32 research outputs found
HRMA calibration handbook: EKC gravity compensated XRCF models
This document, consisting of hardcopy printout of explanatory text, figures, and tables, represents one incarnation of the AXAF high resolution mirror assembly (HRMA) Calibration Handbook. However, as we have envisioned it, the handbook also consists of electronic versions of this hardcopy printout (in the form of postscript files), the individual scripts which produced the various figures and the associated input data, the model raytrace files, and all scripts, parameter files, and input data necessary to generate the raytraces. These data are all available electronically as either ASCII or FITS files. The handbook is intended to be a living document and will be updated as new information and/or fabrication data on the HRMA are obtained, or when the need for additional results are indicated. The SAO Mission Support Team (MST) is developing a high fidelity HRMA model, consisting of analytical and numerical calculations, computer software, and databases of fundamental physical constants, laboratory measurements, configuration data, finite element models, AXAF assembly data, and so on. This model serves as the basis for the simulations presented in the handbook. The 'core' of the model is the raytrace package OSAC, which we have substantially modified and now refer to as SAOsac. One major structural modification to the software has been to utilize the UNIX binary pipe data transport mechanism for passing rays between program modules. This change has made it possible to simulate rays which are distributed randomly over the entrance aperture of the telescope. It has also resulted in a highly efficient system for tracing large numbers of rays. In one application to date (the analysis of VETA-I ring focus data) we have employed 2 x 10(exp 7) rays, a substantial improvement over the limit of 1 x 10(exp 4) rays in the original OSAC module. A second major modification is the manner in which SAOsac incorporates low spatial frequency surface errors into the geometric raytrace. The original OSAC included the ability to use Legendre-Fourier polynomials to describe deviations from the basic optical prescription. To this we have added bicubic splines to address a deficiency in the handling of the sharper deformations in the areas of mirror support pads. SAO has developed software (TRANS-FIT) to translate the most common finite element analysis models into these forms for incorporation into the raytrace program
Development of Ground-testable Phase Fresnel Lenses in Silicon
Diffractive/refractive optics, such as Phase Fresnel Lenses (PFL's), offer
the potential to achieve excellent imaging performance in the x-ray and
gamma-ray photon regimes. In principle, the angular resolution obtained with
these devices can be diffraction limited. Furthermore, improvements in signal
sensitivity can be achieved as virtually the entire flux incident on a lens can
be concentrated onto a small detector area. In order to verify experimentally
the imaging performance, we have fabricated PFL's in silicon using gray-scale
lithography to produce the required Fresnel profile. These devices are to be
evaluated in the recently constructed 600-meter x-ray interferometry testbed at
NASA/GSFC. Profile measurements of the Fresnel structures in fabricated PFL's
have been performed and have been used to obtain initial characterization of
the expected PFL imaging efficiencies.Comment: Presented at GammaWave05: "Focusing Telescopes in Nuclear
Astrophysics", Bonifacio, Corsica, September 2005, to be published in
Experimental Astronomy, 8 pages, 3 figure
A small X-ray corona of the narrow-angle tail radio galaxy NGC 1265 soaring through the Perseus cluster
A deep Chandra observation of NGC 1265 (3C 83.1B), the prototype for the
narrow-angled-tailed (NAT) radio galaxy, reveals a small cool X-ray thermal
corona (~ 0.6 keV) embedded in the hot ICM of the Perseus cluster (~ 6.7 keV).
The corona is asymmetric with a sharp edge (~ 2.2'', or 0.8 kpc from the
nucleus) to the south and an extension to the north (at least ~ 8'' from the
nucleus), which is interpreted as the action of ram pressure while solely the
static ICM confinement is unable to explain. We estimate that the corona is
moving with a velocity of ~ 2.4 - 4.2 times the local sound speed to the south.
