This Legacy journal article was published in Volume 3, May 1993, and has not been
updated since publication. Please use the search facility above to find regularly-updated information about
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The Release of the BBXRT Event Data
Alan P. Smale (LHEA)
The Broad Band X-ray Telescope, BBXRT, was flown on the Space Shuttle Columbia
as part of the Astro-1 payload in December 1990. During this mission it
performed 157 observations of 80 celestial X-ray sources ranging from stars,
CVs and X-ray binaries to clusters of galaxies and the X-ray background. BBXRT
has an energy range considerably broader than that of the Einstein SSS (0.3-12
keV) and a spectral resolution a factor of four improved over the EXOSAT and
Tenma Gas Scintillation Proportional Counters (9% at 1 keV; 2.5% at 6 keV). In
addition to the many scientific results derived from BBXRT data, the mission
also tested the on-orbit behavior of the novel thin-foil conical mirror
assembly and the broad-band solid-state detectors.
A previous article (Smale, 1992) gives a full description of the BBXRT
instrument, the mission, the list of sources observed, the detector response,
and a schedule for the release of BBXRT data to the community. This reference
also contains more detailed information about the point spread function,
detector background and alignment, and other analysis issues. It is assumed
here that the reader is familiar with this material.
2. The Data
The full BBXRT mission dataset is now available to the community. All products
are in standard FITS formats defined by the HEASARC, and the FITS headers
contain considerable explanatory information.
All items in the BBXRT archive are available via anonymous FTP from
legacy.gsfc.nasa.gov (220.127.116.11), and can be found in the `bbxrt'
directory. In addition, the observation catalog, spectra and light curves can
be examined using BROWSE in the HEASARC's on-line system, accessible on
Internet at ndadsa.gsfc.nasa.gov (18.104.22.168) or on DECnet at NDADSA (node
15761). From BROWSE, spectral fitting can be performed directly using XSPEC, or
the data products can be extracted and transferred back to the user's home
One data product has been generated per observation, slew or calibration
interval - 324 files per data type. The following types are available:
The `bbxrt/events' directory contains complete event lists for the whole
mission. The files contain one record per detected event; each record includes
the time, instrument, detector, PHA channel, and five data quality flags.
The `bbxrt/hk' directory contains housekeeping (hk) files for the relevant time
interval. The format for these files is identical to the standard ASCA format;
one record per parameter, with the values of the parameters listed at the
beginning of each file and only recorded thereafter when a value changes. The
parameters available are listed in Table 1. The maximum available time
resolution is 32 seconds for the first six parameters, 8 seconds for the last
two. For further information about these parameters, see Smale (1992).
MNEMONIC PARAMETER ACCEPTABLE RANGE
DETTA Temperature of the A detector 100K to 128 K
DETTB Temperature of the B detector 100K to 128 K
COVERA Cover A position monitor -5 to 110 % (100% = `cover on')
COVERB Cover B position monitor -5 to 110 % (100% = `cover on')
CALIBA Calibration source A position -5 to 110 % (100% = `source in')
CALIBB Calibration source B position -5 to 110 % (100% = `source in')
GUARDA Guard rate A > 0
GUARDB Guard rate B > 0
Files containing attitude information can be found in the `bbxrt/pointing'
directory. The time resolution is 1 second, and the parameters available are
RA and DEC (degrees, 1950.0) and the ROLL angle. These pointing data have an
accuracy of 10 arcminutes.
Mission Quality data
The `bbxrt/missqual' directory contains files with information about various
parameters that are important in assessing data quality. Available parameters
are listed in Table 2. The time resolution is 1 second. See Smale (1992) for
SUN ANGLE Sun angle from target in degrees (Target-BBXRT-Sun).
MOON ANGLE Moon angle from target in degrees (Target-BBXRT-Moon).
EARTH ANGLE Earth angle from target in degrees (Target-BBXRT-Earth
Bright/Dark Brightness/darkness of nearest limb.
Shuttle Day/Night Shuttle in day/night.
RAM ANGLE Velocity vector angle from target in degrees.
Spectra, background spectra, light curves and response matrices
The `bbxrt/spectra' directory contains source and background spectra, one per
pixel per observation, for each of the 157 source observations. The spectral
format conforms to the OGIP/HEASARC standard format (Arnaud et al.
1992). Light curves are similarly available in the `bbxrt/rates' directory.
BBXRT response matrix files are classified by off-axis angle rather than by
observation, since there were many observations performed at each given angle.
The `bbxrt/responses' directory contains one spectral response matrix per pixel
per unit off-axis angle between zero and 10 arcminutes, in the standard FITS
RMF (redistribution matrix file) format (George et al. 1992). The
correct off-axis angle for each spectrum can be found in its FITS file
To assist archival investigators who wish to examine large subsets of the BBXRT
archive, groups of the above files are available in compressed tarfiles. The
tar utility (allowing the collection and storage of a large number of files in
a single `tape archive' file) and the compression utility used are the standard
versions available on unix/ultrix systems. The `tar' directory contains two
subdirectories, `by_filetype' and `by_observation'. The former contains one
compressed tarfile per filetype for the following filetypes: spectra,
background spectra, light curves, HK files, mission quality files, pointing
files, and response matrices for a given off-axis angle. In the
`by_observation' directory users will find 157 tarfiles, each containing the
complete event list, HK data, mission quality data, pointing data, source and
background spectra, and rates files for one observation.
3. Analysis tools
The adoption of the FITS format makes the entire BBXRT dataset available in a
system-independent, self-describing format, and many institutions will have
their own suites of programs capable of reading data in this format. The FTOOLS
software, designed and written by the HEASARC/ASCA project, are now available
to help users manipulate FITS files and analyze the data they
contain. The software runs both under IRAF and as a series of standalone tasks,
and a user-friendly command-driven top level program called XSELECT is
currently being tested.
Arnaud, K.A., George, I.M. & Tennant, A.F., 1992, Legacy, 2,
George, I.M., Arnaud, K.A., Pence, B. & Ruamsuwan, L., 1992, Legacy,
Smale, A.P., 1992, Legacy, 2, 17.
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