BROWSE can be used to manipulate data files. They can either be extracted
and placed in the current directory, or transparently passed to an analysis
program for further anlysis. The latter avoids the data extraction process
and the need to use file names to identify the data products.
This chapter concentrates on finding which data products are available,
using the pp command to obtain a quick overview by making a plot, and
using the xp command to extract the products and place them in the
user's current directory.
The lfiles command gives a listing of the data files available with
the current database. For example,
ROSUSPSP_PUBLIC_DEC > lfiles
Loading ZZFNAME and ZZFILES, please wait...
Qualifier File Obs Inst Type Format Description
----------+-----------+--------+--------+--------+--------+----------------
EVENTS PEV2 ROSAT PSPC PHOTLIST FITS master data stor
EVENTS PEV1 ROSAT PSPC PHOTLIST FITS photon list
IMAGE PIM3 ROSAT PSPC IMAGE FITS soft-band image
IMAGE PIM2 ROSAT PSPC IMAGE FITS hard-band image
IMAGE PIM1 ROSAT PSPC IMAGE FITS broad-band image
---------------------------------------------------------------------------
Type XP or PP/Qualifier[=File,...] to access the data product[s]
This shows not only the products but also the qualifier that is used
to access the file. If lfiles/plot is given then only those files that
can be plotted will be listed. The available files vary from database
to database and it is essential to use lfiles first to find out whats
available.
To plot a spectral product, type pp/sp n where n specifies the entry numbers
to plot. The default uses the current entry. The default plot will be a
histogram. Error bars are given if the /errorbars option is used.
In some cases, a background spectrum is also provided. This is accessed
by using pp/bgspec.
These spectral plots are designed to give a quick overview of the spectrum.
For X-ray detectors, the spectra consist of count rate versus channel number.
XSPEC is used to fit spectral models to these spectra and convert the spectrum
to photons versus energy. In some cases, the spectrum is background
subtracted, but in others it is not. For spectra from other wavebands, the
spectra may be already calibrated (such as the IUE ULDA). The ``Available
Databases User's Guide" gives further information on this and other details
about the spectrum. It is essential that this be read carefully before these
spectra are used.
To plot an image product associated with one or more entries, use pp/im.
The image will be 256x256 pixels, centred on the RA and Dec of the entry.
The image can also be plotted centred on different pixel coordinates by
specifying /x=i/y=j where i and j are the x and y pixels. The pixel
coordinate convention depends on the telescope and again the ``Available
Databases User's Guide" must be consulted. The number of pixels in the
image can be changed using the /size=num option where num specifies the
number of pixels displayed. Num can be any integer between 2 and 1024.
The image display is made via the XIMAGE package. Using the XIMAGE command
can give the ability to manipulate the image directly.
There are several options to plot the various lightcurves that may be
available in a database. The ``Available Databases User's Guide" provides
more details. The pp command uses the XRONOS package to plot these
lightcurves. The XRONOS programs can also be run directly from BROWSE
on the selected entries and this gives more freedom to specify
the plot parameters. The pp command allows users to obtain a plot
without the need to go deeply into the various options possible
with XRONOS.
There are a number of options used to control the plot.
The default binning for the lightcurves is optimized to the count rate.
To specify the required binning, use /bins=nn where nn is the desired
number of bins. For example, pp/li/bins=50.
If more than one entry number is specified for a lightcurve plot, such as
pp/li 1 2 5-8, then the default is to to produce one lightcurve
for each entry number. The user will be prompted to type ``return" between plots.
To plot the specified entries on a single lightcurve, the /oneplot
qualifier is used.
If only one entry number is specified, all lightcurves with the same
sequence number as the given entry will be concatenated and
plotted together unless the /individual qualifier is specified.
This automatic concatenation is included since it is likely that users
will want to examine all entries from the same observation together.
The /chi option plots the lightcurve and lists various statistical
quantities, including the .
