F. Scott Porter

Suzaku Observations of Abell 1795: Cluster Emission to r200

We report Suzaku observations of the galaxy cluster Abell 1795 that extend to r200 �2 Mpc, the radius within which the mean cluster mass density is 200 times the cosmic critical density. These observations are the first to probe the state of the intracluster medium in this object at r > 1.3 Mpc. We sample two disjoint sectors in the cluster outskirts (1.3 0.4 Mpc and find that it falls relatively rapidly (Tdeprojected / r −0.9 ), reaching a value about one third of its peak at the largest radius we can measure it. Assuming the intracluster medium is in hydrostatic equilibrium and is polytropic, we find a polytropic index of =1 .3 +0.3 −0.2 and we estimate a mass of 4.1 +0.5 −0.3 ×10 14 M⊙ within 1.3 Mpc, somewhat (2.7 σ) lower than that reported by previous observers. However, our observations provide evidence for departure from hydrostatic equilibrium at radii as small as

Suzaku Observations of the Local and Distant Hot ISM

Suzaku observed the molecular cloud MBM 12 and a blank field less than 3 ◦ away to separate the local and distant components of the diffuse soft X-ray background. Towards MBM 12, a local (D 275pc) O VII emission line was clearly detected with an intensity of 3.5 photons cm −2 s −1 sr −1 (or line units, LU), and the O VIII flux was < 0.34 LU. The origin of this O VII emission could be hot gas in the Local Hot Bubble (LHB), charge exchange within the heliosphere with oxygen ions from the solar wind (SWCX), or both. If entirely from the LHB, the emission could be explained by a region with emission measure of 0.0075cm −6 pc and a temperature of 1.2 ×10 6 K. However, this temperature and emission measure implies 1/4 keV emission in excess of observations. There is no evidence in the X-ray light curve or solar wind data for a significant contribution from geocoronal SWCX, although interplanetary SWCX is still possible. In any case, the observed O VII flux represents an upper limit to both the LHB emission and interplanetary SWCX in this direction. The blank field was observed immediately afterwards. The net off-cloud O VII and O VIII intensities were (respectively) 2.34 ±0.33 and 0.77 ±0.16 LU, after subtracting the on-cloud foreground emission. If this more distant O VII and O VIII emission is from a thermal plasma in collisional equilibrium beyond the Galactic disk, we infer it has a temperature of (2.1 ±0.1) ×10 6 K with an emission measure of (4 ±0.6) ×10 −3 cm −6 pc.

The Astro-H High Resolution Soft X-Ray Spectrometer

We present the overall design and performance of the Astro-H (Hitomi) Soft X-Ray Spectrometer (SXS). The instrument uses a 36-pixel array of x-ray microcalorimeters at the focus of a grazing-incidence x-ray mirror Soft X-Ray Telescope (SXT) for high-resolution spectroscopy of celestial x-ray sources. The instrument was designed to achieve an energy resolution better than 7 eV over the 0.3-12 keV energy range and operate for more than 3 years in orbit. The actual energy resolution of the instrument is 4-5 eV as demonstrated during extensive ground testing prior to launch and in orbit. The measured mass flow rate of the liquid helium cryogen and initial fill level at launch predict a lifetime of more than 4 years assuming steady mechanical cooler performance. Cryogen-free operation was successfully demonstrated prior to launch. The successful operation of the SXS in orbit, including the first observations of the velocity structure of the Perseus cluster of galaxies, demonstrates the viability and power of this technology as a tool for astrophysics.

Soft x-ray spectrometer (SXS): The high-resolution cryogenic spectrometer onboard ASTRO-H

We present the development status of the Soft X-ray Spectrometer (SXS) onboard the ASTRO-H mission. The SXS provides the capability of high energy-resolution X-ray spectroscopy of a FWHM energy resolution of < 7eV in the energy range of 0.3 – 10 keV. It utilizes an X-ray micorcalorimeter array operated at 50 mK. The SXS microcalorimeter subsystem is being developed in an EM-FM approach. The EM SXS cryostat was developed and fully tested and, although the design was generally confirmed, several anomalies and problems were found. Among them is the interference of the detector with the micro-vibrations from the mechanical coolers, which is the most difficult one to solve. We have pursued three different countermeasures and two of them seem to be effective. So far we have obtained energy resolutions satisfying the requirement with the FM cryostat.

