OGIP Calibration Memo CAL/GEN/92-002

The Calibration Requirements for Spectral Analysis
(Definition of RMF and ARF file formats)

THE CALIBRATION REQUIREMENTS FOR SPECTRAL ANALYSIS

(Definition of RMF and ARF file formats)

Ian M. George, Keith A. Arnaud, Bill Pence, Laddawan Ruamsuwan & Michael F. Corcoran
Code 662,
NASA/GSFC,
Greenbelt, MD20771
Version: 2007 Nov 01





SUMMARY

The approach and calibration file formats adopted by the HEASARC for spectral analysis of X-ray PHA datasets are outlined and discussed.
Intended audience: primarily HEASARC programmers, hardware teams & authors of spectral analysis s/w.
Note: There is an addendum to this memo, CAL/GEN/92-002a which should also be referred to.

LOG OF SIGNIFICANT CHANGES


Release Sections Changed Brief Notes
Date
1992 Oct 07 Original Version
1995 Jan 11 All Made compatible with LaTeX2HTML s/w
1998 Dec 19 All HDUVERS=1.3.0 of the RMF matrix extension
Compatibility with OGIP/92-002a
2005 Feb 15 From KAA: fixed some ambiguities
2005 Jul 05 2 MFC: describe more fully how RMF and ARF are related
2007 Nov 1 §§ 3.2.1, 3.2.2 MFC: allowed Fchan, Nchan and Chan to be 4 byte integers (From KAA)

Contents

1  INTRODUCTION
2  OVERVIEW
    2.1  The Redistribution Matrix
    2.2  Detector Sensitivity, or Ancillary Response
    2.3  Implementation
    2.4  Rationale
    2.5  Reminders
3  THE HEASARC STANDARD RMF FORMAT
    3.1  The RMF Redistribution Extension
        3.1.1  Extension Header
        3.1.2  Data Format
        3.1.3  Points to Note & Conventions
    3.2  The RMF EBOUNDS Extension
        3.2.1  Extension Header
        3.2.2  Data Format
        3.2.3  Points to Note & Conventions
4  THE HEASARC STANDARD ARF FORMAT
    4.1  The ARF Extension
        4.1.1  Extension Header
        4.1.2  Data Format
        4.1.3  Points to Note & Conventions
5  USAGE: TYPICAL SCENARIOS
6  SPECIAL CASES
7  EXAMPLE FITS HEADERS
    7.1  ASCA RMF
        7.1.1  RSP_MATRIX Extension
        7.1.2  EBOUNDS Extension
    7.2  ASCA ARF
        7.2.1  SPECRESP Extension

1  INTRODUCTION

All calibration files within the High Energy Astrophysics Science Archive Research Center (HEASARC) will make use of the Flexible Image Transport System (FITS; eg see Wells et al. 1981, Griesen & Harten 1981), including all the recent enhancements of the original FITS formats. Specifically, wide use will be made of 'extensions' (Grosbol et al 1988), 'ASCII tables' (Harten et al 1988), and 'binary tables' (Cotton, Tody & Pence 1995).
Calibration files within the HEASARC Calibration Database (CALDB) have been classified into 2 types: An overview of the relationship between the BCFs, CPFs and other elements within the generic calibration dataflow is given in CAL/GEN/91-001 (George 1992).
This document describes in detail the format adopted by the HEASARC for the calibration files required during the spectral analysis of (PHA) data.

2  OVERVIEW

2.1  The Redistribution Matrix

X-ray spectral analysis consists of convolving a model spectrum with the response of the detection system, and comparison of this convolved model with the observed data in order to constrain the model parameters and thus derive physical quantities (like absorption columns, fluxes, emission measures, etc.) The "detector response" R(I,E) is proportional to the probability that an incoming photon of energy E will be detected in the output detector channel I. As such, the response is a continuous function of E, while the detector output consists of only a discrete number of channels. The continuous function is converted to a discrete function by creating a "response matrix" RD(I,J) at discrete energies EJ such that

RD(I,J)=

EJ

EJ−1 
R(I,E) dE

(EJ−EJ−1)
(1)
RD is often referred to as the "Redistribution Matrix", since it describes how a photon of energy EJ−1 < E < EJ is "redistributed" into output detector channels. The file which contains the "Redistribution Matrix" has been called the "Redistribution Matrix File", or RMF for short.

