INTEGRAL/SPI Analysis With
XSPEC Version 12+
(Excerpted from the XSPEC 12
Users Manuel)
1. Overview
The
INTEGRAL Spectrometer (SPI) is a coded-mask telescope, with a
19-element Germanium detector array. The Spectral resolution is ~500, and the
angular resolution is ~3°. Unlike focusing
instruments however, the detected photons are not directionally tagged, and a
statistical analysis procedure, using for example cross-correlation techniques,
must be employed to reconstruct an image. The description of the XSPEC analysis
approach[1]
which follows assumes that an image reconstruction has already been performed;
see the SPIROS utility within the INTEGRAL offline software analysis package (OSA), OR, the positions on the sky of all sources to be
analyzed are already known (which is often the case). Those unfamiliar with INTEGRAL data analysis
should refer to the OSA documentation. Thus, the INTEGRAL/SPI
analysis chain must be run up to the event binning level (if the FoV source content is known, e.g. from published catalogs,
or from IBIS image analysis), or the image reconstruction level. SPIHIST should
be run selecting the "PHA" output option, and selecting detectors
0-18. This will produce and OGIP standard type-II PHA spectral file, which contains
multiple, detector count spectra. In
addition, the SPIARF procedure should be run once for each source to be
analyzed, plus one additional time to produce a special response for analysis
of the instrumental background (more on this shortly). If this is done
correctly, and in the proper sequence, SPIARF will create a table in the PHA-II
spectral file, which will associate each spectrum with the appropriate set of
response matrices. The response matrices are then automatically loaded into
XSPEC upon execution of the "data" command in a manner very
transparent to the user. You will also need to run SPIRMF (unless you have
opted to use the default energy bins of the template SPI RMFs).
Finally, you will need to run the FTOOL SPIBKG_INIT. Each of these utilities -
SPIHIST, SPIARF, SPIRMF and SPIBKG_INIT - are documented elsewhere, either in
the INTEGRAL or (for SPIBKG_INIT) the LHEASOFT/FTOOLS software documentation.
There
are several complications regarding the spectral de-convolution of
coded-aperture data. One already mentioned is the source confusion issue; there
may be multiple sources in the FoV, which are lead to
different degrees of shadowing on different detectors. Thus, a separate
instrumental response must be applied to a spectral model for each possible
source, for each detector. This is further compounded by the fact that INTEGRAL's typical mode of observation is
"dithering". A single observation may consist of ~10's of individual
exposures at raster points separated by ~2°. This further enumerates
the number of individual response matrices required for the analysis. If there
are multiple sources in the FoV, then additional
spectral models can be applied to an additional set of response matrices,
enumerated as before over detector and dither pointing. This capability - to
model more than one source at a time in a given Chi-Square (or alternative)
minimization procedure - did not exist in previous versions of XSPEC.
Mathematically, the full de-convolution problem is to minimize:
where:
run over
instrument pointings and detectors;
I runs over individual detector channels
j enumerates
the sources detected in the field at different position 
E indexes the energies in the source model
xs parameters
of the source model, which is combined with the response
xb parameters
of the background model, expressed as a function of detector channel
Here, d, p, I indicate summations over detector, dither
pointing, and spectral energy channel, E indicates summation over the photon
model energy bins, j :(q ,j)
specify source directions and the xs's / xb's are
the set of source/background model parameters. Examination of this equation
reveals one more complication; the term B represents the background, which, unlike
for chopping, scanning or imaging experiments, must be solved for
simultaneously with the desired source content. The proportion of
background-to-source counts for a bright source such as the Crab is ~1%.
Furthermore, the background varies as a function of detector, and time
(dither-points), making simple subtraction implausible. Thus, a model of the
background is applied to a special response matrix, and included in the
de-convolution algorithm.
Another
manner in which XSPEC analysis of INTEGRAL/SPI data is very different from
other instruments is the manner in which the response matrices are handled.
