The Einstein (HEAO-2) SSS and MPC Instruments


artist concept of HEAO-2 * High Level Data Products: These data have all been reformatted at the HEASARC. Data from these instruments are available on a CD-ROM entitled "The Einstein Observatory SSS, MPC, and FPCS Data Products" dated 1 June 1992 and created at the HEASARC. Notice that the SSS and MPC files have been slightly modified (and renamed) compared to the version on the CD-ROM to conform to the OGIP standards for spectra and lightcurves.

There are 635 distinct SSS observations in the HEASARC database. Available are the Einstein SSS spectral and rates file data products in (FITS and GIF format). Included with 605 (95%) of the SSS observations are the MPC data products (FITS files) for those cases where the MPC accumulated good data in the same time interval covered by the SSS observation. The remaining SSS observations cover time intervals in which all MPC data were flagged as bad by the pCHIP program that was used to generate the MPC spectra and lightcurves.

SSS Data

The Einstein Observatory Solid State Spectrometer (SSS) was operational from December 1, 1978 through October 3, 1979. It was the designated focal-plane instrument for 27 distinct time periods between these dates. The SSS response files incorporate the ice model described in the article on the SSS calibration by Christian, Swank and White that appeared in the HEASARC journal Legacy, No. 1. More information on the ice modeling procedure can be obtained in Arnaud, Szymkowiak, and White (1989, HEAO Newsletter, vol. 1, No. 2)

The total background due to all non-source contributions is 0.28 ct/s above 0.5 keV and 0.19 ct/s above 1 keV. Background is not measured simultaneously, and must be estimated from data accumulated over source-free exposures.

The cryogen keeping the SSS at its operational temperature of 100 K ran out, as expected, in October 1979, between Day 276 (Oct 3) and Day 286 (Oct 13). The small number of observations that were made after the cryogen was exhausted has been excluded from this database.

  • Spectra
    There is at least one spectrum per SSS observation of each target. If the observations covered an interval that extends over more than one (UT) day, then there is a spectrum accumulated for each day.

    There are 4 spectral data products associated with each SSS observation, identified by a unique file extension:

    • pha - the observed spectrum file
    • bck - the appropriate background file
    • cor - the appropriate correction file
    • rsp - the appropriate response file
    In addition there is a generic response file sss0.rsp which contains the response of the SSS to incident X-ray photons for the case when there is no ice build-up on the SSS detector, i.e. the zero-ice response file.
  • Rates
    There is 1 rate file for each SSS observation. This is a background-subtracted 81.92 s time resolution file in the 1.0-4.0 keV energy band covering the time interval of each spectrum.
MPC Data

  • Spectra
    There is one MPC spectrum accumulated to match each SSS spectrum. There are 2 spectral data products for each MPC observation:
    • pha - the observed spectrum file
    • bck - the appropriate background file
    In addition there is a generic response file mpc.rsp which contains the response matrix of the MPC, and is believed to be appropriate for the entire time period when the SSS was operational.
  • Rates
    There is one rates file for each quasi-simultaneous MPC observation. These are background-subtracted 40.96 s time resolution light curves in the 1.0-15.0 keV band covering the time interval of each spectrum. Note that, due to the differing instrumental observing constraints and particle background thresholds, the SSS and MPC data products are only quasi-simultaneous.

* Raw SSS data: The SSS instrument could be operated in any of 3 different data-gathering modes: PHA mode, DELTA-T mode, and MS mode. Within each mode different data-streams were obtained setting either different time resolution parameter and/or different number of energy channels. A typical Einstein SSS FITS raw data file contains ten extensions (eight dedicated to SSS data and two to the simultaneous MPC data set), all of them having the same FITS layout/structure. Within each SSS extension, stream of data, obtained within an observation, from the three different modes with 'similar' characteristics are combined together. The original datamode, therefore, is not unique within an extension. The files always contain the 10 extensions but not all the extensions contain data. The SSSRAW database records for each entry the number of rows present in the file for each extension. This allows a search for a particular data type. Listed below is a brief description of the different data types contained in the eight SSS extensions and the parameters which identified the extensions within this database :

---
 * 128 channel spectra accumulated either with a time resolution of 2.56,
   1.28 or 0.64 seconds (3 extensions).
   Parameters : SSS_SPEC_2_56S, SSS_SPEC_1_28S and MS
 * Intensity data over the full energy range with a time resolution of
   2, 5 and 10 ms (3 extensions).
   Parameters : SSS_TWO_MS, SSS_FIVE_MS and SSS_TEN_MS.
 * PHA values  of the first 512 events recorded in 1.28 seconds
   (1 extension). Parameter : RT_PHA
 * Histogram of 128 bins from the DELTA mode (1 extension).
   Parameter : DELTA
---
The MPC extensions contain the following data types associated to the following database parameters:
---
 * 8 channel spectra accumulated every 2.56 sec (1 extension).
   parameter : MPC_SPEC_2_56S.
 * Intensity value of the first 512 events recorded in 1.28 seconds
    parameter : MPC_TIP.
---

* Raw MPC data: The MPC Raw data set consists of about 19,000 FITS files each containing approximately 1200 2.56 second records. These files can be accesed via the MPCRAW database.


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