For those lightcurves for which multiband data is available, it is possible to
plot the hardness ratio of the count rate in the two bands against count rate
using pp/hardness. The count rate will be the sum of the two bands. Use
pp/hard1 or pp/hard2 to plot the hardness ratio versus the intensity in
only the low energy band and only the high energy band, respectively.
Data product files are extracted from the database and placed in the user
directory with the xfiles (extract files) command. This command simply
copies the file to the current directory.
The /name= qualifier is used to rename the file(s), otherwise the
default filename will be the one under which the file is stored in
the database.
If no qualifier is given specifying which product is to be extracted, then
for each product the user will be prompted regarding whether to extract it.
The /all qualifier will extract all available files.
In the following example, 5 EXOSAT ME spectra from cyg x-1 are extracted
with the name ``cygx1":
ME_TOTAL_DEC > xfiles/sp/name=cygx1 1-5
Loading ZZFNAME and ZZFILES, please wait...
Extracting s49883.pha SPECTRAL SF Argon 1-15 keV >> cygx1.pha;1
Extracting s30325.pha SPECTRAL SF Argon 1-15 keV >> cygx1.pha;2
Extracting s34881.pha SPECTRAL SF Argon 1-15 keV >> cygx1.pha;3
Extracting s55494.pha SPECTRAL SF Argon 1-15 keV >> cygx1.pha;4
Extracting s23299.pha SPECTRAL SF Argon 1-15 keV >> cygx1.pha;5
Note that BROWSE has added a version number with an underscore to the
file name in order to avoid name conflicts.
In this example, all lightcurves and spectra are extracted using the
/all option.
ME_TOTAL_DEC > xfiles/all 10
Extracting r37134.rbf 1 of 2 LIGHTCURVE RBF 0.8-8.9 keV 30 s background >> r37
134.rb
Extracting r37145.rbf 2 of 2 LIGHTCURVE RBF 0.8-8.9 keV 30 s background >> r37
145.rbf
Extracting d37134.rbf 1 of 2 LIGHTCURVE RBF 0.8-8.9 keV source >> d37134.rbf
Extracting d37145.rbf 2 of 2 LIGHTCURVE RBF 0.8-8.9 keV source >> d37145.rbf
Extracting a37134.rbf 1 of 2 LIGHTCURVE RBF 0.8-3.6 keV 1-10 s source >> a3713
4.rbf
Extracting a37145.rbf 2 of 2 LIGHTCURVE RBF 0.8-3.6 keV 1-10 s source >> a3714
5.rbf
Extracting b37134.rbf 1 of 2 LIGHTCURVE RBF 3.6-8.9 keV 1-10 s source >> b3713
4.rbf
Extracting b37145.rbf 2 of 2 LIGHTCURVE RBF 3.6-8.9 keV 1-10 s source >> b3714
5.rbf
Extracting c37134.rbf 1 of 2 LIGHTCURVE RBF 0.8-8.9 keV 1-10 s source >> c3713
4.rbf
Extracting c37145.rbf 2 of 2 LIGHTCURVE RBF 0.8-8.9 keV 1-10 s source >> c3714
5.rbf
Creating file using VIMAT
File s37145.rsp RESPONSE SF Argon 1-15 keV in current directory
Extracting s37145.pha SPECTRAL SF Argon 1-15 keV >> s37145.pha
In some cases, the product extracted may be created at the time of extraction
using the value of a parameter in the database. An example of this is the XSPEC
spectral file created from the EXOSAT LE count rate in a particular filter. In
such cases, it is not worth using disk space to keep the spectral files. Such
cases should be obvious to the user.
The XSPEC spectral fitting program can be run from BROWSE to make spectral fits
on selected spectral files. XSPEC is run from command files which are created
by BROWSE. A check is made to find out whether response matrices for the
requested spectra are available; if not, they are created by VIMAT in the
current user's directory. When XSPEC is started, it has all of the file names
for data and response in the command files and the user does not need to worry
about them. XSPEC also automatically opens LOG and HISTORY files with the same
names as the .pha file but with extensions .xlg and .xhs, respectively.