2.2  Detector Sensitivity, or Ancillary Response

In general the response of a detector to a source of photons depends not only on the redistribution of photons but also on the sensitivity of the detector to photons of known energy. For example, for many X-ray detectors, the sensitivity is a function of off-axis angle: a source observed on-axis usually appears brighter than the same source observed away from the detector optical axis. The sensitivity of a detector to a photon of a given energy EJ−1 < E < EJ can be described by an array of values A(J). The A(J) matrix is often called the "Ancillary Response Matrix", while the file which contains this matrix is usually called the Ancillary (sometimes, Auxiliary) Response File, or ARF for short. The Ancillary Response Matrix gives the "effective area" of the detector system, and usually includes such components as mirror vignetting, filters, etc.

2.3  Implementation

In the general case, spectral analysis of a PHA file (eg using XSPEC or equivalent Data Analysis Package) requires access to the following Calibration Product Files:
  1. A DETECTOR REDISTRIBUTION MATRIX FILE (RMF)
    • created by folding together individual components due to the:
      • Detector Gain
      • Detector Energy Resolution (including the response to a monoenergetic source   eg escape peaks, partial charge tail etc)
    • consisting of a compressed 2-d (energy vs PHA channel) FITS extension (Section 3).
    • and a second extension explicitly listing the nominal energy range of each PHA channel.
  2. AN ANCILLARY RESPONSE FILE (ARF)
    • containing the summed contribution of efficiency components, ie those not involved in the redistribution of photons such as the:
      • Effective Area of the Telescope/Collimator (including vignetting),
      • Filter Transmission (if any)
      • Detector Window Transmission
      • Detector Efficiency
      • any additional energy dependent effects
        (eg correction factors for the p.s.f.)
    • in a single 1-d (energy) FITS extension (Section 4).
However, though strongly discouraged, under certain circumstances, all the above calibration information may instead be incorporated into a single file (see Section 6).
It should be noted that the PHA channels used in all the i/p files to the spectral analysis package - ie within the RMF, ARF & PHA files - in all cases refer to raw detector channels. In the case of RMFs, the number of raw channels is given explicitly by the DETCHANS keyword within the MATRIX extension (see below). Any desired rebinning of the raw PHA data can be specified by the GROUPING flag within the PHA file (OGIP/92-007, Arnaud, George & Tennant 1992) The rebinning of the data is then performed within the spectral analysis package, along with appropriate rebinning of the calibration data supplied by the RMF & ARF.

2.4  Rationale

For many instruments, the Detector Gain & Energy Resolution do not vary significantly with detector coordinates or time (in particular not within an 'observation'). In such cases, a single RMF can be constructed for a given observation and used in conjunction with the spectral analysis of ALL the sources in the field-of-view. Each of the individual PHA files associated with each source will thus have its own customized ARF. The spectral analysis package will then read in the PHA/ARF pairs along with the common RMF. (Situations in which the use of a common RMF is not possible are discussed in Section 5.)
Furthermore, the isolation of those components which are not concerned with the redistribution process, and hence are a simple function of energy for a given PHA file (ie given time, Detector position, mode etc), into the ARF allows these components to be listed individually within the ARF if desired (see Section 4). It should be noted however that the product (Prod array below) of the components to the ARF will always be listed.

2.5  Reminders

`PI' channels (ie from a redistribution of the raw PHA channel data within a PHA file onto a scale appropriate for some `standard' Detector gain setting etc) should wherever possible NOT1 be used: the inclusion of the Detector gain within the RMF provides the necessary PHA channel → energy conversion.
In the case of (significant) gain changes during a given 'observation' (eg as often the case for the Einstein Observatory IPC) separate PHA & RMFs should be constructed prior to spectral analysis (and the PHAs analysed in conjunction with their respective ARFs & RMFs either alone or simultaneously).
An RMF contains only information applicable to the redistribution process. The Effective area, Filter (if appropriate) & Window Transmissions are folded into the ARF. Any additional effects such as obscuration by the Window Support Structure, absorption due to deposits (eg water ice) upon the the Window surface etc will also be folded into the ARF. Again this is in order to minimise the number of RMFs required for a given observation dataset (hopefully to one in many instances). Hence this provides a reduction in the requirements for disk-space, and facilitates any investigation Users may wish to perform into the effect on their spectral analysis of varying the contribution any such components.