Since there are a large number of responses involved in the de-convolution
problem, memory use becomes a concern. To serially load the of the required
response matrices (as XSPEC normally does), would require ~(Nch)2´Np´Nd floating-point memory
locations per source. This could become quite large for high-spectral
resolution and/or long observation scenarios. To address this problem, a
methodology has been developed to reconstruct the required 2-D response
matrices from a basis set, consisting of a small number (3) of 2-D objects
(template RMFs), and a larger number of 1-D objects
(component ARFs). These comprise the output of SPIARF
and SPIRMF. The full matrices can then be reconstructed "on the fly"
at the minimization step of the calculation, and discarded after each use.
This, in principle, occurs all very transparently to the user.
2. Simple Analysis Example
We
now describe the step-by-step procedures for actual analysis examples. First, consider
an observation of the Crab, for which a (standard) 5°´5°dithering observation strategy was employed.
Since the Crab (pulsar and nebular components are of course un-resolvable at INTEGRAL's spatial resolution) is by far the brightest
source in it immediate region of the sky, and its position is precisely known,
we can opt not to perform SPI or IBIS imaging analysis prior to XSPEC analysis.
We thus run the standard INTEGRAL/SPI
analysis chain on detectors 0-18 up to the SPIHIST level for (or BIN_I level in the terminology
of the INTEGRAL documentation), selecting the "PHA" output option. We
then run SPIARF, providing the name of the PHA-II file just created, and selecting the "update" option in
the spiarf.par parameter file (you should refer to
the SPIARF documentation prior to this step if it is unfamiliar). The celestial
coordinates for the Crab are provided in decimal degrees (RA,Dec
= 83.63,22.01) interactively or by editing the parameter file. This may take a
few minutes, depending on the speed of your computer and the length of your
observation. Once completed, SPIARF must be run one more time, setting the
"bkg_resp" option to "y"; this
creates the response matrices to be applied to the background model, and
updates the PHA-II response database table accordingly. Then SPIRMF, which
interpolates the template RMFs to the users desired
spectral binning, also writes information to the PHA response database table to
be used by XSPEC. Finally, you should run SPIBKG_INIT, which will construct a
set of bbackground spectral templates to initialize
the SPI background model currently installed in XSPEC (read the FTOOLS help for
that utility carefully your first time). Your now ready to run XSPEC; a sample
session might look like this (some repetitive output has been suppressed):
%
% xspec
XSPEC version: 12.0.10alpha
Build Date/Time: Thu Oct 2
XSPEC>package
require Integral 1.0
1.0
XSPEC>data
./myDataDir/rev0044_crab.pha{1-19}
19
spectra in use
RMF
# 1
Using Response (RMF) File resp/comp1_100x100.rmf
RMF
# 2
Using Response (RMF) File resp/comp2_100x100.rmf
RMF
# 3
Using Response (RMF) File resp/comp3_100x100.rmf
Using
Multiple Sources
For
Source # 1
Using Auxiliary Response (ARF) Files
resp/rev0044_100ch_crab_cmp1.arf.fits
resp/rev0044_100ch_crab_cmp2.arf.fits
resp/rev0044_100ch_crab_cmp3.arf.fits
For
Source # 2
Using Auxiliary Response (ARF) Files
resp/rev0044_100ch_bkg_cmp1.arf.fits
resp/rev0044_100ch_bkg_cmp2.arf.fits
resp/rev0044_100ch_bkg_cmp3.arf.fits
Source
File: ./myDataDir/rev0044_crab.pha{1}
Net
count rate (cts/s) for Spectrum No. 1 3.7011e+01
+/- 1.2119e-01
Assigned to Data Group No. : 1
Assigned to Plot Group No. : 1
Source
File: ./myDataDir/rev0044_crab.pha{2}
Net
count rate (cts/s) for Spectrum No. 2 3.7309e+01
+/- 1.2167e-01
Assigned to Data Group No. : 1
Assigned to Plot Group No. : 2
...