The log files provide an ASCII record of the XSPEC session.
XSPEC/int leaves XSPEC in an interactive mode and the user can carry out
more spectral analysis on the current data.
XIMAGE is a multi-mission X-ray image display and analysis facility which can
be invoked from BROWSE. The display and graphic capabilities of XIMAGE use the
PGPLOT graphic package, which supports most graphic terminals and workstations.
SAOIMAGE is an X-windows display package which can be invoked from BROWSE.
Typing ximage from BROWSE will automatically display a 256x256 image centered
on the source (or field) corresponding to the current entry in the database
(assuming there is an image associated with that record). After the command is
executed, control is returned to BROWSE. The XIMAGE command syntax is
identical to that of BROWSE and can be entered directly from the BROWSE command
line. For example,
CMA_SOURCES_DEC > ximage 33
loads and displays an image for entry 33. The /int qualifier leaves XIMAGE in
an interactive mode from which all XIMAGE commands are then available (see the
``XIMAGE User's Guide" for details). To return to BROWSE, type exit or quit
or bye.
XRONOS is a general-purpose timing analysis package which can use rate buffers
or QDP files as input and incorporates a question/answer and command-driven
user interface. Any XRONOS application can be run in command-driven fashion
from the command line of BROWSE on the currently selected entries. Flexibility
is achieved by specifying qualifiers in the command string and by running
dedicated utilities which control the overall XRONOS session. Most XRONOS
applications produce by default a XRONOS QDP output file (xronos.q*** where
*** is the XRONOS command name) which is displayed automatically by using
QDP/PLT. The /plt qualifier leaves QDP/PLT in the interactive mode from
which the plot can be modified and fitted at will. The reader is referred to
the ``XRONOS User's Guide" for further details.
The XRONOS applications are listed by typing xronos on the BROWSE command
line as follows:
ME_TOTAL_DEC > xronos
acs ---> xronos: auto-correlation
acf ---> xronos: auto-correlation (FFT)
cpf ---> xronos: change param file
asc ---> xronos: convert to ASCII
ccs ---> xronos: cross-correlation
ccf ---> xronos: cross-correlation (FFT)
efs ---> xronos: epoch folding search
ef1 ---> xronos: fold single lightcurve
ef3 ---> xronos: fold three lightcurves
ef2 ---> xronos: fold two lightcurves
lda ---> xronos: list rbf/qdp file
win ---> xronos: make windows
psd ---> xronos: power spectrum (FFT)
pss ---> xronos: power spectrum
lc1 ---> xronos: single lightcurve
sta ---> xronos: statistics
lc3 ---> xronos: three lightcurves
tss ---> xronos: time-skewness
lc2 ---> xronos: two lightcurves
Applications lc2 and ef2 include options to plot the hardness
ratio versus time or count rate of any of the two lightcurves or the sum
of them. Applications lc3 and ef3 include a plot option to plot
the soft and hard hardness ratios in a colour-colour diagram.
There are the following four basic entities in most XRONOS applications:
BINS : These are the time bins of the time series being analyzed.
Note that there can be more than one bin duration. For example, two consecutive
time series, one with 0.5 s bins and the other with 2 s bins, as in the
example below.
NEWBINS : These correspond to the time resolution with which the analysis is
carried out. The example below shows how to calculate the power spectrum using
a 4 s resolution, that is, newbins of 4 s. Note that: (i) newbins cannot be
shorter than the longest bin duration of the time series being analyzed; (ii)
in many XRONOS applications (such as psd, pss, acf, ccf) the newbin
duration is forced to be an integer multiple of the longest bin duration.
INTERVALS : An interval is defined by the number of newbins over which
the analysis is carried out. The example below shows how to calculate
power spectra for intervals of 256 newbins, corresponding to 128
independent Fourier frequencies. Note that in applications using FFT
algorithms (such as psd, acf, ccf), the number of newbins in an
interval must be a power of 2.