3  THE HEASARC STANDARD RMF FORMAT

The standard RMF format consists of a FITS file with a null primary array and two extensions: both employing the BINTABLE FITS format.

3.1  The RMF Redistribution Extension

In order to minimize disk-space requirements, the RMF Redistribution Matrix will be in a compressed format in which all matrix elements below a given threshold (specified by the LO_THRES keyword below) are not stored. In fact the format is very similar to that used currently by the XSPEC *.rsp SF files.

3.1.1  Extension Header

The header must include the following (mandatory) keywords/values:
The following optional keywords may be useful for programs reading the file in that they specify the amount of memory various arrays will require.
The following optional keywords supply further information:
The following keywords are now obsolete but may be included for the benefit of old software. They should be commented as obsolete.
Finally, the following keywords are mandatory if these calibration data are ever to form an entry in a Calibration Index File (CIF; see CAL/GEN/92-008, George, Pence & Zellar 1992)
These keywords and their acceptable values are listed in more detail in CAL/GEN/92-011 (George, Zellar & Pence 1992)
However, it should be noted that there is often no such requirement for RMF or ARF files as they are usually specific to a given PHA file (but see Section 6).

3.1.2  Data Format

In the general case, the organization of the data within this extension will be as follows (with the matrix x-axis = raw PHA channel, y-axis = Energy) with each row of the BINTABLE referring to a single energy range (thus the number of rows = number of energy bins) and consist of the following columns:
  1. Elow, a 4-byte REAL scalar for each row containing the lower energy bound of the energy bin.
    The FITS column name is ENERG_LO.
    The recommended units are keV.
  2. Ehigh, a 4-byte REAL scalar for each row. containing the upper energy bound of the energy bin.
    The FITS column name is ENERG_HI.
    The recommended units are keV.
  3. Ngrp, a 2-byte INTEGER scalar for each row containing the number of 'channel subsets' for for the energy bin (see below).
    The FITS column name is N_GRP.
    (unitless).
  4. Fchan, a fixed- or variable-length 2-byte or 4-byte INTEGER array for each row. Contains the channel number of the start of each "channel subset" for the energy bin.
    The FITS column name is F_CHAN.
    (unitless).
  5. Nchan, a fixed- or variable-length 2-byte or 4-byte INTEGER vector for each row. Contains the number of channels within each "channel subset" for the energy bin.
    The FITS column name is N_CHAN.
    (unitless).
  6. Mat, a (fixed- or variable-length) REAL vector (array, each element within which is 4-byte) containing all the response values for each 'channel subset' for the energy bin.
    The FITS column name is MATRIX.
    (unitless).
These are summarized in Table 1.


Table 1: OGIP format (1992a) for storing photon redistribution matrices within an RMF



Extension
to (filename).RMF

Name: RMF
Description: Photon Redistribution Matrix
Format: BINTABLE
column
1 23 4 5 6
contents
Low energy High energyNumber First channel Number chans (non-zero)
bound bound of channelin each subset in each subset Matrix elements
for row for row subsets for row for row for row for row
Elow Ehigh Ngrp Fchan(i) Nchan(j) Mat(k)
i=1,Ngrpj=1,Ngrpk=1,∑j=1Ngrp Nchan(j)
format of each column
4-byte 4-byte 2-byte 2-byte or 4-byte 2-byte or 4-byte 4-byte
real real integer integer integer real
array array array
total number of elements per row
1 1 1 variable, or variable, or variable, or
MAX(Ngrp) MAX(Ngrp) MAX(∑j=1Ngrp Nchan(j))
column name
ENERG_LO ENERG_HI N_GRP F_CHAN N_CHAN MATRIX




























A final column may be added for responses of grating instruments.
  1. Order, a (fixed- or variable-length) INTEGER vector (array, each element within which is 2-byte) for each row containing the dispersion order of each 'channel subset' in the energy bin.
    The FITS column name is ORDER.
    (unitless).
This column matches the F_CHAN and N_CHAN columns and requires that every 'channel subset' be for a single order.