Suzaku Observations of the North Polar Spur: Evidence for Nitrogen Enhancement

We present observations of the North Polar Spur (NPS) using the X-ray Imaging Spectrometer (XIS) aboard the Suzaku X-ray satellite. The NPS is a large region of enhanced soft X-ray and radio emission projected above the plane of the Galaxy, likely produced by a series of supernovae and stellar winds from the nearby Sco–Cen OB association. The exceptional sensitivity and spectral resolution of the XIS below 1 keV allow unprecedented probing of low-energy spectral lines, including C VI (0.37 keV) and N VII (0.50 keV), and we have detected highly-ionized nitrogen toward the NPS for the first time. For this single pointing toward the brightest 3/4 keV emission (l = 26: 8, b =+ 22: 0), the best-fit NPS emission model implies a hot (kT � 0:3 keV), collisional ionization equilibrium (CIE) plasma with depleted C, O, Ne, Mg, and Fe abundances of less than 0.5 solar, but an enhanced N abundance, with N=O = .4:0 +0:4 � 0:5 / times solar. The temperature and total thermal energy of the gas suggest heating by one or more supernovae, while the enhanced nitrogen abundance is best explained by enrichment from stellar material that has been processed by the CNO cycle. Due to the time required to develop AGB stars, we conclude that this N=O enhancement cannot be caused by the Sco–Cen OB association, but may result from a previous enrichment episode in the solar neighborhood.

The design, implementation, and performance of the Atro-H SXS calorimeter array and anti-coincidence detector

The calorimeter array of the JAXA Astro-H (renamed Hitomi) Soft X-ray Spectrometer (SXS) was designed to provide unprecedented spectral resolution of spatially extended cosmic x-ray sources and of all cosmic x-ray sources in the Fe-K band around 6 keV, enabling essential plasma diagnostics. The SXS has a square array of 36 microcalorimeters at the focal plane. These calorimeters consist of ion-implanted silicon thermistors and HgTe thermalizing x-ray absorbers. These devices have demonstrated a resolution of better than 4.5 eV at 6 keV when operated at a heat-sink temperature of 50 mK. We will discuss the basic physical parameters of this array, including the array layout, thermal conductance of the link to the heat sink, resistance function, absorber details, and means of attaching the absorber to the thermistorbearing element. We will also present the thermal characterization of the whole array, including thermal conductance and crosstalk measurements and the results of pulsing the frame temperature via alpha particles, heat pulses, and the environmental background. A silicon ionization detector is located behind the calorimeter array and serves to reject events due to cosmic rays. We will briefly describe this anti-coincidence detector and its performance.

On Lunar Exospheric Column Densities and Solar Wind Access Beyond the Terminator from ROSAT Soft X-Ray Observations of Solar Wind Charge Exchange

We analyze the Rontgen satellite (ROSAT) position sensitive proportional counter soft X-ray image of the Moon taken on 29 June 1990 by examining the radial profile of the surface brightness in three wedges: two 19 ◦ wedges (one north and one south) 13-32 ◦ off the terminator toward the dark side and one wedge 38 ◦ wide centered on the antisolar direction. The radial profiles of both the north and the south wedges show significant limb brightening that is absent in the 38 ◦ wide antisolar wedge. An analysis of the soft X-ray intensity increase associated with the limb brightening shows that its magnitude is consistent with that expected due to solar wind charge exchange (SWCX) with the tenuous lunar atmosphere based on lunar exospheric models and hybrid simulation results of solar wind access beyond the terminator. Soft X-ray imaging thus can independently infer the total lunar limb column density including all species, a property that before now has not been measured, and provide a large-scale picture of the solar wind-lunar interaction. Because the SWCX signal appears to be dominated by exospheric species arising from solar wind implantation, this technique can also determine how the exosphere varies with solar wind conditions. Now, along with Mars, Venus, and Earth, the Moon represents another solar system body at which SWCX has been observed.