FRAMES : A frame consists of the average of the results of the analysis
of one or more contiguous intervals. Each XRONOS QDP file and, therefore,
each plot produced by XRONOS corresponds to a frame. The example below
shows how to average the power spectra from 5 intervals (each of 256 newbins
of 4 s) in a frame. Note that in certain applications (such as lc1, lc2
and lc3), a frame always consists of one interval.
Suppose that entry no. 42 corresponds to two time series (rate buffers)
with 0.5 s bins and 10000 s duration and 2 s bins and 20000 s durations,
respectively. In this case, the application psd sets the newbin
duration by default to produce a power spectrum from a single
interval of 4096 newbins at most. Therefore,
ME_TOTAL_DEC > psd 42
sets the newbin duration to 8 s, corresponding to 3750 newbins,
calculates the power spectrum from a single interval of 4096 newbins
(empty newbins are replaced with the average count rate), writes
the file xronos.qpsd, and plots the power spectrum with 2048 independent
Fourier frequencies.
ME_TOTAL_DEC > psd/tnewbin=4. 42
or, equivalently, (note that the longest bin in the time series is 2 s)
ME_TOTAL_DEC > psd/nint=2 42
sets the newbin duration to 4 s, corresponding to 7500 newbins. In this
case, psd calculates the power spectra from two intervals of 4096 newbins
(the default) averages the results in a frame, writes the file xronos.qpsd
and plots the average power spectrum with 2048 Fourier frequencies.
ME_TOTAL_DEC > psd/tnewbin=4./nbins=256 42
specifies also that each interval consists of 256 newbins. In this case,
the power spectra from 29 intervals are calculated (128 independent
Fourier frequencies) and averaged by default in a single frame to
produce a single output file xronos.qpsd and plot it.
carries out the analysis as above, except that the power spectra from
(up to) 5 consecutive intervals are averaged in a frame, written to
the output file xronos.qpsd, and plotted, thus producing a
sequence of 6 average power spectra.
For each XRONOS command there are a number of allowed qualifiers used to
control the execution of each command. These are listed by using /? as
for any BROWSE command. For example,
ME_TOTAL_DEC > lc1/?
The following BROWSE qualifiers (see command pp) are used in
XRONOS applications in order to specify the type of lightcurve product to be
analyzed:
Many XRONOS qualifiers are specific to a single application or group of
applications. XRONOS-specific qualifiers which are most commonly used are as
follows:
Number of newbins in an interval. With the newbin time, it determines the
interval duration and, therefore, the number of intervals over which the
analysis will be carried out (I=integer; I<0 to have nbins=2-I).
Number of times the (longest) bin integration time in input file(s) is rebinned
to give the newbin duration (I=integer) (not available in ef1, ef2,
ef3 and efs).
Newbin durations (in seconds) to be used in the analysis. The default is to
produce a single interval with a number of newbins which changes from one
application to another (X=real) (not available in ef1, ef2, ef3 and
efs).
In addition to the flexibility achieved by using the XRONOS qualifiers and by
specifying time, phase, intensity, and exposure windows with application win,
a number of parameters controlling the overall XRONOS session can be specified
by running application cpf. These include utilities to
write to a log file and specify the log file chattiness
change the default output filename root and i/o status
replace data gaps with a moving average of the lightcurve(s)
force a given start time in the analysis
calculate error bars for the results of various types of analysis
by propagating theoretical error bars or by direct evaluation of the
scatter around the mean values in a frame
analyze window functions
normalize the results in various ways
force strict simultaneousness in time series from two or three energy
bands, for example, for cross-correlation analysis
specify special windows for burst analysis
specify a rescaling factor and an additive constant for the results.
.
For those lightcurves for which multiband data is available, it is possible to
plot the hardness ratio of the count rate in the two bands against count rate
using pp/hardness. The count rate will be the sum of the two bands. Use
pp/hard1 or pp/hard2 to plot the hardness ratio versus the intensity in
only the low energy band and only the high energy band, respectively.