%+
% Name:
%   memo_event_status_bits_2.0.tex
%
% History:
%   06 Jul 00, created, Glenn E. Allen
%   24 Jul 00, revised, GEA
%   18 Jul 01, added bit 20, GEA
%   05 Mar 02, changed bit 12/13 description, GEA
%   09 May 02, added bits 23 (v1.4), GEA
%   17 Jul 02, fixed a slight inaccuracy in bit 1 (v1.5), GEA
%   10 Sep 02, updated header (v1.5b), GEA
%   18 Oct 02, slight change for bit 5 (v1.6), GEA
%   05 Mar 03, clarified bit 1 (v1.7), GEA
%   17 Nov 05, disabled bits 12 and 13 (v1.8), GEA 
%   29 Mar 06, added the tool which sets them (v1.9), GEA
%   06 Apr 06. added Table 3 (v2.0), GEA
%-

\documentclass{article}

\usepackage{changebar}
\usepackage{cxo-memo-logo,gea}
\usepackage[dvips]{graphics}

\begin{document}

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\memobasic{
   Jonathan McDowell, SDS Group Leader }{
   Glenn Allen, SDS ACIS Scientist }{
   ACIS Event Data STATUS Bits }{
   2.0 }{
   http://space.mit.edu/CXC/docs/docs.html\#evtbits }{
   /nfs/cxc/h2/gea/sds/docs/memos/memo\_event\_status\_bits\_2.0.tex }

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\vspace*{0.3in}
%
The thirty-two bits of the column STATUS of an ACIS event file (e.g.\ evt1 
or evt1a) are used to indicate various potential problems with the events.  
If one or more of the bits is set to a value of one for an event, the event 
may have a problem and is excluded from the Level 2 ACIS event file (i.e.\ 
evt2).  This memo describes the conditions for which a bit is set to one
(Table~1), the tool which sets each bit (Table~2) and the conditions for
which a bit is set to zero on input (Table~3).

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% STATUS bits

\section{STATUS bits}

\begin{table}[h]
\begin{center}
\begin{tabular}{|c|c|l|}
\multicolumn{3}{c}{Table 1} 
  \\
\hline
STATUS
   & Integer
   & 
   \\
Bit
   & Representation$^{\dag}$
   & \hfil Condition(s) for which the STATUS bit is set to one \hfil
   \\
\hline
\
   & 
   &
   \\
0
   & 1
   & \parbox[t]{4.47in}{
     The CHIPX and CHIPY coordinates of an event are invalid (e.g.\ the
     coordinates are outside a window, are on an inactive CCD, or are in the
     top-half of a CCD experiencing a ``FEP0'' problem). 
     \\
     }
   \\
1
   & 2
   & \parbox[t]{4.47in}{
     The PHA value of the central pixel of an event island is less than (or,
     in some cases, less than or equal to) one or more of PHA values of the
     eight surrounding pixels in the event island (before the CTI adjustment
     is applied) or is less than the split threshold (not the event threshold).
     \\
     }
   \\
2
   & 4
   & \parbox[t]{4.47in}{
     One or more of the nine pixels of a $3 \times 3$-pixel event island has
     a PHA value $> 4095$ after the bias and the delta overclock values have
     been subtracted.
     \\
     }
   \\
\hline
\end{tabular}
\end{center}
\end{table}

$^{\dag}$ This integer representation is appropriate for machines that use the
``big-endian'' convention for byte strings, where the first byte of the string
is assumed to contain the highest-order bits.