Source
File: ./myDataDir/rev0044_crab.pha{19}
Net
count rate (cts/s) for Spectrum No. 19 3.6913e+01
+/- 1.2103e-01
Assigned to Data Group No. : 1
Assigned to Plot Group No. : 19
XSPEC>mo
1:crab po
Input
parameter value, delta, min, bot, top, and max values for ...
1 PhoIndex
1.0000E+00 1.0000E-02 -3.0000E+00
-2.0000E+00 9.0000E+00 1.0000E+01
crab::powerlaw:PhoIndex>2.11 0.01 1.5 1.6 2.5 2.6
2
norm 1.0000E+00 1.0000E-02 0.0000E+00 0.0000E+00 1.0000E+24 1.0000E+24
crab::powerlaw:norm>8. 0.1 1. 2. 18. 20.
…
XSPEC>mo 2:bkg spibkg5
Input
parameter value, delta, min, bot, top, and max values for ...
1
Par_1 0.0000E+00 1.0000E-02 -2.0000E-01 -1.5000E-01 1.5000E-01 2.0000E-01
bkg::spibkg5:Par_1>/*
…
_____________________________________________________________________________________________________
XSPEC>ign
1-19:68-80
...
XSPEC>ign
1-19:90-100
...
XSPEC>fit
Number
of trials and critical delta: 10
1.0000000E-02
...
========================================================================
Model
bkg:spibkg5 Source No.: 2 Active/On
Model
Component Name: spibkg5 Number:
1
N
Name Unit Value Sigma
1
Par_1 9.0650E-03 +/- 2.8651E-03
2
Par_2 1.6174E-02 +/-
3.4778E-03
…
25
Par_25
-1.9537E-02 +/- 6.1429E-03
26
norm 9.7286E-01 +/-
1.3527E-03
________________________________________________________________________
========================================================================
Model
crab:powerlaw Source No.: 1 Active/On
Model
Component Name: powerlaw Number:
1
N
Name Unit Value Sigma
1 PhoIndex
2.1163E+00 +/- 1.8946E-02
2
norm 1.1390E+01 +/-
8.1414E-01
________________________________________________________________________
Chi-Squared =
1.8993005E+03 using 1463 PHA bins.
Reduced chi-squared = 1.3235544E+00 for 1435 degrees of freedom
Null hypothesis probability = 1.5268098E-15
XSPEC>
Note
that the syntax used for the data statement (appended curly bracket, specifying
use of spectra 1-19), and the separate model commands, which are indexed and
named (in this case simply "crab" for the source of interest and
"bkg" for the background model, "spibkg_lo". These commands are described in detail
elsewhere in this document, as are the the spibkg_lo, spibkg_med and spibkg_hi models. In this case, 100 logarithmically-spaced
energy bins spanning the nominal 20-8000 keV band of
the SPI instrument were used.
In
this example, only one dither-point was used to solve for the Crab spectrum,
and the background. The simple assumption of a single background spectrum (i.e.
no detector-to-detector variations) was assumed. In general, and particularly
for fainter sources, a much larger number of spectra will be needed for a
solution (and even for the Crab, the quality of the fit, and the accuracy of
the inferred parameters can be improved). Also, detector-to-detector and/or
time (i.e. pointing-to-pointing) variations will need to be considered. This
can be accomplished using the data-grouping feature of XSPEC, which will be
described subsequently. Also notice that channels between about 70 and 80 were
ignored; this is because there are detector electronic effects contaminating
the single-event data for energies from ~1250-1400 keV
(refer to the SPI data analysis manual for additional
discussion), and that there are a lot of (scientifically uninteresting)
background model parameters. Also, the highest energies were ignored, since the
source flux becomes insignificant relative to the background.