3.1.3  Points to Note & Conventions

3.2  The RMF EBOUNDS Extension

This extension lists the (nominal) energy boundaries of each of the (raw) detector channels within the redistribution matrix given above. (It should be stressed that these energies are Not the same as those given in the ENERG_LO & ENERG_HI columns of the MATRIX extension above.) This information is required by spectral analysis packages when (say) the results of spectral analysis (PHA data and best-fitting model) are required to be displayed as a function of photon energy, rather than detector channel. Since the number of raw channels in the matrix of many detectors is large, clearly a great saving in processing time during such spectral analysis tasks is offered if this information is provided explicitly by the RMF.
The format described here is relatively straightforward, being a simple 1-dimensional list (as a function of raw detector PHA channel) listing the appropriate energy boundaries.

3.2.1  Extension Header

For clarity, the header must include the same mandatory keywords as the RMF extension, namely: along with the optional keywords
The following keywords are now obsolete but may be included for the benefit of old software. They should be commented as obsolete.
Finally, if these calibration data are ever to form an entry in a Calibration Index File, the mandatory C*** keywords listed in Section 3.1.1 are also mandatory, but in this case with CCNM0001 = 'EBOUNDS'.

3.2.2  Data Format

A BINTABLE FITS format has been chosen whereby each each row refers to a single detector channel. The number of rows is thus the number of (raw) detector channels and must correspond exactly to the channels within the PHA file and hence also to the value of the DETCHANS keyword in the RMF MATRIX extension described above. Thus, we have
  1. Chan, a 2-byte or 4-byte INTEGER scalar giving the raw channel number for each row.
    The FITS column name is CHANNEL.
    (unitless)
  2. Emin, a 4-byte REAL scalar for each for each row containing the nominal energy corresponding to the lower boundary of the detector channel.
    The FITS column name is E_MIN.
    The recommended units are keV.
  3. Emax, a 4-byte REAL scalar for each for each row containing the nominal energy corresponding to the upper boundary of the detector channel.
    The FITS column name is E_MAX.
    The recommended units are keV.
Table 2 summarizes the organisation of this extension


Table 2: OGIP format (1992a) for the EBOUNDS extension within RMFs



Extension
to (filename).RMF

Name: EBOUNDS
Description: Nominal energy boundaries for each detector channel
Format: BINTABLE
column
1 23
contents
Detector Low energy High energy
channel bound bound
number for row for row
Chan Emin Emax
format of each column
2-byte or 4-byte 4-byte 4-byte
integer real real
total number of elements per row
1 1 1
column name
CHANNEL E_MIN E_MAX




























3.2.3  Points to Note & Conventions

4  THE HEASARC STANDARD ARF FORMAT

The ARFs are relatively straightforward, consisting of a simple 1-dimensional list (as a function of energy) of the product of the various components required for spectral analysis not involved in the photon redistribution process (see Section 2.4).

4.1  The ARF Extension

4.1.1  Extension Header

The header must include the following (mandatory) keywords:
The following optional keywords supply further information:
The following keywords are now obsolete but may be included for the benefit of old software. They should be commented as obsolete.
As for the RMF file, if these calibration data are ever to form an entry in a Calibration Index File, the C*** keywords listed in Section 3.1.1 are also mandatory, but in this case with CCNM0001 = 'SPECRESP'. Furthermore however, if (in addition to the Prod array) the ARF SPECRESP extension also lists each of individual contributing components (see below), and these components are too be be listed in the Index File, then each component must have its own unique set of C*** keywords (denoted by CCNMXXXX etc where XXXX is a number of the form 0002, 0003 etc In this case, the CCNMXXXX must conform to the appropriate standards given in CAL/GEN/92-011 (George, Zellar & Pence 1992).

