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X-Ray Background Data Sets at the HEASARC
The HEASARC has the following data sets which contain measurements of the
X-ray background all-sky intensity and/or spectra obtained with different
experiments, listed in inverse chronological order (most recent first):
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ROSAT All-Sky Survey (RASS)
These maps of the diffuse X-ray background
(`ROSAT Survey Diffuse Background
Maps, Paper II', S. L. Snowden, R. Egger, M. J. Freyberg, D. McCammon, P. P.
Plucinsky, W. T. Sanders, J. H. M. M. Schmitt, J. Trümper, and W. Voges,
ApJ, Vol. 485 (1997), pp. 125-135) are used by the
HEASARC's X-Ray Background Tool (XBT). This tool calculates for a
specified astronomical position and either a circle with a specified radius
or an annulus with specified inner and outer radii centered on this position
the average X-ray background count rate and statistical uncertainty in each
of the six standard bands of the ROSAT All-Sky Survey diffuse background maps
(R1, R2, R4, R5, R6, R7). In addition, the average count rates are given for
the combined 1/4 keV (R1 + R2), 3/4 keV (R4 + R5), and 1.5 keV (R6 + R7)
bands. (The count rates for the combined bands are simply the sum of the
count rates for each component band, and the uncertainty in the combined
band count rate is the square root of the sum of the squares of the
uncertainties of each component band). A full description of the use
of these maps is given in the XBT help
documentation.
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Diffuse X-Ray Spectrometer (DXS)
The DXS experiment was flown on the space shuttle Endeavour from January 13
through 19, 1993. DXS was developed by the University of Wisconsin and its PI
was Dr. Wilt Sanders. The only DXS data that the HEASARC presently has,
the so-called level 1 reduced data products, are stored in
this directory in the
form of gzipped FITS files.
The naming convention of the files is of the form "orbitNN_TYPE_SIDE.fits.gz",
where NN = 2-digit orbit number in the range 1 to 91, TYPE = 3 or 4 character
type of data file, out of the set:
sci - science X-ray event data
fast - engineering/housekeeping data (1 record per sec)
slow - more engineering/housekeeping data (1 record per 4 secs)
time - time records
spoc - spoc (shuttle payload of opportunity carrier) information
cmd - commands uploaded during this orbit
orb - orbit information
and SIDE = 1-character indicator of the DXS instrument that the data are
from:
p - Port instrument
s - Starboard instrument
and the final .gz indicates that the file has been gzipped. These files can
be read using standard FITS readers such as fdump.
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The SAS-3 low-energy detector
This directory
contains the all-sky image from the SAS-3 low-energy X-ray
detector in the C band (0.10-0.28 keV in FITS format. These data were
discussed in the paper by Marshall and Clark (1984, ApJ, 287, 633-652: see
the ADS abstract appended below). The file sas.fits contains the all-sky
intensity map in Galactic coordinates in an Aitoff projection centered
on the Galactic Center.
Title: SAS 3 survey of the soft X-ray background
Authors: Marshall, F. J.; Clark, G. W.
Publication: Astrophysical Journal, Part 1, vol. 287, Dec. 15, 1984, p.
633-652.
Abstract: The results of a survey of the soft X-ray sky in the C band (0.10 -
0.28 keV) are reported. The observations were carried out using two independent
flow proportional counters on board the SAS 3 X-ray satellite which had a
total angular resolution of 2.9 deg FWHM, and a total exposure of 22,000 cm^2
s sr. It is found that C band counting rates were generally inversely
correlated with the column density of the neutral hydrogen on all
angular scales down to the lowest angular resolution of the detectors. In the
region 90-180 degrees Galactic longitude and 0-90 degrees Galactic
latitude, the relation between C-band rates and the column densities of
neutral hydrogen was fitted with a residual rms deviation of less than 13%
by a two-component numerical model of the X-ray background. For the apparent
attenuation column density, a value of 2.7 x 10^20 per sq cm was obtained.
On the basis of a computer simulation of the SAS 3 data, it is shown that
the observed clumping of interstellar matter was consistent with the
magnitude of spatial fluctuations in the C-band map. When the background
rates were subtracted from the survey map, the subsequent map showed
foreground emission and absorption features with improved sensitivity and
clarity. A series of computer-generated maps incorporating the SAS 3 data
is given in an appendix.
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The HEAO 1-A2 experiment
This directory
contains the spectra (and response matrices) of the X-ray
background obtained with the HEAO1 A2 experiment (Marshall et al., 1980, ApJ,
235, 4). The spectra and responses are all in FITS formats:
hed11c.pha h111095c.rsp HED1 M1
hed12c.pha h121095c.rsp HED1 M2
hed31c.pha h31257c.rsp HED3 M1
hed32c.pha h321095c.rsp HED3 M2
med1c.pha m11n.rsp MED M1
med2c.pha m12n.rsp MED M2
The
led sub-directory contains the A2 LED C-band (0.25 keV) All-Sky map
of the soft X-ray diffuse background (Garmire et al. 1992, ApJ, 399, 694)
in FITS format.
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The University of Wisconsin experiments flown on 10 sounding rockets in the
period from 1972 to 1980
This
directory contains the all-sky images from the University of Wisconsin
experiments flown on 10 sounding rockets over the period from 1972 to 1980.
All of the files are in FITS format. These data were discussed in the paper
by McCammon et al. (1983, ApJ, 269, 107-135: see the ADS abstract appended
below). The 52 files comprise 26 pairs of different visualizations of the
soft X-ray diffuse background, corresponding to different energy bands and
projections, the rat.fits files containing the intensity maps, and the
sig.fits files containing the uncertainty maps. The first part of the file
names codes the X-ray band to which it corresponds as follows:
Wisconsin Band Energy Range in eV
B 130 - 188
C 160 - 284
M1 440 - 930
M2 600 - 1100
I 770 - 1500
J 1100 - 2200
2-6 1800 - 6300
The second part of the file names codes the all-sky projection used as
follows (all maps are in Galactic coordinates):
Code Projection
0 Aitoff centered on Galactic Longitude = 0 degrees
180 Aitoff centered on Galactic Longitude = 180 degrees
npol Polar equal-area centered on North Galactic Pole
spol Polar equal-area centered on South Galactic Pole
Title: The soft X-ray diffuse background
Authors: McCammon, D.; Burrows, D. N.; Sanders, W. T.; Kraushaar, W. L.
Publication: Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 269, June 1,
1983, p. 107-135.
Abstract: Maps of the diffuse X-ray background intensity covering essentially
the entire sky with approximately 7 degree spatial resolution are presented
for seven energy bands. The data were obtained on a series of ten sounding
rocket flights conducted over a seven-year period. The different nature of
the spatial distributions in different bands implies at least three distinct
origins for the diffuse X-rays, none of which is well-understood. At energies
of approximately 2000 eV, an isotropic and presumably extragalactic 500 and
1000 eV, an origin which is at least partially galactic seems called for.
At energies 284 eV, the observed intensity is anticorrelated with neutral
hydrogen column density, but we find it unlikely that this anticorrelation
is simply due to absorption of an extragalactic or halo source. Previously
announced in STAR as N83-20892.
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