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\begin{table}[h]
\begin{center}
\begin{tabular}{|c|c|l|}
\multicolumn{3}{c}{Table 1 cont.} 
  \\
\hline
STATUS
   & Integer
   & 
   \\
Bit
   & Representation
   & \hfil Condition(s) for which the STATUS bit is set to one \hfil
   \\
\hline
\
   & 
   &
   \\
3
   & 8
   & \parbox[t]{4.47in}{
     The sum of the PHA values of the nine pixels of a $3 \times 3$-pixel 
     event island that are $\ge$ the split threshold $\ge 32767$ (i.e.\
     $\gtapprox\ 130$~keV).
     \\
     }
   \\
4
   & 16
   & \parbox[t]{4.47in}{
     The CHIPX and CHIPY coordinates of an event are the coordinates of a 
     pixel that is identified as ``bad'' in the associated bpix1 file.
     \\
     }
   \\
5
   & 32
   & \parbox[t]{4.47in}{
     The CHIPX and CHIPY coordinates of one or more of the outer eight
     pixels of a $3 \times 3$-pixel event island (or the outer twenty-four
     pixels of a $5 \times 5$-pixel event island) are the coordinates of a
     pixel that is identified as ``bad'' in the associated bpix1 file.
     \\
     }
   \\
6
   & 64
   & \parbox[t]{4.47in}{
     The bias value associated with the CHIPX and CHIPY coordinates of an 
     event $= 4095$.  This condition occurs if the pixel is identified as 
     ``bad'' or if the pixel is not on the active region of a sub array.
     \\
     }
   \\
7
   & 128
   & \parbox[t]{4.47in}{
     The bias value associated with the CHIPX and CHIPY coordinates of an 
     event is unknown (e.g.\ telemetry was lost).
     \\
     }
   \\
8
   & 256
   & \parbox[t]{4.47in}{
     The bias value associated with the CHIPX and CHIPY coordinates of an 
     event $= 4094$.  This condition indicates that the pixel has a
     bias-parity error.
     \\
     }
   \\
9
   & 512
   & \parbox[t]{4.47in}{
     The overclock value associated with an event is unknown.
     \\
     }
   \\
10
   & 1024
   & \parbox[t]{4.47in}{
     The overclock value associated with an event is not in the nominally-
     expected range of overclock values.
     \\
     }
   \\
11
   & 2048
   & \parbox[t]{4.47in}{
     The mean PHA value of the four corner pixels of a $3 \times 3$-pixel 
     event island $ < -4095$.
     \\
     }
   \\
12 
   & 4096
   & \parbox[t]{4.47in}{
     Bits 12 and 13 are used for TIMED GRADED mode observations to indicate
     the number of pixels that were included in the computation of the mean
     PHA value of the four corner pixels of a $3 \times 3$-pixel event
     island.  Bits (12,13) have values of (0,0), (1,0), (0,1), or (1,1) to
     indicate that 4, 3, 2, or 1 pixels were used to compute the mean value
     of the corner pixels, respectively. Pixels are excluded from the
     computation if they are identified ``bad'' or have bias-parity errors.
     [Obsolete.  The use of this bit has been discontinued.]
     \\
     }
   \\
13
   & 8192
   & \parbox[t]{4.47in}{
     See STATUS bit 12.  [Obsolete.  The use of this bit has been
     discontinued.]
     \\
     }
   \\
14
   & 16384
   & \parbox[t]{4.47in}{
     The mean value of the four corner pixels of a $3 \times 3$-pixel event
     island $= 4095$. This condition indicates that all four of the corner
     pixels are ``bad'' or have bias-parity errors.
     \\
     }
   \\
15
   & 32768
   & \parbox[t]{4.47in}{
     The event is associated with a horizontal ``streak'' on a CCD.  Streaks
     are associated with spurious signals in the read-out electronics.
     \\
     }
   \\
16
   & 65536
   & \parbox[t]{4.47in}{
     Bits 16--19 are used to indicate that an event may be part of a 
     ``cosmic-ray afterglow.'' The bits enumerate the number of consecutive
     frames (including the frame associated with the event) in which events
     have been reported at the same CHIPX and CHIPY location as the given
     event.  
     \\
     }
   \\
\hline
\end{tabular}
\end{center}
\end{table}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\begin{table}[t]