Some
results are illustrated below. These plots were generated with the sequence of
commands:
XPSEC>
setplot group 1-19
XSPEC>
plot ldata res
…
XSPEC> plot ufspec
Note
that without the "setplot group" command,
XSPEC would plot 19 sets of spectral data, models and residuals. The can become
confusing, especially as the number of spectra included in an analysis becomes
much larger than 19! On the other hand, it can be useful to divide the data
into subsets for plotting purposes, e.g. setplot
group 1-6 7-12 13-19, to get an idea of relative shadowing effects of the
coded-mask. The left hand plot illustrates the source model, the background
model, the total model (i.e. source + background), and the data (here in count
rates per channel). The right hand plot illustrates the "unfolded
model" (blue, power-law curve), the summed model, and the data as a photon
flux. A possible source of confusion is the similarity of the background model
curves plotted in theses two separate representations. The explanation is that
the background, which is dominated by instrumental contributions, is modeled in
detector count space (i.e. the background response matrix has unit effective
area. Thus, to be strictly correct, the right-hand plot is a hybrid of the
photon source model and the detector-rate background model. We further note
that at the present time, XSPEC does not have the capability to plot (or store
and manipulate) the background subtracted data. This is a feature under
consideration for a future release.
If
we had chosen a observation containing more than a single source, the procedure
would have been similar, except that the sequence of model commands would be
extended, e.g.
XSPEC>data ./MyDataDir/GCDE_aug_03.pha{1-475}
…
XSPEC>
model 1:1e1740 po
…
XSPEC>
model 2:gx1_4 po
…
XSPEC>
model 3:bkg spibkg_lo
…
Here
data from the
In
this case, the simple approach of applying constant background (i.e. no
detector-to-detector or pointing-to-pointing variation) to the full data set is
likely to be a poor approximation. A more realistic approach would be to use
the XSPEC grouping capability to handle such variations in the background
solution. This can be accomplished in the usual manner (refer to the
description of the grouping command in this document), however, it can become
tedious in terms of the required command line inputs. For example, to establish
a separate data group for each detector for a long (e.g. 5´5 dither) observations, a sequence of
commands such as this would be required:
XSPEC>
data 1:1 ./MyDataDir/rev0044_Crab.pha.fits{1}
XSPEC>
data 2:2 ./MyDataDir/rev0044_Crab.pha.fits{2}
XSPEC>
data 3:3 ./MyDataDir/rev0044_Crab.pha.fits{3}
...
XSPEC>
data
XSPEC>
data
XSPEC>
data
XSPEC>
data
...
XSPEC>
data
XSPEC>
data
XSPEC>
data
XSPEC>
data
...
XSPEC>
data 18:474 ./MyDataDir/rev0044_Crab.pha.fits{474}
XSPEC>
data 19:475 ./MyDataDir/rev0044_Crab.pha.fits{475}
One
might then for example, make a first cut attempt by fitting a constant
background. Then, as a next step, one might allow the normalization terms of
the background model to vary over the groups (i.e. over the detector plane).
This is accomplished with the "untie" command, using the following
sequence:
XSPEC> untie
bkg:52
XSPEC> untie
bkg:78
XSPEC> untie
bkg:104
XSPEC> untie
bkg:130
XSPEC> untie
bkg:156
XSPEC> untie
bkg:182
XSPEC> untie
bkg:208
XSPEC> untie
bkg:234
XSPEC> untie
bkg:260
XSPEC> untie
bkg:286
XSPEC> untie
bkg:312
XSPEC> untie
bkg:338
XSPEC> untie
bkg:364
XSPEC> untie
bkg:390
XSPEC> untie
bkg:416
XSPEC> untie bkg:442
XSPEC> untie
bkg:468
XSPEC> untie
bkg:487
Note
that use of the "bkg" identifier, which
associates the parameters index with the background model. The specific
sequence of numbers use here requires some explanation; the particular
background model employed has 25 parameters (which simply correspond in rank
order to the 25 most variable individual bins), and a normalization term, i.e.
parameter 26. Thus, the normalization for the second detector group is
parameter 52, for the third parameter 78, and so on. Similar command sequences
can be used to untie additional background model parameters. Supposing that we
did this and refitted the data. We then might, for example wish to go back and
freeze the individual normalization terms with the freeze command:
XSPEC> freeze
bkg:26
XSPEC> freeze
bkg:52
…
XSPEC> freeze
bkg:487
By
now though, you probably get the idea that this all requires an unreasonable
amount of command-line input. To circumvent this problem, a number of
INTEGRAL/SPI specific "tcl" scripts are
available which greatly streamline this process.