The presence of the sharp edge for this small corona indicates that the
transport processes are largely suppressed by the magnetic field there. The
magnetic field around the corona also suppresses heat conduction by at least a
factor of ~ 60 across the corona boundary. We conclude that it is unrealistic
to study the interaction of the small X-ray coronae with the hot ICM without
the consideration of the roles that magnetic field plays, a factor not included
in current simulations. An absorbed (N_H=1.5-3x10^22 cm^-2) nucleus is also
detected, which is not usual for FR I radio galaxies. Weak X-ray emission from
three inner radio knots in the jets is also detected. Indentations at the east
and west of the corona indicate interaction between the jets and the X-ray
corona. Narrow jets carry great amounts of energy out of the central AGN and
release the energy outside the corona, preserving the tiny and vulnerable
corona. This case reveals that the inner kpc core of the corona of massive
galaxies can survive both high-speed stripping and powerful AGN feedback. Thus,
the cooling of the X-ray coronae potentially provides fuel to the central SMBH
in rich environments where the amount of the galactic cold gas is at a minimum.Comment: revised version, 11 pages, 4 figures, emulateapj5.sty, accepted by
ApJ, for the version with high-resolution figures
(http://hea-www.harvard.edu/~msun/n1265.ps
High-resolution x-ray telescopes
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
(stellar-mass 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.Comment: 19 pages, 11 figures, SPIE Conference 7803 "Adaptive X-ray Optics",
part of SPIE Optics+Photonics 2010, San Diego CA, 2010 August 2-
The X-ray luminous cluster underlying the z = 1.04 quasar PKS1229-021
We present a 100 ks Chandra observation studying the extended X-ray emission
around the powerful z=1.04 quasar PKS1229-021. The diffuse cluster X-ray
emission can be traced out to ~15 arcsec (~120 kpc) radius and there is a drop
in the calculated hardness ratio inside the central 5 arcsec consistent with
the presence of a cool core. Radio observations of the quasar show a strong
core and a bright, one-sided jet leading to the SW hot spot and a second hot
spot visible on the counter-jet side. Although the wings of the quasar PSF
provided a significant contribution to the total X-ray flux at all radii where
the extended cluster emission was detected, we were able to accurately subtract
off the PSF emission using ChaRT and marx simulations. The resulting steep
cluster surface brightness profile for PKS1229-021 appears similar to the
profile for the FRII radio galaxy 3C444, which has a similarly rapid surface
brightness drop caused by a powerful shock surrounding the radio lobes (Croston
et al.). Using a model surface brightness profile based on 3C444, we estimated
the total cluster luminosity for PKS1229-021 to be L_X ~ 2 x 10^{44} erg/s. We
discuss the difficulty of detecting cool core clusters, which host bright X-ray
sources, in high redshift surveys.Comment: 10 pages, 9 figures, accepted by MNRA
The X-ray luminous cluster underlying the bright radio-quiet quasar H1821+643
We present a Chandra observation of the only low redshift, z=0.299, galaxy
cluster to contain a highly luminous radio-quiet quasar, H1821+643. By
simulating the quasar PSF, we subtract the quasar contribution from the cluster
core and determine the physical properties of the cluster gas down to 3 arcsec
(15 kpc) from the point source. The temperature of the cluster gas decreases
from 9.0\pm0.5 keV down to 1.3\pm0.2 keV in the centre, with a short central
radiative cooling time of 1.0\pm0.1 Gyr, typical of a strong cool-core cluster.