\begin{center}
\begin{tabular}{|c|c|l|}
\multicolumn{3}{c}{Table 1 cont.} 
  \\
\hline
STATUS
   & Integer
   & 
   \\
Bit
   & Representation
   & \hfil Condition(s) for which the STATUS bit is set to one \hfil
   \\
\hline
\
   & 
   &
   \\
16 cont.
   & 65536
   & \parbox[t]{4.47in}{
     For example, if bits 16--19 are 1100, 1010, or 1111, the event
     is part of a sequence of 3, 5, or $\ge 15$ events at the same CHIPX and
     CHIPY location, respectively.
     \\
     }
   \\
17--19
   & ---
   & \parbox[t]{4.47in}{
     See STATUS bit 16.
     \\
     }
   \\
20
   & 1048576
   & \parbox[t]{4.47in}{
     The CTI-adjustment algorithm (if used) did not converge.
     \\
     }
   \\
21
   & 2097152
   & \parbox[t]{4.47in}{
     An event in a read-out streak is identified as a source event.
     \\
     }
   \\
22
   & 4194304
   & \parbox[t]{4.47in}{
     An event in a read-out streak is identified as a background event.
     \\
     }
   \\
23
   & 8388608
   & \parbox[t]{4.47in}{
     The event is identified as a potential cosmic-ray background event.
     This bit can be set to one only for TIMED VFAINT mode data that was
     processed using the optional \ape\ parameter check\_vf\_pha$=$yes.
     \\
     }
   \\
24--31
   & ---
   & \parbox[t]{4.47in}{
     Unused.
     \\
     }
   \\
\hline
\end{tabular}
\end{center}
\end{table}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\begin{table}[h]
\begin{center}
\begin{tabular}{|c|c|l|}
\multicolumn{3}{c}{Table 2}
  \\
\hline
STATUS
  & Integer
  &
  \\
Bit
  & Representation
  & \hfil Tool which sets the bit(s) \hfil
  \\
\hline
\
   & 
   &
   \\
0
  & 1
  & \parbox[t]{4.47in}{ acis\_format\_events \\ }
  \\
1--5
  & ---
  & \parbox[t]{4.47in}{ acis\_process\_events \\ }
  \\
6--10
  & ---
  & \parbox[t]{4.47in}{ acis\_format\_events \\ }
  \\
11--13
  & ---
  & \parbox[t]{4.47in}{ ? \\ }
  \\
14
  & 16384
  & \parbox[t]{4.47in}{ acis\_process\_events \\ }
  \\
15 
  & 32768
  & \parbox[t]{4.47in}{ destreak \\ }
  \\
16--20
  & ---
  & \parbox[t]{4.47in}{ acis\_process\_events \\ }
  \\
21--22
  & ---
  & \parbox[t]{4.47in}{ acisreadcorr \\ }
  \\
23
  & 8388608
  & \parbox[t]{4.47in}{ acis\_process\_events \\ }
  \\
24--31
  & ---
  & \parbox[t]{4.47in}{ None \\ }
  \\
\hline
\end{tabular}
\end{center}
\end{table}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\begin{changebar}
\begin{table}[h]
\begin{center}
\begin{tabular}{|c|c|l|}
\multicolumn{3}{c}{Table 3} 
  \\
\hline
STATUS
   & Integer
   & 
   \\
Bit
   & Representation
   & \hfil Condition(s) for which the STATUS bit is set to zero on input \hfil
   \\
\hline
\
   & 
   &
   \\
0
   & 1
   & \parbox[t]{4.47in}{
     Never unset this bit on input.
     \\
     }
   \\
1--3
   & ---
   & \parbox[t]{4.47in}{
     ?
     \\
     }
   \\
4--5
   & ---
   & \parbox[t]{4.47in}{
     Always unset these bits on input.
     \\
     }
   \\
6--10
   & ---
   & \parbox[t]{4.47in}{
     Never unset these bits on input.
     \\
     }
   \\
11
   & 2048
   & \parbox[t]{4.47in}{
     ?
     \\
     }
   \\
12--13
   & ---
   & \parbox[t]{4.47in}{
     Always unset these bits on input.
     \\
     }
   \\
14
   & 16384
   & \parbox[t]{4.47in}{
     ?
     \\
     }
   \\
15
   & 16384
   & \parbox[t]{4.47in}{
     Always unset this bit on input.
     \\
     }
   \\
16--19
   & ---
   & \parbox[t]{4.47in}{
     Always unset these bits on input.
     \\
     }
   \\
20
   & 1048576
   & \parbox[t]{4.47in}{
     Refer to the latest revision of the spec entitled ``Adjusting ACIS
     Event Data to Compensate for CTI.''
     \\
     }
   \\
21--22
   & ---
   & \parbox[t]{4.47in}{
     Always unset these bits on input.
     \\
     }
   \\
23
   & 8388608
   & \parbox[t]{4.47in}{
     Always unset this bit on input.
     \\
     }
   \\
\hline
\end{tabular}
\end{center}
\end{table}
\end{changebar}

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