4.1.2  Data Format

The general HEASARC standard for ARFs also makes use of the BINTABLE FITS format, and thus the data again resides in a single extension of a FITS file (though generally NOT the RMF) with a null primary array. As in the case of the RMFs, each row of the BINTABLE refers to a single energy range. The number of rows hence equals the number of energy bins and must directly correspond to those in the corresponding RMF. In all cases the following columns are included (preferably as the first 3 columns within the table):
  1. Elow, a 4-byte REAL scalar for each row containing the lower energy bound of the energy bin.
    The FITS column name is ENERG_LO.
    The recommended units are keV.
  2. Ehigh, a 4-byte REAL scalar for each row containing the upper energy bound of the energy bin.
    The FITS column name is ENERG_HI.
    The recommended units are keV.
  3. Prod, a 4-byte REAL scalar for each row containing the product of all the components (effective area, filter transmission, correction factors etc) specific to a given PHA file (ie the spectral response of the instrument as a whole).
    The FITS column name is SPECRESP.
    The recommended units are cm2.
Other columns can be added to show the various components out of which Prod was constructed but these are optional.
Table 3 summarizes the organisation of an ARF.


Table 3: OGIP format (1992a) for ARFs



Extension
to (filename).ARF

Name: ARF
Description: Ancillary Response File
Format: BINTABLE
column
1 23 4, 5, 6 ... (as necessary)
contents
Low energy High energyProduct of Component 1, Component 2, Component 3, ...
bound bound componentsfor row
for row for row for row (as necessary)
Elow Ehigh Prod C1,    C2,    C3, ...
format of each column
4-byte 4-byte 4-byte 4-byte
real real real real (or 2-byte integer if more appropriate)
total number of elements per row
1 1 1 1,    1,    1, ...
column name
ENERG_LO ENERG_HI SPECRESP (as in original BCF file)




























4.1.3  Points to Note & Conventions

5  USAGE: TYPICAL SCENARIOS

For non-imaging devices (with a time-stable Detector Gain etc) a User extracts a PHA file, runs a response generator and constructs a RMF & ARF. These are read into their favourite Data Analysis Package (eg XSPEC) along with the PHA file, and spectral analysis attempted. Should the User then wish to investigate the effect of alternate calibrations, a response generator can be run again/spawned. The User then specifies the desired calibration, and a new ARF written. Spectral analysis could continue using the original PHA file & RMF in conjunction with the new ARF. In some cases a single RMF may be applicable to several contiguous observational datasets within the HEASARC archive.
For imaging instruments (with a time- and position-stable Detector Gain etc) a User performs an almost identical set of actions as above for each PHA file extracted (ie from each source in the image). Each PHA file therefore has an associated ARF file, which the User creates and/or customizes using a response generator. However all the PHA files share a single RMF.
For imaging instruments (with a time-stable Detector Gain etc, but which varies with detector position) a User has to construct both a RMF & ARF for each PHA file extracted (ie from each source in the image). Users will obviously be able to customize the individual ARFs as desired.
For instruments (of any type) for which the Detector Gain etc is not stable with time (ie significantly varies over the course of a pointing), the observational dataset should be broken-down into a series of periods for which all Detector-related quantities are considered sufficiently time-stable. Separate PHA files, RMFs and associated ARFs can then be constructed for each of these periods (with each RMF obviously containing the matrix constructed using the gain setting appropriate to its time-window). Spectral analysis is then performed on these files either individually or simultaneously.

6  SPECIAL CASES

It should be stressed that the spectral response matrix of instruments for which either: can (and should) be written adopting the RMF format described above.
If no ARF is specified within the PHA file (via the ANCRFILE keyword - see OGIP/92-007 (Arnaud, George & Tennant 1992),
then the Spectral Analysis Package should assume that the instrument spectral response (i.e. the Prod array from Table 3) has been folded in with the redistribution matrix (Mat from Table 1), and this information is what is stored in the RMF extension. In this case the following changes to the list of mandatory keywords/values given in Section 3.1.1 are necessary to the header of the (new) RMF extension:
Again, it is emphasized that this is generally not recommended, especially in the case of future missions.

7  EXAMPLE FITS HEADERS

As an example, below we list the relevant keywords from an ASCA SIS0 RMF and ARF.