3. INTEGRAL Specific Command Line Scripts
3 .1 SPIdata
The
SPIdata procedure, which when installed can be
treated as an XSPEC command, greatly facilitates the data initialization step.
For example, the command
XSPEC> SPIdata ./MyData/Dir/rev0044_crab.pha 475 det Y
Opens
the Crab observation spectral data file, reads the 475 spectra into memory,
grouping them by detector. The "Y" then indicates that, yes, I wish to ignore the spectral data channels
corresponding to the known detector-electronic noise contamination (this is the
default). Instead of "det" as the grouping
option I could have selected "time" to group by time (quantized into
dither-pointing intervals). A "-" lead to the data being initialzed into a single group. The command:
XSPEC> SPIdata ./MyData/Dir/rev0044_crab.pha 475
Reads
the 475 spectra into a single data group, and ignores the undesirable channels.
If you forget all this, the command
XSPEC> SPIdata -h
will
remind you. The scripts SPIuntie, and SPIfreeze have
similar command-line syntax.
3.2 SPIuntie and SPIfreeze
XSPEC> SPIuntie bkg 475 19 -1
The
SPIuntie command script will accomplish the same
result as the sequence of "untie" commands in the INTEGRAL/SPI example
presented in this document. In that
case, we had loaded 475 spectra associated with a single 5´5-dither pattern centered on the Crab nebula.
The spectra were grouped by detector, which
is a common approach to SPI analysis given the known detector-to-detector
variations in the background rates. Suppose after an initial fitting pass, for
which we assumed a single background spectrum, we know wish to untie the
individual data group (i.e. detector) background models. This can be accomplished
by issuing 25 "untie" commands as previously noted, or in a single
command line using the SPIuntie command:
XSPEC>
SPIuntie bkg 475 19 -1
untie
bkg:52
Chi-Squared =
1.2030200E+04 using 1615 PHA bins.
Reduced chi-squared = 7.5852458E+00 for 1586 degrees of freedom
Null hypothesis probability = 0.0000000E+00
untie bkg:78
Chi-Squared =
1.2030200E+04 using 1615 PHA bins.
Reduced chi-squared = 7.5900314E+00 for 1585 degrees of freedom
Null hypothesis probability = 0.0000000E+00
untie bkg:104
renorm: no
renormalization necessary
Chi-Squared =
1.2030200E+04 using 1615 PHA bins.
Reduced chi-squared = 7.5948231E+00 for 1584 degrees of freedom
Null hypothesis probability = 0.0000000E+00
…
One
might then make a second pass at fitting the data, hopefully leading to
improved statistics. Subsequently, additional background model parameters could
be untied using the SPIuntie procedure as well. For example,
to untie three additional parameters over the full data set[2],
the command syntax is:
XSPEC>
SPIuntie bkg 475 19 1 3
…
This
will untie the first 3 parameters of the background model identified by "bkg", i.e. equivalent to issuing (475-1)´3 individual untie commands. Note that you
can always be reminded of the command-line argument definitions by typing
"SPIuntie -h" at the XSPEC prompt.
Suppose
now that you are satisfied with the relative background normalization terms,
and wish to freeze them at their current values for subsequent fitting passes. This
could be accomplished using the SPIfreeze command script:
XSPEC>
SPIfreeze bkg 475 -1
XSPEC12>SPIfreeze
bkg 19 1 -1
freeze
bkg:52 1
Chi-Squared =
6.6232600E+05 using 1805 PHA bins.
Reduced chi-squared = 3.7589444E+02 for 1762 degrees of freedom
Null hypothesis probability = 0.0000000E+00
freeze
bkg:78
Chi-Squared =
6.5791894E+05 using 1805 PHA bins.
Reduced chi-squared = 3.7318148E+02 for 1763 degrees of freedom
Null hypothesis probability = 0.0000000E+00
…
As
with the SPIuntie command script, typing "SPIfreeze -h" at the XSPEC prompt will scroll the
command-line definitions to your screen.
