38 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
Finding Gravitational Lenses With X-rays
There are , 0.1 and 0.01 gravitationally lensed X-ray sources per
square degree with soft X-ray fluxes exceeding and
respectively. These sources will be detected
serendipitously with the Chandra X-ray Observatory at a rate of 1--3 lenses per
year of high resolution imaging. The low detection rate is due to the small
area over which the HRC and ACIS cameras have the <1\farcs5 FWHM resolution
necessary to find gravitational lenses produced by galaxies. Deep images of
rich clusters at intermediate redshifts should yield one wide separation
(\Delta\theta \gtorder 5\farcs0) multiply-imaged background X-ray source for
every , 30 and 300 clusters imaged to the same flux limits.Comment: 13 pages, including 5 figures, submitted to ApJ Letter
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
Bow shock and radio halo in the merging cluster A520
Chandra observations of the merging galaxy cluster A520 reveal a prominent
bow shock with M=2.1+0.4-0.3. This is only the second clear example of a
substantially supersonic merger shock front in clusters. Comparison of the
X-ray image with that of the previously known radio halo reveals a coincidence
of the leading edge of the halo with the bow shock, offering an interesting
experimental setup for determining the role of shocks in the radio halo
generation. The halo in A520 apparently consists of two spatially distinct
parts, the main turbulence-driven component and a cap-like forward structure
related to the shock, where the latter may provide pre-energized electrons for
subsequent turbulent re-acceleration. The radio edge may be caused by electron
acceleration by the shock. If so, the synchrotron spectrum should have a slope
of 1.2 right behind the edge with quick steepening further away from the edge.
Alternatively, if shocks are inefficient accelerators, the radio edge may be
explained by an increase in the magnetic field and density of pre-existing
relativistic electrons due to gas compression. In the latter model, there
should be radio emission in front of the shock with the same spectrum as that
behind it, but 10-20 times fainter. If future sensitive radio measurements do
not find such pre-shock emission, then the electrons are indeed accelerated (or
re-accelerated) by the shock, and one will be able to determine its
acceleration efficiency. We also propose a method to estimate the magnetic
field strength behind the shock, based on measuring the dependence of the radio
spectral slope upon the distance from the shock. In addition, the radio edge
provides a way to constrain the diffusion speed of the relativistic electrons.Comment: 6 pages (emulateapj style), color figures. Minor text clarifications,
improved figure. ApJ in pres
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-
AEGIS-X: The Chandra Deep Survey of the Extended Groth Strip
We present the AEGIS-X survey, a series of deep Chandra ACIS-I observations
of the Extended Groth Strip. The survey comprises pointings at 8 separate
positions, each with nominal exposure 200ks, covering a total area of
approximately 0.67 deg2 in a strip of length 2 degrees. We describe in detail
an updated version of our data reduction and point source detection algorithms
used to analyze these data. A total of 1325 band-merged sources have been found
to a Poisson probability limit of 4e-6, with limiting fluxes of 5.3e-17
erg/cm2/s in the soft (0.5-2 keV) band and 3.8e-16 erg/cm2/s in the hard (2-10
keV) band. We present simulations verifying the validity of our source
detection procedure and showing a very small, <1.5%, contamination rate from
spurious sources. Optical/NIR counterparts have been identified from the DEEP2,
CFHTLS, and Spitzer/IRAC surveys of the same region. Using a likelihood ratio
method, we find optical counterparts for 76% of our sources, complete to
R(AB)=24.1, and, of the 66% of the sources that have IRAC coverage, 94% have a
counterpart to a limit of 0.9 microJy at 3.6 microns (m(AB)=23.8). After
accounting for (small) positional offsets in the 8 Chandra fields, the
astrometric accuracy of the Chandra positions is found to be 0.8 arcsec RMS,
however this number depends both on the off-axis angle and the number of
detected counts for a given source. All the data products described in this
paper are made available via a public website.Comment: 17 pages, 9 figures. Accepted for publication in ApJS. Data products
are available at http://astro.imperial.ac.uk/research/aegis
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
Optics Requirements For The Generation-X X-Ray Telescope
US, European, and Japanese space agencies each now operate successful X-ray missions -- NASA s Chandra, ESA s XMM-Newton, and JAXA s Suzaku observatories. Recently these agencies began a collaboration to develop the next major X-ray astrophysics facility -- the International X-ray Observatory (IXO) -- for launch around 2020. IXO will provide an order-of-magnitude increase in effective area, while maintaining good (but not sub-arcsecond) angular resolution. X-ray astronomy beyond IXO will require optics with even larger aperture areas and much better angular resolution. We are currently conducting a NASA strategic mission concept study to identify technology issues and to formulate a technology roadmap for a mission -- Generation-X (Gen-X) -- to provide these capabilities. Achieving large X-ray collecting areas in a space observatory requires extremely lightweight mirrors
UBVRI Light curves of 44 Type Ia supernovae
We present UBVRI photometry of 44 Type la supernovae (SNe la) 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 SNe la to date, nearly doubling the number of well-observed, nearby SNe la with published multicolor CCD light curves. The large sample of [U-band photometry is a unique addition, with important connections to SNe la observed at high redshift. The decline rate of SN la 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 âŒ40% intrinsic scatter compared to the B band