2,773 research outputs found
The Formal Underpinnings of the Response Functions used in X-Ray Spectral Analysis
This work provides an in-depth mathematical description of the response
functions that are used for spatial and spectral analysis of X-ray data. The
use of such functions is well-known to anyone familiar with the analysis of
X-ray data where they may be identified with the quantities contained in the
Ancillary Response File (ARF), the Redistribution Matrix File (RMF), and the
Exposure Map. Starting from first-principles, explicit mathematical expressions
for these functions, for both imaging and dispersive modes, are arrived at in
terms of the underlying instrumental characteristics of the telescope including
the effects of pointing motion. The response functions are presented in the
context of integral equations relating the expected detector count rate to the
source spectrum incident upon the telescope. Their application to the analysis
of several source distributions is considered. These include multiple, possibly
overlapping, and spectrally distinct point sources, as well as extended
sources. Assumptions and limitations behind the usage of these functions, as
well as their practical computation are addressed.Comment: 22 pages, 3 figures (LaTeX
TGCat, The Chandra Transmission Grating Catalog and Archive: Systems, Desgin and Accessibility
The recently released Chandra Transmission Grating Catalog and Archive, TGCat, presents a fully dynamic on-line catalog allowing users to browse and categorize Chandra gratings observations quickly and easily, generate custom plots of resulting response corrected spectra on-line without the need for special software and to download analysis ready products from multiple observations in one convenient operation. TGCat has been registered as a VO resource with the NVO providing direct access to the catalogs interface. The catalog is supported by a back-end designed to automatically fetch newly public data, process, archive and catalog them, At the same time utilizing an advanced queue system integrated into the archive's MySQL database allowing large processing projects to take advantage of an unlimited number of CPUs across a network for rapid completion. A unique feature of the catalog is that all of the high level functions used to retrieve inputs from the Chandra archive and to generate the final data products are available to the user in an ISIS written library with detailed documentation. Here we present a structural overview of the Systems, Design, and Accessibility features of the catalog and archive.United States. National Aeronautics and Space Administration (Chandra X-ray Center (CXC) NASA contract NAS8-03060)United States. National Aeronautics and Space Administration (Smithsonian Astrophysical Observatory (SAO) contract SV3-73016 for the Chandra X-Ray Center and Science Instruments
The Chandra X-ray Observatory: An Astronomical Facility Available to the World
The Chandra X-ray observatory, one of NASA's "Great Observatories," provides high angular and spectral resolution X-ray data which is freely available to all. In this review I describe the instruments on chandra along with their current calibration, as well as the chandra proposal system, the freely-available Chandra analysis software package CIAO, and the Chandra archive. As Chandra is in its 6th year of operation, the archive already contains calibrated observations of a large range of X-ray sources. The Chandra X-ray Center is committed to assisting astronomers from any country who wish to use data from the archive or propose for observation
REFINED ORBITAL SOLUTION AND QUIESCENT VARIABILITY IN THE BLACK HOLE TRANSIENT GS 1354-64 (= BW Cir)
In Casares et al. we presented the first radial velocity curve of the companion star to BW Cir which demonstrates the presence of a black hole in this historical X-ray transient. But these data were affected by aliasing and two possible periods at 2.5445 days and 2.5635 days were equally possible. Here we present new spectroscopic data that enable us to break the 1-year aliasing and confirm 2.5445 days as the correct orbital period. We also present R-band photometry over 14 years, which reveals the presence of important flaring activity dominating the light curves.Spain. Ministerio de Ciencia y Tecnología (Spanish MCYT grant AYA2002-0036)Spain. Ministerio de Ciencia y Tecnología (programme Ramon y Cajal)Chandra X-ray Center (U.S.) (NASA Contract NAS8-03060
The X-ray R Aquarii: A Two-sided Jet and Central Source
We report Chandra ACIS-S3 x-ray imaging and spectroscopy of the R Aquarii
binary system that show a spatially resolved two-sided jet and an unresolved
central source. This is the first published report of such an x-ray jet seen in
an evolved stellar system comprised of ~2-3 solar masses. At E < 1 keV, the
x-ray jet extends both to the northeast and southwest relative to the central
binary system. At 1 < E < 7.1 keV, R Aqr is a point-like source centered on the
star system. While both 3.5-cm radio continuum emission and x-ray emission
appear coincident in projection and have maximum intensities at ~7.5" northeast
of the central binary system, the next strongest x-ray component is located
\~30" southwest of the central binary system and has no radio continuum
counterpart. The x-ray jets are likely shock heated in the recent past, and are
not in thermal equilibrium. The strongest southwest x-ray jet component may
have been shocked recently since there is no relic radio emission as expected
from an older shock. At the position of the central binary, we detect x-ray
emission below 1.6 keV consistent with blackbody emission at T ~2 x 10^6 K. At
the central star there is also a prominent 6.4 keV feature, a possible
fluorescence or collisionally excited Fe K-alpha line from an accretion disk or
from the wind of the giant star. For this excitation to occur, there must be an
unseen hard source of x-rays or particles in the immediate vicinity of the hot
star. Such a source would be hidden from view by the surrounding edge-on
accretion disk.Comment: PS, 20 pages, including 3 figures PNG, JPG - accepted for publication
in ApJ Letters. Subject headings: stars: individual (R Aquarii) -- binaries:
symbiotic -- circumstellar matter -- stars: white dwarfs -- stars: winds,
outflows -- radio continuum: stars -- x-rays: genera
The MYStIX wide-field near-infrared data: Optimal photometry in crowded fields
We present JHK infrared data from the UK InfraRed Telescope (UKIRT) for a subset of the regions of the Massive Young Star-Forming Complex Study in Infrared and X-ray (MYStIX) survey. Some of the data were obtained specifically for the MYStIX project, and some as part of the UKIRT Infrared Deep Sky Survey's Galactic Plane Survey. In most of these fields, crowding is a significant issue for aperture photometry, and so we have re-extracted the photometry from the processed images using an optimal extraction technique, and we describe how we adapt the optimal technique to mitigate the effects of crowding. © 2013. The American Astronomical Society. All rights reserved.The MYStIX project is supported at Penn State by NASA grant NNX09AC74G, NSF grant AST-0908038, and the Chandra ACIS Team contract SV4-74018 (G. Garmire & L. Townsley, Principal Investigators), issued by the Chandra X-ray Center, which is operated by the Smithsonian Astrophysical Observatory for and on behalf of NASA under contract NAS8-03060. This research made use of data products from the Chandra Data Archive
Questioning a 3.5 keV dark matter emission line
Context. Recent findings of line emission at 3.5 keV in both individual and
stacked X-ray spectra of galaxy clusters have been speculated to have dark
matter origin. Aims. If the origin is indeed dark matter, the emission line is
expected to be detectable from the Milky Way dark matter halo. Methods. We
perform a line search in public Chandra X-ray observations of the region near
Sgr A*. We derive upper limits on the line emission flux for the 2.0-9.0 keV
energy interval and discuss their potential physical interpretations including
various scenarios of decaying and annihilating dark matter. Results. While find
no clear evidence for its presence, the upper flux limits are not inconsistent
with the recent detections for conservative mass profiles of the Milky Way.