7.1  ASCA RMF

7.1.1  RSP_MATRIX Extension

XTENSION= 'BINTABLE'           / binary table extension
BITPIX  =                    8 / 8-bit bytes
NAXIS   =                    2 / 2-dimensional binary table
NAXIS1  =                   34 / width of table in bytes
NAXIS2  =                 1180 / number of rows in table
PCOUNT  =              1031160 / Number of bytes acumulated in heap
GCOUNT  =                    1 / one data group (required keyword)
TFIELDS =                    6 / number of fields in each row
TTYPE1  = 'ENERG_LO'           / label for field   1
TFORM1  = 'E       '           / data format of field: 4-byte REAL
TUNIT1  = 'keV     '           / physical unit of field
TTYPE2  = 'ENERG_HI'           / label for field   2
TFORM2  = 'E       '           / data format of field: 4-byte REAL
TUNIT2  = 'keV     '           / physical unit of field
TTYPE3  = 'N_GRP   '           / label for field   3
TFORM3  = 'I       '           / data format of field: 2-byte INTEGER
TTYPE4  = 'F_CHAN  '           / label for field   4
TFORM4  = 'PI(2)   '           / data format of field: variable length array
TTYPE5  = 'N_CHAN  '           / label for field   5
TFORM5  = 'PI(2)   '           / data format of field: variable length array
TTYPE6  = 'MATRIX  '           / label for field   6
TFORM6  = 'PE(418) '           / data format of field: variable length array
EXTNAME = 'MATRIX  '           / name of this binary table extension
TLMIN4  =                    0 / First legal channel number
TLMAX4  =                  511 / Highest legal channel number
TELESCOP= 'ASCA    '           / mission/satellite name
INSTRUME= 'SIS0    '           / instrument/detector
FILTER  = 'NONE    '           / filter information
CHANTYPE= 'PI      '           / Type of channels (PHA, PI etc)
DETCHANS=                  512 / Total number of detector PHA channels
LO_THRES=             1.00E-07 / Lower probability density threshold for matrix
HDUCLASS= 'OGIP              ' / Keyword information for Caltools Software.
HDUCLAS1= 'RESPONSE          ' / Keyword information for Caltools Software.
HDUCLAS2= 'RSP_MATRIX        ' / Keyword information for Caltools Software.
HDUVERS = '1.3.0             ' / Keyword information for Caltools Software.
HDUCLAS3= 'DETECTOR          ' / Keyword information for Caltools Software.
CCNM0001= 'MATRIX            ' / Keyword information for Caltools Software.
CCLS0001= 'CPF               ' / Keyword information for Caltools Software.
CDTP0001= 'DATA              ' / Keyword information for Caltools Software.
CVSD0001= '1993-02-20        ' / Keyword information for Caltools Software.
CVST0001= '11/11/11          ' / Keyword information for Caltools Software.
CDES0001= 'SISRMGv1.10:1180x512 S0C0 G"0234"  V100 P40 E1.6                    '
CBD10001= 'CHAN(0- 511)      ' / Keyword information for Caltools Software.
CBD20001= 'ENER(0.2-12.0)keV'  / Keyword information for Caltools Software.
CBD30001= 'GRADE("0234" )         ' / Keyword information for Caltools Software.
CBD40001= 'RAWX(-95- 325)     ' / Keyword information for Caltools Software.
CBD50001= 'RAWY( 22- 444)     ' / Keyword information for Caltools Software.
RMFVERSN= '1992a   '           / Obsolete
HDUVERS1= '1.0.0             ' / Obsolete
HDUVERS2= '1.2.0             ' / Obsolete
END

