sssarf -- creates an Ancilliary Response File (ARF) for Einstein SSS PHA data
phafile calfexp outfile1 (arfversn) (oddeven) (icef) (chatter) (mode)
This task creates an Ancilliary Response File (ARF) appropriate for a user-defined PHA file from the Solid State Spectrometer (SSS) onboard the Einstein Observatory. The task calculates the ARF, taking into account the area of the X-ray telescope, AND corrections for the time-dependent build up of water ice on the front of the detector.
The Solid State Spectrometer was a croygenically cooled detector. Cooling was obtained by attatching the SSS to a cold plate within a cryostat containing methane and ammonia. Unfortunantely, cryopumping of outgassing material lead to a time-dependant build up of water-ice on the detector surface, giving a much lower energy response than expected. A heater attatched to the cold plate enabled the SSS to be periodically de-frosted. After each defrost, a fraction of the defrosted water ice escaped out of a small opening in the cryostat to outer space; however ice returned after 12-24 hrs due to the residual water. As the number of defrosts performed increased, the total amount of ice return after each defrost was reduced, until after 10 months (Dec 1978 - Oct 1979) the amount of ice on the front of the detector was negligable. Two efforts, in 1979 and 1990, have been made to understand the SSS response matrix. Many observations between Dec 1978 and Oct 1979 of sources with simple, well-known spectra were used to determine the variation in the amount of ice as a function of time. This lead to the development of an ice-model consisting of two distinct components with e-folding return times of 0.25 and 10 days (D.J. Christian et al., "The Einstein SSS Calibration", Legacy, 1992, No. 1, p38-42). The model includes the effects of the defrosts and produces an estimate of the amount of ice accumulated at any given epoch.
SSSARF calculates the epoch of every sub SSS observation within the input source PHA file, and enters this value into the above ice-model to determine the amount of ice. Using this 'ice-parameter' and the energy bounds read from the input RMF, the level of ice absorption at each energy is determined. All i/p must be in an OGIP-approved FITS file format (i.e. PHAVERSN = 1992a, RMFVERSN = 1992a) and therefore consist of:
(i) an EINSTEIN SSS PHA file for a given source observation.
(ii) an EINSTEIN SSS Detector Restribution Matrix File (RMF) containing information concerned with the photon redistribution process ONLY (i.e. detector gain and energy resolution). Two RMFs are currently available via anonymous ftp to the HEASARC Calibration database (ftp://heasarc.gsfc.nasa.gov/caldb/data/einstein/sss/cpf/*.rmf). The recommended RMF for use with this task is that which has been corrected for the 'odd/even' effect (whereby the original elements in the SSS detector redistribution matrix are multiplied by 1.000000 for odd-numbered channels, and 1.029390 for even-numbered channels). A corresponding dataset, without corrections for the `odd/even' effect may also be used. It should be stressed that neither RMF contains any corrections for the water ice on the front of the detector.
An output Ancilliary Response File (ARF) appropriate to the source observation is generated. This dataset contains a 1-D (energy) FITS extension containing the product of the SSS geometric area (180cm**2) and the ice-absorption at each energy. Finally, the source PHA file is updated by writing the names of the input RMF and the output ARF to the keywords RESPFILE and ANCRFILE respectively. Comment lines are also written giving overall mean epoch and mean ice values for the observation.
Lorraine Breedon HEASARC NASA/GFSC http://heasarc.gsfc.nasa.gov/cgi-bin/ftoolshelp