improve substantially on the Chandra angular resolution
and to do so with substantially larger effective area. These two goals can only be met if a mirror technology
can be developed that yields high angular resolution at much lower mass/unit area than the Chandra optics,
matching that of Constellation-X (Con-X). We describe an approach to this goal based on active X-ray optics
that correct the mid-frequency departures from an ideal Wolter optic on-orbit. We concentrate on the problems
of sensing figure errors, calculating the corrections required, and applying those corrections. The time needed
to make this in-flight calibration is reasonable. A laboratory version of these optics has already been developed
by others and is successfully operating at synchrotron light sources. With only a moderate investment in these
optics the goals of Gen-X resolution can be realized.
The new frontier in astrophysics is the study of the very first stars, galaxies and black holes in the early Universe. These objects are beyond the grasp of the current generation of X-ray telescopes such as Chandra, and so the Generation-X Vision Mission has been proposed as an X-ray observatory which will be capable of detecting these earliest objects. Xray imaging and spectroscopy of such distant objects will require an X-ray telescope with large collecting area and high angular resolution. The Generation-X concept has 100 m2 collecting area at 1 keV (1000 times larger than Chandra) and 0.1 arcsecond angular resolution (several times better than Chandra and 50 times better than the resolution goal for Constellation-X). The baseline mission involves four 8 m diameter telescopes operating at Sun-Earth L2. Such large telescopes will require either robotic or human-assisted in-flight assembly. To achieve the required effective area with launchable mass, very lightweight grazing incidence X-ray optics must be developed, having an areal density 100 times lower than in Chandra, with perhaps 0.1 mm thick mirrors requiring on-orbit figure control. The suite of available detectors for Generation-X should include a large-area high resolution imager, a cryogenic imaging spectrometer and a grating spectrometer.
We describe the X-ray Data Acquisition and Control System (XDACS) used together with the X-ray Detection System (XDS) to characterize the X-ray image during testing of the AXAF P1/H1 mirror pair at the MSFC X-ray Calibration Facility. A variety of X-ray data were acquired, analyzed and archived during the testing including: mirror alignment, encircled energy, effective area, point spread function, system housekeeping and proportional counter window uniformity data. The system architecture is presented with emphasis placed on key features that include a layered UNIX tool approach, dedicated subsystem controllers, real-time X-window displays, flexibility in combining tools, network connectivity and system extensibility. The VETA test data archive is also described.
The 1-percent calibration accuracy goal of the Advanced X-ray Astrophysics Facility is being approached by way of an experiment at the National Synchrotron Light Source that will demonstrate the accuracy achievable in reflectance measurements conducted on coated flat mirrors in the 50 eV-12 keV energy range. The coatings will be of commercially produced Au, Ni, and Ir, deposited either by sputtering or by e-beam deposition. Optical constants will be estimated via the reflectance vs. angle-of-incidence method.
Advanced X-ray Astrophysics Facility (AXAF) X-ray optics testing is conducted by VETA-I, which consists of six nested Wolter type I grazing-incidence mirrors; VETA''s X-ray Detection System (VXDS) in turn measures the imaging properties of VETA-I, yielding FWHM and encircled energy of the X-ray image obtained, as well as its effective area. VXDS contains a high resolution microchannel plate imaging X-ray detector and a pinhole scanning system in front of proportional-counter detectors. VETA-I''s X-ray optics departs from the AXAF flight configuration in that it uses a temporary holding fixture; its mirror elements are not cut to final length, and are not coated with the metal film used to maximize high-energy reflection.