7.1.2  EBOUNDS Extension

XTENSION= 'BINTABLE'           / binary table extension
BITPIX  =                    8 / 8-bit bytes
NAXIS   =                    2 / 2-dimensional binary table
NAXIS1  =                   10 / width of table in bytes
NAXIS2  =                  512 / number of rows in table
PCOUNT  =                    0 / size of special data area
GCOUNT  =                    1 / one data group (required keyword)
TFIELDS =                    3 / number of fields in each row
TTYPE1  = 'CHANNEL '           / label for field   1
TFORM1  = 'I       '           / data format of field: 2-byte INTEGER
TUNIT1  = 'channel '           / physical unit of field
TTYPE2  = 'E_MIN   '           / label for field   2
TFORM2  = 'E       '           / data format of field: 4-byte REAL
TUNIT2  = 'keV     '           / physical unit of field
TTYPE3  = 'E_MAX   '           / label for field   3
TFORM3  = 'E       '           / data format of field: 4-byte REAL
TUNIT3  = 'keV     '           / physical unit of field
EXTNAME = 'EBOUNDS '           / name of this binary table extension
TLMIN1  =                    0 / First legal channel number
TLMAX1  =                  511 / Highest legal channel number
TELESCOP= 'ASCA    '           / mission/satellite name
INSTRUME= 'SIS0    '           / instrument/detector
FILTER  = 'NONE    '           / filter information
CHANTYPE= 'PI      '           / Type of channels (PHA, PI etc)
DETCHANS=                  512 / Total number of detector PHA channels
SMOOTHED=                    0 / 0 = raw, 1-12 = smooth, -1 = ep-lin, -2 = mean-
HDUCLASS= 'OGIP              ' / Keyword information for Caltools Software.
HDUCLAS1= 'RESPONSE          ' / Keyword information for Caltools Software.
HDUCLAS2= 'EBOUNDS           ' / Keyword information for Caltools Software.
HDUVERS = '1.2.0             ' / Keyword information for Caltools Software.
CCNM0001= 'EBOUNDS           ' / Keyword information for Caltools Software.
CCLS0001= 'CPF               ' / Keyword information for Caltools Software.
CDTP0001= 'DATA              ' / Keyword information for Caltools Software.
CVSD0001= '1993-02-20        ' / Keyword information for Caltools Software.
CVST0001= '11/11/11          ' / Keyword information for Caltools Software.
CDES0001= 'SISRMGv1.10:1180x512 S0C0 G"0234"  V100 P40 E1.6                  '
CBD10001= 'CHAN(0- 511)      ' / Keyword information for Caltools Software.
CBD20001= 'ENER(0.2-12.0)keV'  / Keyword information for Caltools Software.
CBD30001= 'GRADE("0234" )         ' / Keyword information for Caltools Software.
CBD40001= 'RAWX(-95- 325)     ' / Keyword information for Caltools Software.
CBD50001= 'RAWY( 22- 444)     ' / Keyword information for Caltools Software.
RMFVERSN= '1992a   '            / Obsolete
HDUVERS1= '1.0.0              ' / Obsolete
HDUVERS2= '1.2.0              ' / Obsolete
END

7.2  ASCA ARF

7.2.1  SPECRESP Extension

XTENSION= 'BINTABLE'           / binary table extension
BITPIX  =                    8 / 8-bit bytes
NAXIS   =                    2 / 2-dimensional binary table
NAXIS1  =                   12 / width of table in bytes
NAXIS2  =                 1180 / number of rows in table
PCOUNT  =                    0 / size of special data area
GCOUNT  =                    1 / one data group (required keyword)
TFIELDS =                    3 / number of fields in each row
TTYPE1  = 'ENERG_LO'           / label for field   1
TFORM1  = '1E      '           / data format of field: 4-byte REAL
TUNIT1  = 'keV     '           / physical unit of field
TTYPE2  = 'ENERG_HI'           / label for field   2
TFORM2  = '1E      '           / data format of field: 4-byte REAL
TUNIT2  = 'keV     '           / physical unit of field
TTYPE3  = 'SPECRESP'           / label for field   3
TFORM3  = '1E      '           / data format of field: 4-byte REAL
TUNIT3  = 'cm**2   '           / physical unit of field
EXTNAME = 'SPECRESP'           / name of this binary table extension
TELESCOP= 'ASCA    '           / Telescope (mission) name
INSTRUME= 'SIS0    '           / Instrument name
FILTER  = 'NONE    '           / Instrument filter
HDUCLASS= 'OGIP    '           / Organisation devising file format
HDUCLAS1= 'RESPONSE'           / File relates to response of instrument
HDUCLAS2= 'SPECRESP'           / effective area data is stored
HDUVERS = '1.1.0   '           / Version of file format
RESPFILE= 'test.rmf'           / RMF file used to get the energies
WAOAA   =          7.68984E+00 / WMAP-wgtd avg off-axis ang
HISTORY   ARF created by ascaarf v3.00
HISTORY   from test.sp
HISTORY   using test.rmf
HISTORY   with extended source algorithm
HISTORY   XRT effec area from /FTP/caldb/data/asca/xrt/bcf/xrt_ea_v2_0.fits
HISTORY       PSF from        /FTP/caldb/data/asca/xrt/bcf/xrt_psf_v2_0.fits
HISTORY    Input WMAP array has size   28 by   28 bins
HISTORY                  expanded to   28 by   28 bins
HISTORY    First WMAP bin is at detector pixel  336  648
HISTORY      8 detector pixels per WMAP bin
HISTORY    WMAP bin size is   0.21600 mm
HISTORY                       0.21216 arcmin
HISTORY    Selected region size is   1.8701     arcmin^2
HISTORY    Optical axis is detector pixel 662.72 559.02
HISTORY    1180 energies from RMF file
HISTORY    Effective area fudge applied
HISTORY    Arf filter applied
ARFVERSN= '1992a   '           / Obsolete
HDUVERS1= '1.0.0   '           / Obsolete
HDUVERS2= '1.1.0   '           / Obsolete
END

