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 Mpc < r < 1.9 Mpc) and detect X-ray emission in only one of them to a limiting (3 ) soft X-ray surface brightness of B0:5–2keV = 1.8 10 12 erg s 1 cm 2 deg , a level less than 20% of the cosmic X-ray background brightness. We trace the run of temperature with radius at r > 0.4 Mpc and find that it falls relatively rapidly (Tdeprojected / r ), 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 Γ = 1.3 0:2 and we estimate a mass of (4.1 +0:5 0:3) 10Mˇ within 1.3 Mpc, somewhat (2.7 ) lower than that reported by previous observers. However, our observations provide evidence for departure from hydrostatic equilibrium at radii as small as r 1.3 Mpc r500 in this apparently regular and symmetrical cluster.

Multimode bolometer development for the PIXIE instrument

The Primordial Inflation Explorer (PIXIE) is an Explorer-class mission concept designed to measure the polar- ization and absolute intensity of the cosmic microwave background. In the following, we report on the design, fabrication, and performance of the multimode polarization-sensitive bolometers for PIXIE, which are based on silicon thermistors. In particular we focus on several recent advances in the detector design, including the implementation of a scheme to greatly raise the frequencies of the internal vibrational modes of the large-area, low-mass optical absorber structure consisting of a grid of micromachined, ion-implanted silicon wires. With ∼ 30 times the absorbing area of the spider-web bolometers used by Planck, the tensioning scheme enables the PIXIE bolometers to be robust in the vibrational and acoustic environment at launch of the space mission. More generally, it could be used to reduce microphonic sensitivity in other types of low temperature detectors. We also report on the performance of the PIXIE bolometers in a dark cryogenic environment.

Position-sensitive microcalorimeters for large-field high-energy resolution astrophysics

We are developing a distributed-readout imaging spectrometer named Position-Sensitive Transition-Edge Sensor (PoST). A PoST is a microcalorimeter capagble of 1D imaging spectroscopy. It consists of two Transition-Edge Sensors (TESs) at each end of a long x-ray absorber. The position of an x-ray absorption event in the PoST is determined from the rise time and relative signal sizes in the two sensors. The energy of the absorbed photon is inferred from the sum of the two pulses. We discuss the modeling, operation, and readout of PoSTs and their application to the Constellation-X mission.

High Resolution Spectroscopy of the X‐Ray Emission of GRBs by IMBOSS on the ISS

The IMBOSS (Interstellar/Intergalactic Medium and gamma‐ray Burst Observatory and Spectroscopy Survey) is an experiment proposed to fly on the ISS (International Space Station), in order to perform an all‐sky survey to study the diffuse X‐ray emission and to measure the spectra of Gamma‐Ray Bursts (GRB) with high energy resolution in the 0.1–10 keV energy range. In a 3‐year mission, the experiment will detect about 20 to 40 GRBs. In several events, we can perform high resolution spectroscopy of the iron emission lines and absorption edges. Such components have been observed by BeppoSAX and Chandra. The measurements of these features would provide a direct diagnostic of the physical and kinematical state of the medium surrounding a GRB. Furthermore, they would supply information about the origin of the progenitors of the GRBs (probably a supernova explosion of massive stars) and their site formation (possibly a star‐forming region).