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SSS - Einstein SSS Spectra and Lightcurves



This table is the Einstein Solid State Spectrometer catalog of observations and data products. It incorporates the most recent ice model that is described in the article on the SSS calibration by Christian, Swank, and White that appeared in the HEASARC journal, Legacy, No. 1. Also available as "associated" data products are the quasi-simultaneous observations made by the Einstein Monitor Proportional Counter. There are 634 distinct SSS observations in this database, 95% of which have associated MPC data products. The remaining SSS observations cover time intervals in which all MPC data was flagged as bad by the pCHIP program that was used to generate the MPC spectra and lightcurves.


"SSS - The _Einstein_ Solid State Spectrometer Database at the HEASARC", by S. Drake, K. Arnaud, and N. White, Legacy, #1, May 1992.


The SSS consisted of a cryogenically cooled Si(Li) detector at the focus of the Einstein Observatory. It subtended a six arcminute-diameter circular aperture and was slightly defocused so that a point source is blurred to a radius of about one arc minute. It exhibited a noise-limited spectral resolution of about 160 eV full width half maximum, which is nearly energy independent over the sensitive energy range of 0.5 - 4.5 keV. Each photon is pulse height analyzed into one of 128 bins, each 45 eV wide.

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.

A time-dependent build-up of ice (water) on the detector surface occurred because of cryo-pumping of ambient outgassing material onto the 100 K detector. It was periodically defrosted by heating to 220 K at the beginning of a series of three days of observations. Each defrost reduced the total amount of ice that returned, such that after 9 months the ice covering was almost gone. The ice covering is parametrized by an ice parameter that varies from a low value of 0.05 to a high early on of 4.58. A model has been developed that predicts the ice parameter as a function of time, and is used to obtain the correct response matrix for any given observation. The uncertainty in this ice parameter varied throughout the operational lifetime, and was greatest at the beginning. More information on the ice modeling procedure can be obtained in Arnaud, Szymkowiak, and White (1989, HEAO Newsletter, Vol. 1, No. 2) and Christian, Swank, and White (1992, Legacy: the HEASARC Newsletter, Vol. 1, No. 1).

The cryogen keeping the SSS at its operating temperature of 100 K ran out, as expected, in October 1979, and no more observations were possible.

Data Products

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. The spectra are not background-subtracted. Detector response matrices and background spectra are made using either the VIMAT program or the XSPEC command.

Lightcurves: There is a background-subtracted 81.92 s time resolution light curve in the 1.0-4.0 keV band covering the time interval of each spectrum.

Associated Products: The Einstein monitor proportional counter, MPC, operated in the 1-15 keV band, with eight pulse height channels. It was a mechanically collimated detector with a full width half maximum field of view of 45 arc minutes.

There is one MPC spectrum accumulated to match each SSS spectrum (with the small number of exceptions noted above where there are no matching MPC observations). The spectra are not background-subtracted. Background spectra and the detector response matrix (the latter is considered to be valid for the entire mission) can be extracted using the VIMAT program.

There are also background-subtracted 40.96 s time resolution light curves in the 1.0-15.0 keV band covering the time interval of each spectrum.

Notice that, due to the differing instrumental observing constraints and particle background thresholds, the SSS and MPC data products are only quasi-simultaneous. The start and stop times referred to in the parameters description refer specifically to the SSS observations.


Associated lightcurve names

Associated file response

The root name of the files containing the MPC spectrum (.pha).

The Galactic latitude and of the pointing.

The HEASARC BROWSE Class of the target. (This classification scheme is described in detail in the HEASARC document `Available Databases`).


The count rate in the 0.6 to 4.5 keV band. Note that the count rate is affected by the ice accumulating on the detector, and will change from observation to observation because of this. Two other count rates are available:

   * min_count_rate - minimum count rate during the observation,
   * max_count_rate - maximum count rate during the observation.

Count Rate Error


The Declination of the pointing.

The change in ice parameter across the spectral accumulation time.

The end time of the SSS observation in the same format.

The total on source time, corrected for dead time.

The root name of the files containing the SSS lightcurves (.rbf).

The root name of the files containing the SSS spectrum (.pha) and lightcurves (.rbf).

The root name of the files containing the SSS spectrum (.pha).

flux (0.5-4.0 keV) (Note: All values are zero as populated.)

The value of the ice parameter at the start of the spectral accumulation.

The value of the ice parameter at the end of the spectral accumulation. If there is a large jump in the ice parameter (10 percent or more) then the ice build-up occurred rapidly, and the spectral fits at less than 1 keV may not be reliable.

good c

Length of assoc lightcurves

Length of assoc spectra

The Galactic longitude of the pointing.

Length of lightcurves

Length of spectra

Maximum count rate

Error on maximum count rate

Minimum count rate

Error on minimum count rate

Number of assoc lightcurves

The name of the nominal SSS target. We have tried to select the most commonly used name in all cases, but this of course is somewhat a matter of opinion. (Note that the names contain embedded blanks, e.g., Cyg X-1)

Number of assoc spectra

Number of lightcurves

Number of spectra

The Right Ascension of the pointing.


This is the Einstein Sequence Number for the observation.

The `tchi2` parameter is a chi2 test to a constant source intensity.

The start time of the SSS observation.

This is a classification made by Jean Swank and Damien Christian as to the nature of the source. The following types have been defined:

     'BES'     for X-ray binary with Be star primary: e.g., Gam Cas.
     'BLK'     for X-ray binary with black hole primary: e.g., Cyg X-1.
     'CLUSTER' for cluster of galaxies: e.g., A 2029.
     'CVS'     for cataclysmic variable: e.g., AM Her.
     'GAL'     for galaxy or quasar: e.g., 3C273.
     'LMXB'    for low-mass X-ray binary: e.g., Cyg X-2.
     'PULSAR'  for pulsar: e.g., Cen X-3.
     'RSCVN'   for RS CVn active binary system: e.g., AR Lac.
     'SNR'     for supernova remnant: e.g., sn 1006.
     'STAR'    for miscellaneous varieties of galactic stars not belonging to the
                   other stellar categories: e.g., tau Sco.
     'MISPT'   for observations made at incorrect coordinates (i.e., mispoints).

The year of the observation.

Contact Person

Questions regarding the SSS database table can be addressed to the HEASARC User Hotline.
Page Author: Browse Software Development Team
Last Modified: Friday, 20-Mar-2015 18:39:45 EDT