ACKNOWLEDGMENTS

We thank the numerous people, both inside and outside the OGIP, who have contributed ideas and suggestions. In particular we thank Alan Smale and Mike Corcoran.

REFERENCES

Information regarding on-line versions of any of the following references with an OGIP Memo number (ie documents starting OGIP/.. or CAL/..) can most easily be found via the WorldWide Web by following the links from the URL:
http://heasarc.gsfc.nasa.gov/docs/heasarc/caldb/caldb_doc.html
Most OGIP Calibration Memos of general community interest will eventually appear as articles in Legacy, but are also available on request from The Office of Guest Investigator Programs, Code 660.2, NASA/GSFC, Greenbelt, MD 20771, USA.
Arnaud, K.A., George, I.M. & Tennant, A., 1992.
(OGIP/92-007)
Cotton, W.D., Tody, D. & Pence, W.D. 1995. Astron. Astrophys. Suppl., 113,159.
George, I.M., 1992. Legacy, 1, 56.
(CAL/GEN/91-001)
George, I.M., Pence, W. & Zellar, R. 1992.
(CAL/GEN/92-008)
George, I.M., Zellar, R. & Pence, W., 1992.
(CAL/GEN/92-011)
George, I.M., Arnaud, K.A. & Ruamsuwan, L., 1992.
(CAL/SW/92-004)
Griesen, E.W. & Harten, R.H., 1981. Astron. Astrophys. Suppl., 44, 371.
Grosbol, P., Harten, R.H., Greisen, E.W. & Wells, D.C., 1988. Astron. Astrophys. Suppl., 73,365.
Pence, W., 1992. Legacy, 1, 14..
Wells, D.C., Griesen, E.W. & Harten, R.H., 1981, Astron. Astrophys. Suppl., 44, 363.

USEFUL LINKS TO OTHER HTML PAGES

The following useful links are available (in the HTML version of this document only):

Footnotes:

1A primary goal of the HEASARC is to standardize the format of similar files from different instruments. Besides strictly being the incorrect method in the general case, the mapping of the PHA data from the observed to some 'standard' channel grid cannot be performed correctly for low resolution detectors.
However, in the case of certain past and present missions, unfortunately the use of PI channels may be unavoidable since the necessary information (ie to construct & use BCFs) has been lost or is unavailable from the h/w team. However, in such cases, the data describing the entire instrument response should be stored in the same format as the RMFs described below, (see also Section 6).
PHA datasets in which use a PI channel grid are denoted by the CHANTYPE = 'PI' keyword within the PHA file (see OGIP/92-007, Arnaud, George & Tennant 1992)
2A variable-length FITS array requires at least 12 bytes of disk storage space: 4 bytes for the length of the vector, 4 bytes for the offset address, and 4 bytes for the value of each element. Thus using variable-length format for an array will lead to a saving of disk-space only if the maximum number of elements in that array is greater than 3.
3Due to always having to read the offset value first, before reading the value of a given element within the array, there is a significant performance inefficiency in using variable-length vectors.
4This is denoted by the CHANTYPE = 'PI' keyword within the PHA file (see OGIP/92-007, Arnaud, George & Tennant 1992).
Examples include the current versions of the ROSAT PSPC and Einstein Observatory IPC datasets within the HEASARC archive


File translated from TEX by TTHgold, version 4.00.
On 7 Dec 2011, 15:07.