The X-ray morphology in the central 100 kpc shows extended spurs of emission
from the core, a small radio cavity and a weak shock or cold front forming a
semi-circular edge at 15 arcsec radius. The quasar bolometric luminosity was
estimated to be 2 x 10^{47} erg per sec, requiring a mass accretion rate of 40
Msolar per yr, which corresponds to half the Eddington accretion rate. We
explore possible accretion mechanisms for this object and determine that Bondi
accretion, when boosted by Compton cooling of the accretion material, could
provide a significant source of the fuel for this outburst. We consider
H1821+643 in the context of a unified AGN accretion model and, by comparing
H1821+643 with a sample of galaxy clusters, we show that the quasar has not
significantly affected the large-scale cluster gas properties.Comment: 20 pages, 19 figures, accepted by MNRA
UBVRI Light Curves of 44 Type Ia Supernovae
We present UBVRI photometry of 44 type-Ia supernovae (SN Ia) observed from
1997 to 2001 as part of a continuing monitoring campaign at the Fred Lawrence
Whipple Observatory of the Harvard-Smithsonian Center for Astrophysics. The
data set comprises 2190 observations and is the largest homogeneously observed
and reduced sample of SN Ia to date, nearly doubling the number of
well-observed, nearby SN Ia with published multicolor CCD light curves. The
large sample of U-band photometry is a unique addition, with important
connections to SN Ia observed at high redshift. The decline rate of SN Ia
U-band light curves correlates well with the decline rate in other bands, as
does the U-B color at maximum light. However, the U-band peak magnitudes show
an increased dispersion relative to other bands even after accounting for
extinction and decline rate, amounting to an additional ~40% intrinsic scatter
compared to B-band.Comment: 84 authors, 71 pages, 51 tables, 10 figures. Accepted for publication
in the Astronomical Journal. Version with high-res figures and electronic
data at http://astron.berkeley.edu/~saurabh/cfa2snIa
Iliofemoral Venous Thrombosis Caused by Compression of an Internal Iliac Artery Aneurysm: A Minimally Invasive Treatment
Purpose: To report the success of a minimally invasive treatment for phlegmasia cerulea dolens without gangrene caused by compression from an internal iliac artery aneurysm. Methods and Results: An 81-year-old male with a 1-month history of paralysis owing to a hemorrhagic stroke presented with massive edema and skin mottling of the right lower extremity. Imaging confirmed right iliofemoral deep vein thrombosis caused by compression from a 4-cm internal iliac artery aneurysm. With thrombolysis ruled out, a minimally invasive treatment plan was undertaken, featuring percutaneous coil embolization of the aneurysm and surgical venous thrombectomy with proximal arteriovenous fistula creation and iliac vein stent placement. Failure of the coils to embolize the iliac aneurysm prompted the use of an endovascular graft to exclude the aneurysm. The patient\u27s symptoms subsided, and he has a patent right iliofemoral venous system and internal iliac artery at his latest (16-month) follow-up. Conclusions: This case demonstrates that minimally invasive endovascular and open techniques can be combined to achieve an optimum outcome in patients at high risk for standard surgical approaches
Iliofemoral Venous Thrombosis Caused by Compression of an Internal Iliac Artery Aneurysm: A Minimally Invasive Treatment
Purpose: To report the success of a minimally invasive treatment for phlegmasia cerulea dolens without gangrene caused by compression from an internal iliac artery aneurysm.
Methods and Results: An 81-year-old male with a 1-month history of paralysis owing to a hemorrhagic stroke presented with massive edema and skin mottling of the right lower extremity. Imaging confirmed right iliofemoral deep vein thrombosis caused by compression from a 4-cm internal iliac artery aneurysm. With thrombolysis ruled out, a minimally invasive treatment plan was undertaken, featuring percutaneous coil embolization of the aneurysm and surgical venous thrombectomy with proximal arteriovenous fistula creation and iliac vein stent placement. Failure of the coils to embolize the iliac aneurysm prompted the use of an endovascular graft to exclude the aneurysm. The patient\u27s symptoms subsided, and he has a patent right iliofemoral venous system and internal iliac artery at his latest (16-month) follow-up.
Conclusions: This case demonstrates that minimally invasive endovascular and open techniques can be combined to achieve an optimum outcome in patients at high risk for standard surgical approaches
Diagnosis of Aortocaval Fistula by Computed Tomography
A case of an aortocaval fistula documented by contrast-enhancement computed tomography is reported. In the presence of a large abdominal aortic aneurysm, the computed tomography (CT) triad findings of: (1) vena caval effacement, (2) loss of the fat plane between the aorta and vena cava, and (3) rapid flow of contrast from the aorta into a dilated inferior vena cava is characteristic of an aortocaval fistula