Excerpted From FTOOLS Help: SPIBKG_INIT:
SPIBKG_INIT (Sep
03) ftools.integral SPIBKG_INIT (Sep 03)
NAME
Spibkg_init --
Initialize input database for the XSPEC
"spibkg"
models that are used in the spectral deconvolution of INTEGRAL/SPI
data
USAGE
spibkg_init
inarf1 inarf2 inarf3 w_arf1 w_arf2 w_arf3 inpha
use_spiback spibackfil outfil
DESCRIPTION
The SPIBKG_INIT utility is used to
prepare INTEGRAL/SPI data
for analysis with the XSPEC (version 12 or
higher) spectral analysis
package. It should be run for each
individual SPI observation/data
analysis session. SPIBKG_INIT constructs a
database (FITS file) of
background spectral templates, and scaling
parameters, which are
customized for a given observation and
analysis. These data are then
read in to XSPEC upon the initialization
of one of the "spibkg"
models. In the few hundred keV to ~10 MeV spectral domain,
the
instrumental background is highly complex
- at least several hundred
strong, narrow and often time-variabe lines are present. It is variable
on a wide range of timescales as well as
from detector to detector, and
it is the
predominant component of the recorded counts for an
observation; typically less than ~1% are due to the astrophysical
source of interest. The usual procedures
used to subtract the
background in the few-to-tens of keV Xray domain would be
inadequate and lead to large systematic
errors and negative fluxes.
Nor is an empirical subtraction such as is
done with "chopping" mode
instruments such as CGRO/OSSE or
RXTE/HEXTE are not
applicable for coded-mask, high-resolution
spectrometer such as
INTEGRAL/SPI. Thus to perform a true, full
spectral deconvolution
one must simultaneously solve for source
plus background
components. The SPIBKG_INIT utility uses
observation-specific
information such as the degree of
individual detector shadowing for
the brightest sources within the field ov view, the recorded count
rates, the selected energy binning and net
exposure time per
instrument pointing. In addition, a
related utility, SPIBACK (which is
part of the INTEGRAL Offline Science
Analysis (OSA) software
package assembles information from other
sources, such as the
spacecraft scientific house-keeping
database, which can be read into
SPIBKG_INIT (see
<http://isdc.unige.ch/index.cgi?Soft+download>
For obtaining and installing INTEGRAL
OSA). In principle, this can
then be used to derive a more accurate
model of the instrumental
background (although at the time of this
release, SPIBACK's
capabilities are not fully developed. SPIBKG_INIT produces an
output FITS file, which is referenced by
XSPEC as an environment
variable, SPIBKG_INP_DAT, or directly as a
file named
"spibkg_inp_dat.fits"
that must reside in the XSPEC run directory.
PARAMETERS
inarf1 [string]
Component-1 arf file (generated by SPIARF) for a source of
interest. This file represents the
photo-peak effective area as a
function of energy, detector, and
dither pointing for a given
source position. It contains
information on the relative
shadowing with can be used in
initializing the background
model.
inarf2 [string]
inarf3 [string]
Similar to inarf1, for additional
sources in the observation
field of view. Note that more than 3
sources can be included in
the fit, but for the purposes of
initializing the background
model, a maximum of three (which are
anticipated to be the
brightest) is recommended.
w_arf1, w_arf2, w_arf3 [string]
Relative weighting factors to be
applied to the input arfs
(sources). For example, if there 2
sources are anticipated, and
one (for which arf1 hascomputed) is about twice as bright as
the other set w_arf1=2.0, w_arf2=1.0
and w_arf3=0.0. If only
one source is to be considered (which
will often be the case,
for example, in high-latitude
fields), then set w_arf1=1.0,
w_arf2=0 and w_arf3=0.
inpha [string]
Name of the type-II pha file (created by "SPIHIST")
containign
the detector-count spectral data that is being
analyzed.
