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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 cm2, 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
	detector backgrounds
	source detection

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 /FTP/einstein/doc/level0.

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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