Ginga Analysis


Overview of the Analysis

With analysis software provided here users can make (1) spectral analysis and (2) timing analysis from pointing-mode data. Detailed analysis of scan-mode data (such as fitting of the scan profile) is not supported at present.

LAC data analysis starts with selection of good time intervals (GTIs) defined by source visibility and background level. A tool (make_sf_list.pl) is supplied to calculate the GTIs. Referring to the GTIs, spectral files (ASCII format) and timing files (FITS format) are calculated from the FRFs. Because the ASCII format of the spectral files is unique to the LAC data, we afford a tool (lac2xspec) to convert it to the standard FITS format. The tool also produces an appropriate response matrix to the spectral file in the FITS format. In this procedure, background can be subtracted using several different methods. Model fitting will be done with general purpose tools, e.g., XSPEC. Some of the timing analysis may be done with the timing files using general tools, e.g., FTOOLS. However, we also supply some tools for the timing analysis, because the dead-time correction is mission dependent.


Install Analysis Software

A package containing analysis software for GINGA data analysis (the "GINGA tools"), calibration files, and other sample files is provided by the ISAS GINGA archives team. The GINGA tools, written in Fortran, are transplanted to the UNIX system from the original software developed on the ISAS main frame computers. Thus, the latest calibration made by the Japanese X-ray astronomy group is reflected in these tools.

Users can install them in either of the two ways.

  1. The simplest (and recommended) way is to download a package containing the executables of GINGA tools, which are available for Linux. If you untar them you will find the executables under bin/linux.
  2. Or users can download a package containing source codes and build the tools on their own systems. The provided Makefile supports OSF1, Linux, and SunOS. To install the tools follow steps according to INSTALL included in the package. The FTOOLS libraries must be installed before building the GINGA tools.

Warning: if you build the GINGA tools using a compiler that does not support REAL*16 type variables (such as g77), please keep in mind that the resultant time accuracy obtained by the GINGA tools timinfilfits and tim2filfits may not be sufficient for detailed timing analysis of some targets, such as millisecond pulsars. The distributed executables are free from this problem.


Test Software

The above package also contains calibration files (in the subdirectory "cal/"), template input/output files ("sample/"), test telemetry data ("frf/"), and a test script ("run_test"). With these files users can follow the same steps as written in the ABC manual.

1. Confirm the GINGA tools installed are included in your $path. To do this type e.g.,
> set path = ( /home/ueda/ginga_tools/v1.01/bin/linux $path )
2. Run the test script at the parent directory ("ginga_tools/v1.01").
> ./run_test
(In this test you need not set the GINGA_CALDIR and GINGA_FRFDIR environment variables as they are set by the script.)
3. Output files will be created in the "work/" directory.
4. To check the result you may compare the content of the output files under "work/" with the templates (expected results) under "sample/".
5. If this test is not successful, you may try the other installing method for the GINGA tools. If you still find troubles, contact "darts-admin @ ML.isas.jaxa.jp".
(In SunOS please ignore the following run-time messages. "Computing time differences using the 2 digit year from subroutine date is not safe after year 2000." "Note: IEEE floating-point exception flags raised: Inexact; Underflow; See the Numerical Computation Guide, ieee_flags(3M)".)

Get Telemetry Data

  1. Users can download telemetry data and LACDUMP files of specific observations upon their interests, utilizing the DARTS astrophysical database searching system.
  2. Or users can download all the telemetry data and LACDUMP files from the whole ISAS GINGA archives (1987-1991).

Analyze Data

To run the GINGA tools, the directory of LAC calibration files (included in the GINGA tools packages) must be pointed by the environment variable GINGA_CALDIR. The directory where the telemetry data are located must be pointed by the environment variable GINGA_FRFDIR. For example, type

>setenv GINGA_CALDIR /home/ueda/ginga_tools/v1.01/cal
>setenv GINGA_FRFDIR /home/ueda/ginga_tools/v1.01/frf

A step-by-step guide of GINGA data analysis is given in GINGA Data Reduction Guide (the ABC guide). Analysis after data reduction using the GINGA tools can be made by standard tools in XANADU (xspec, xronos), included in the HEAsoft package.


Caveat

  1. Time Accuracy

    There still remain some systematic uncertainties in the absolute time assignment in the telemetry files. Users are advised to read a note for details.

  2. Telemetry Overflow

    For observations of bright targets you need to care about telemetry overflow of the LAC. If the number of data events in a channel exceed 255 between successive readouts, the telemetry word overflows and the true number of events is lost. As a result, artificial structures (uncontinuous drops at certain bins) could appear in the energy spectrum. The limit of a source intensity causing overflow depends on the bit rate, the telemetry mode, and the setting of the coarse gain of the LAC, as summarized below (taken from Table 5 of Turner et al. 1989, PASJ, 41, 345).

    Source intensity causing overflow.
    Mode Coarse gain Bit rate
    High Medium Low
    MPC1 H 12 Crab 0.8 Crab 0.2 Crab
    L 5 0.4 0.1
    MPC2 H 24 1.6 0.4
    L 10 0.8 0.2
    MPC3 H 24 1.6 0.4
    L 10 0.8 0.2
    PC 4 0.5 0.1

Last Modified: 22 August 2014