use_spiback
[string]
Yes/No flag. If use_spiback="Y",
the information from the
"background model" (FITS)
file produced by the INTEGRAL
SPIBACK program will be used in
initializing the background
model database. SPIBACK extracts
information from the
observation science and house-keeping
data to derive
temporal and detector-to-detector
variations in the
observation. However, SPIBACK is a
complicated program
with a large number of options, some
of which are not fully
developed at present.
outfil [string]
Name of output FITS file. This should
either be named
"spibkg_inp_dat.fits",
and placed in your XSPEC run
directory, OR, named anything you
like, but referenced by an
environment variable called
SPIBKG_INP_DAT before you
run XSPEC.
EXAMPLES
1) An observation of the Crab nebula, which is
to a good approximation
an isolated point source. One component-1 arf file is used. The
weighting factor for that arf is set to 1.0, but this is not necessary in
this simple case. The PHA-II data file
upon which the analysis is
based is specified, and the option to use
the results from SPIBACK is
set to no. The SPIBACK output file nema is specified, but this is
superfluous since we chose not to use it.
inarf1,s,ql,"/mydir/rev0044_crab_cmp1.arf.fits",,,"Input
ARF file for source 1:"
inarf2,s,ql,"NONE",,,"Input
ARF file source 2:"
inarf3,s,ql,"NONE",,,"Input
ARF file source 3:"
w_arf1,s,ql,"1.0",,,"Relative
weighting factor for source 1:"
w_arf2,s,ql,"0.0",,,"Relative
weighting factor for source 2:"
w_arf3,s,ql,"0.0",,,"Relative
weighting factor for source 3:"
inpha,s,ql,"/mydir/rev0044.pha.fits",,,"Input
PHA file:"
use_spiback,s,ql,"N",,,"use information from SPIBACK to estimate
background? (Y/N):"
spibackfil,s,ql,"/mydir/spi/back_model.fits",,,"SPIBACK out
put file (or
"NONE"):"
outfil,s,ql,"spibkg_inp_dat.fits",,,"Output FITS file:"
2) An observation of the Cygnus region,
consisting a 19-detector, 5x5
dithering strategy has been analyzed,
leading to the type-II pha data
file "rev0022_cygnus.pha.fits".
The goal is to derive a spectrum for
Cygnus X-1. The second brightest
continuum, point gamma-ray
source in the observation field-of.view is Cygnus X-3, which we
assume is roughly 15% as bright as Cygnus
X-1. Note that other
weaker sources, such as Cyg X-2 or EXO 2030+375 may still be
analyzed using this initial background
model, even though they are
not considered in the "inarf" list. A sample parameter file follows:
inarf1,s,ql,"/mydir/rev0022_cygx1_cmp1.arf.fits",,,"Input
ARF file for source 1:"
inarf2,s,ql,"/mydir/rev0022_cygx3_cmp1.arf.fits",,,"Input
ARF file for source 2:"
inarf3,s,ql,"NONE",,,"Input
ARF file source 3:"
w_arf1,s,ql,"1.0",,,"Relative
weighting factor for source 1:"
w_arf2,s,ql,"0.15",,,"Relative
weighting factor for source 2:"
w_arf3,s,ql,"0.0",,,"Relative
weighting factor for source 3:"
inpha,s,ql,"/mydir/rev0022_cygnus_region.pha.fits",,,"Input
PHA file:"
use_spiback,s,ql,"N",,,"use information from SPIBACK to estimate
background? (Y/N):"
spibackfil,s,ql,"/mydir/spi/back_model.fits",,,"SPIBACK output file (or "NONE"):"
outfil,s,ql,"spibkg_inp_dat.fits",,,"Output FITS file:"
FILES NEEDED
All of the input files are produced by the
INTEGRAL OSA package:
type-II PHA spectral data file, associated
ARF ancilliary response
matrix files, and (optionally) the
background model file produced by
SPIBACK.
BUGS
SEE ALSO
Related utilities from the INTEGRAL (OSA)
suite: SPIHIST,
SPIRMF, SPIARF, SPIBACK.