Conclusions. The results depends mildly on the spectral modelling and strongly
on the choice of dark matter profile.Comment: 10 pages, 7 figures, matches version accepted by A&
Chandra astrometry sets a tight upper limit to the proper motion of SGR 1900+14
The soft gamma-ray repeater (SGR) SGR 1900+14 lies a few arcminutes outside
the edge of the shell supernova remnant (SNR) G42.8+0.6. A physical association
between the two systems has been proposed - for this and other SGR-SNR pairs -
based on the expectation of high space velocities for SGRs in the framework of
the magnetar model. The large angular separation between the SGR and the SNR
center, coupled with the young age of the system, suggest a test of the
association with a proper motion measurement. We used a set of three
Chandra/ACIS observations of the field spanning 5 years to perform accurate
relative astrometry in order to measure the possible angular displacement of
the SGR as a function of time. Our investigation sets a 3-sigma upper limit of
70 mas/yr to the overall proper motion of the SGR. Such a value argues against
an association of SGR 1900+14 with G42.8+0.6 and adds further support to the
mounting evidence for an origin of the SGR within a nearby, compact cluster of
massive stars.Comment: Accepted for publication in The Astrophysical Journal. 4 pages in
emulate-apj styl
The Extraordinary X-ray Light Curve of the Classical Nova V1494 Aquilae (1999 #2) in Outburst: The Discovery of Pulsations and a "Burst"
V1494 Aql (Nova Aql 1999 No. 2) was discovered on 2 December 1999. We
obtained Chandra ACIS-I spectra on 15 April and 7 June 2000 which appear to
show only emission lines. Our third observation, on 6 August, showed that its
spectrum had evolved to that characteristic of a Super Soft X-ray Source. We
then obtained Chandra LETG+HRC-S spectra on 28 September (8 ksec) and 1 October
(17 ksec). We analyzed the X-ray light curve of our grating observations and
found both a short time scale ``burst'' and oscillations. Neither of these
phenomena have previously been seen in the light curve of a nova in outburst.
The ``burst'' was a factor of 10 rise in X-ray counts near the middle of the
second observation, and which lasted about 1000 sec; it exhibited at least two
peaks, in addition to other structure. Our time series analysis of the combined
25 ksec observation shows a peak at 2500 s which is present in independent
analyses of both the zeroth order image and the dispersed spectrum and is not
present in similar analyses of grating data for HZ 43 and Sirius B. Further
analyses of the V1494 Aql data find other periods present which implies that we
are observing non-radial g+ modes from the pulsating, rekindled white dwarf.Comment: ApJ accepte
The Complicated Evolution of the ACIS Contamination Layer over the Mission Life of the Chandra X-ray Observatory
The Chandra X-ray Observatory was launched almost 19 years ago and has been
delivering spectacular science over the course of its mission. The Advanced CCD
Imager Spectrometer is the prime instrument on the satellite, conducting over
90% of the observations. The CCDs operate at a temperature of -120 C and the
optical blocking filter in front of the CCDs is at a temperature of
approximately -60C. The surface of the OBF has accumulated a layer of
contamination over the course of the mission. We have been characterizing the
thickness, chemical composition, and spatial distribution of the contamination
layer as a function of time over the mission. All three have exhibited
significant changes with time. There has been a dramatic decrease in the
accumulation rate of the contaminant starting in 2017. The lower accumulation
rate may be due to a decrease in the deposition rate or an increase in the
vaporization rate or a combination of the two. We show that the current
calibration file which models the additional absorption of the contamination
layer is significantly overestimating that additional absorption by using the
standard model spectrum for the supernova remnant 1E 0102.2-7219 developed by
the International Astronomical Consortium for High Energy Calibration. In
addition, spectral data from the cluster of galaxies known as Abell 1795 and
the Blazar Markarian 421 are used to generate a model of the absorption
produced by the contamination layer. The Chandra X-ray Center calibration team
is preparing a revised calibration file that more accurately represents the
complex time dependence of the accumulation rate, the spatial dependence, and
the chemical composition of the contaminant. Given the rapid changes in the
contamination layer over the past year, future calibration observations at a
higher cadence will be necessary to more accurately monitor such changes.Comment: 15 pages, 10 figures, SPIE Astronomical Instruments and Telescopes
2018, Conference Series, 1069
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