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Calibration Files for Standard Data Processing



The PSPC as part of the focal plane instrumentation of the XRT\ has been thoroughly calibrated using ground based as well as in-flight measurements. These results are used during the SASS processing (cf. module CT of the TEL processing in Section 8.2.2) to correct the recorded raw event information (RAWX, RAWY, and PHA = RAW_AMPL) for temporal and positional variations, saturation effects, and non-linearities of the PSPC and its following electronics yielding the corrected event (XDET, YDET, and PI = AMPL). A complete record of an event delivered by the standard processing is then labeled (RDF format) together with a corrected event time (see Section 3.8) and sky coordinates determined from the attitude solution (see Chap. 2.2) as (TIME, XDET, YDET, AMPL, XPIX, YPIX).         


Shortcut CT task description and dependencies name of calibration file
BAL CTA bin of Al K tex2html_wrap_inline18249 line (Prescott fit) steering database (INGRES )
NLC CADC correction for ADC non-linearity p$manpar:adc_bins.dat
GSC CGS correction for gain saturation (none)
TGC CTG correction for temporal gain variations (none)
EPC DCORE electronic position correction p$manpar:para_c.dat
tex2html_wrap_inline18257 p$manpar:senk_c.dat
SGC DCORG correction for spatial gain variations p$manpar:gain_kor3_c.dat
tex2html_wrap_inline18259 p$manpar:gain_kor3_b.dat
WC DCORW window correction p$manpar:tabx_093_c.dat
tex2html_wrap_inline18261 p$manpar:taby_093_c.dat
FC FCOR field correction v$manpar:onax.dat
Table F.1:   Corrections to the raw detector output information, listed in the order in which the corrections are applied.


here SASS CT RDF format short description
tex2html_wrap_inline18267 A RAW_AMPL ADC pulse height channel of event (integer in [1,256])
tex2html_wrap_inline18271 AN pulse height of event, corrected for ADC non-linearity
tex2html_wrap_inline18273 ANG pulse height of event, corrected for ADC non-linearity and gain saturation
tex2html_wrap_inline18275 ANGT pulse height of event, corrected for ADC non-linearity, gain saturation, and temporal variations
tex2html_wrap_inline18277 ANGG AMPL pulse height of event, corrected for ADC non-linearity, gain saturation, temporal and spatial variations (PI channel)
tex2html_wrap_inline18279 IX_EV RAWX raw detector x coordinate (integer number in [1,8192])
tex2html_wrap_inline18285 IY_EV RAWY raw detector y coordinate (integer number in [1,8192])
tex2html_wrap_inline18291 XE, YE detector coordinates (electronic position correction applied)
tex2html_wrap_inline18293 XW, YW detector coordinates (electronic position correction and window correction applied)
tex2html_wrap_inline18295 XC, YC XDET, YDET detector coordinates (electronic position correction, window correction and correction for XRT field distortion applied)
tex2html_wrap_inline18297 FAK PHA channel of the Al K tex2html_wrap_inline18299 line (BAL ) (from Prescott fit)
tex2html_wrap_inline18301 GAIN correction factor for temporal gain variations (close to 1; gain saturation is taken into account)
r RAN random number (real number in [0.0,1.0])
SASS convention short description


corresponds to   tex2html_wrap_inline18309
tex2html_wrap_inline18311 corresponds to   tex2html_wrap_inline18313
x' corresponds to a simple transformation of  x  (`modified x')
Table F.2:   Parameters and conventions used by SASS

The raw event is actually triggered by an incoming X-ray photon scattered off the XRT mirror is passing through the PSPC window framed by the support structure. This process is described by the effective area of the XRT and the window transmission of the PSPC. Then the photon is absorbed by the counter gas of the PSPC\ (cf. Fig. 3.1) and yields a (primary) electron  which is thermalized and causes secondary ionization of the counter gas. The electron cloud  drifts through the K1 cathode grid (25 strips) towards the A1 anode grid. When close enough to an anode wire the charge cloud can be amplified by a (gain) factor of tex2html_wrap_inline18321 because the electric field strength becomes sufficiently high. This avalanche of charge onto the anode leads to a charge pulse at the anode A1 and an induced signal is detected at the cathode K1 and K2 which are aligned perpendicular to each other to determine the position of the photon inside the detector. Typically two to five wires are excited by a signal which is digitized by means of pulse shapers, peak detectors, and ADCs. After validity checking the event position  is calculated by a centre of gravity determination. The signal caused by the photon inside the detector is described by the quantum efficiency of the counter gas and the gain, which depends on the gas state and the HV of the anode.  

SASS processing stores the raw event information in the file TRGEV.TEL and module CT converts this into the files CTEV.TEL (for target events), CCEV.TEL (for calibration events), NOSEV.TEL (for non-scientific events like filter-wheel-closed position), RDAT5.TEL (for screened events due to housekeeping status).

The following sections summarize comprehensively the present state of the correction, whose individual steps are listed in Table F.1. Parameters and conventions often used in these sections are collected for a better overview in Table F.2.

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