The x-ray microcalorimeter on the NeXT mission

The Soft X-ray Spectrometer (SXS) onboard the NeXT (New exploration X-ray Telescope) is an X-ray spectrometer utilizing an X-ray microcalorimeter array. Combined with the soft X-ray telescope of 6 m focal length, the instrument will have a ~ 290cm2 effective at 6.7 keV. With the large effective area and the energy resolution as good as 6 eV (FWHM), the instrument is very suited for the high-resolution spectroscopy of iron K emission line. One of the major scientific objectives of SXS is to determine turbulent and/or macroscopic motions of the hot gas in clusters of galaxies of up to z ~ 1. The instruments will use 6 × 6 or 8 × 8 format microcalorimeter array which is similar to that of Suzaku XRS. The detector will be cooled to a cryogenic temperature of 50 mK by multi-stage cooling system consisting of adiabatic demagnetization refrigerator, super fluid He, a 3He Joule Thomson cooler, and double-stage stirling cycle cooler.

Multiplexed readout of uniform arrays of TES x-ray microcalorimeters suitable for Constellation-X

Following our development of a superconducting transition-edge-sensor (TES) microcalorimeter design that en- ables reproducible, high performance (routinely better than 3 eV FWHM energy resolution at 6 keV) and is compatible with high-fill-factor arrays, we have directed our efforts towards demonstrating arrays of identical pixels using the multiplexed read-out concept needed for instrumenting the Constellation-X X-ray Microcalorime- ter Spectrometer (XMS) focal plane array. We have used a state-of-the-art, time-division SQUID multiplexer system to demonstrate 2 ×8 multiplexing (16 pixels read out with two signal channels) with an acceptably modest level of degradation in the energy resolution. The average resolution for the 16 multiplexed pixels was 2.9 eV, and the distribution of resolution values had a relative standard deviation of 5%. The performance of the array while multiplexed is well understood. The technical path to realizing multiplexing for the XMS instrument on the scale of 32 pixels per signal channel includes increasing the system bandwidth by a factor of four and reducing the non-multiplexed SQUID noise by a factor of two. In this paper we discuss the characteristics of a uniform 8 ×8 array and its performance when read out non- multiplexed and with various degrees of multiplexing. We present data acquired through the readout chain from the multiplexer electronics, through the real-time demultiplexer software, to storage for later signal processing. We also report on a demonstration of real-time data processing. Finally, because the multiplexer provides unprecedented simultaneous access to the pixels of the array, we were able to measure the array-scale uniformity of TES calorimeter parameters such as the individual thermal conductances and superconducting transition temperatures of the pixels. Detector uniformity is essential for optimal operation of a multiplexed array, and we found that the distributions of thermal conductances, transition temperatures, and transition slopes were sufficiently tight to avoid significant compromises in the operation of any pixel.

Performance of the helium dewar and cryocoolers of ASTRO-H SXS

The Soft X-ray Spectrometer (SXS) is a cryogenic high-resolution X-ray spectrometer onboard the ASTRO-H satellite, that achieves energy resolution better than 7 eV at 6 keV, by operating the detector array at 50 mK using an adiabatic demagnetization refrigerator. The cooling chain from room temperature to the ADR heat sink is composed of 2-stage Stirling cryocoolers, a 4He Joule-Thomson cryocooler, and super uid liquid He, and is installed in a dewar. It is designed to achieve a helium lifetime of more than 3 years with a minimum of 30 liters. The satellite was launched on 2016 February 17, and the SXS worked perfectly in orbit, until March 26 when the satellite lost its function. It was demonstrated that the heat load on the He tank was about 0.7 mW, which would have satisfied the lifetime requirement. This paper describes the design, results of ground performance tests, prelaunch operations, and initial operation and performance in orbit of the flight dewar and cryocoolers.