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Einstein Observatory (HEAO-2) Level 0 Data and Software at the HEASARC
L. Whitlock1 & M. Garcia2
The second High Energy Astrophysics Observatory (HEAO-2), launched by NASA on
13 November 1978, was renamed the Einstein Observatory after orbit was
achieved. It was the first fully imaging X-ray telescope put into space, with
an angular resolution of a few arcseconds, a field-of-view of tens of
arcminutes, and a sensitivity ~1000 times greater than any mission before it.
The mission ended in April 1981. The telescope had sensitivity over the energy
range 0.2-3.5 keV. The satellite contained a high resolution X-ray telescope
and focal plane assembly capable of positioning the focus at one of four
instruments: a high resolution imaging detector (HRI), a broader field imaging
proportional counter (IPC), a solid state spectrometer (SSS), and a Bragg
crystal spectrometer (FPCS). It also contained a monitor proportional counter
(MPC) aligned with the telescope, as well as a broad band filter spectrometer
(BBFS) and an objective grating spectrometer (OGS) to be used with the imaging
detectors. There was an active attitude control system capable of arcminute
pointing and arc second attitude determination.
The Einstein Level 0 data set now archived at the HEASARC contains raw,
telemetry data from the HRI and IPC detectors. These were two associated
instruments located at the focal plane.
The IPC was a position sensitive proportional counter which provided good
efficiency and full focal plane coverage, with moderate spatial and spectral
resolution. There were 2 such assemblies on Einstein, identical except
for the entrance window material. The IPC had a FOV of 75' x 75', with a
spatial resolution of ~1'. The effective detector area was ~100
and the time resolution was 63 msec. The energy range was 0.4-4.0 keV, and the
background countrate was ~ 10-2 cts/sec.
The HRI was a digital X-ray camera which provided high spatial and temporal
resolution over the central 25 arcmin of the Einstein focal plane. The
instrument had no inherent spectral resolution, but spectral studies could be
performed using an objective grating. There were 3 HRI detectors onboard,
identical except for the UV opaque shade material. The HRI had a 25' diameter
FOV, with a spatial resolution of 2" within 5' of the axis. The effective area
was 20 cm2 at 0.25 keV; 10 cm2
at 1 keV; and 5 cm2 at 2 keV. The time resolution was
8 msec. The energy range was 0.15-3.0 keV. The background was
~5 x 10-3 cts/arcmin2/sec.
Along with the data, the Pipeline processing system necessary to process the
data has also been installed at the HEASARC. This system consists of over
20,000 lines of Fortran and C code, and several INGRES databases describing
the data. The processing system performs all the steps needed to take raw,
telemetry data and produce a scientifically useful image for each observation.
Specifically, it determines and applies:
an aspect solution accurate to ~1"
barycenter time corrections
detector gain corrections, both temporal and spatial
The system is a direct port of the original Einstein Data Center Pipeline which
ran on the Data General computers, but now runs on Sparc platforms. The output
data formats are specific to the Pipeline system (i.e., .xpr files), but
routines exist in IRAF/PROS to convert them to standard FITS format. There is
extensive online documentation describing the data formats and how the system
runs. This documentation can be found in legacy anonymous ftp area under
The processing speed for the program has been increased by at least an order of
magnitude. Originally, it took about 1 year to process the 2.5 years of
Einstein data; now, on a small Sparc network, the same job takes only a few
weeks of computer time. One could conceive of deriving incrementally improved
calibrations (i.e., boresighting, flatfielding, gain corrections) and
reprocessing the data in order to make use of them.
To run the Pipeline software on the Level 0 data, the user must either come to
the HEASARC or work in conjunction with the HEASARC staff to put the required
data online. Unless requested, the database will reside on a shelf rather than
actively accessible in a jukebox. However, upon request, the data can be put
online in a matter of hours, and made available to the user.
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