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3. Suzaku Data Specifics and Conventions
This chapter describes the contents of Suzaku observation data sets,
including the directory structure, data files, and the format of those
files. The Suzaku data structure is similar to previous X-ray missions,
with small variations.
Public Suzaku data sets can be accessed through the HEASARC
Browse interface at GSFC which can be found at
can also be retrieved using wget or FTP.
For more details also see the Suzaku Archive GOF web page
wget or public FTP download works identical to the
proprietary data access (see next section), without the need for
decrypting the downloaded files.
In addition users can access the data at the ISAS DARTS site (mainly
intended for Japanese and European-based observers).
When the data are processed, the PI of the observation will receive an
e-mail from the Suzaku GOF at GSFC giving the FTP location to access and
download the data. For more information on the format of the location
ftp://legacy.gsfc.nasa.gov/suzaku/data/obs/M/NNNNNNNNN where M is a
number indicating the type of target and NNNNNNNNN the sequence number
of the data), please access the guide to the Suzaku archive at
We recommend to use wget to retrieve the data3.1:
wget --passive-ftp -q -nH --cut-dirs=5 -r 10 -c -N -np \
where the ftp_address_received is the location mentioned
Note that the ``/'' at the end of the command is required.
Alternatively, this can be done using the following FTP commands:
password : your_email_address@your_domain_address
ftp> cd suzaku/data/obs/M
ftp> get NNNNNNNNN.tar.gz
Once retrieved, they need to be decrypted using either PGP or GPG
software and a perl script available at the website
General information on how to decrypt the data is available at:
The decryption keys for Suzaku data are 32 or 34 characters long and
sometimes include special characters. We therefore recommend against
specifying the key on the command line. Also, with gpg, this process
will leave both the encrypted and decrypted versions of the files in
your data directory. You therefore need to make sure you have adequate
(original 2) disk space. Finally, glitches during download can
prevent decryption. If an initial attempt fails, re-downloading the
data set may be all that is required to successfully decrypt the data.
All Suzaku data (including ground calibration and test data) have unique
9-digit sequence numbers (e.g. 900000450) which is used as the
name of the top level directory. Under this directory are a series of
sub-directories, each of which carries a particular kind of data file,
as explained below. All the data files are in the standard FITS
format, although some output products are in Postscript, HTML, GIF or
simple ASCII. The subdirectories are:
- Auxiliary files not associated with a particular
instrument, such as the spacecraft attitude (file named
aeNNNNNNNNN.att - see Section 3.2 for an explanation
of the name structure) and the orbit file (file named
aeNNNNNNNNN.orb). The most important of these is the ``filter
file'' (with the suffix ``mkf''), in which various satellite and
instrumental parameters to be used for data screening are recorded
as a function of time.
- Log files from the pipeline processing.
- Data from the Hard X-ray Detector (HXD).
- Data from the X-ray Imaging Spectrometers (XIS).
Within each of the two instrumental directories (hxd, xis) there
are four subdirectories:
- Instrumental housekeeping files containing information such
as voltages, temperatures and other detector-specific data.
- Second FITS Files (SFF); these are unfiltered events
files derived from the First FITS Files (FFF). FFF are effectively
the telemetry data converted into FITS format.
- Cleaned events in this directory have gone through
the standard cuts (grades, SAA and such) and they are in principle
directly useful for analysis. However, users can re-run these
cleaning processes (see chapters 6 and 7 for
more on the standard cuts applied).
- Output products from the pipeline, such as GIF images
of the data and automatically generated lightcurves.
The filename conventions in each of these directories are
instrument dependent, as described in the next section.
The filenames (except for some log files) use the following general convention:
- is short for Astro-E2, the initial name of Suzaku.
- is the observation sequence number and is identical
to the directory name.
- is the instrument specification. This string is set as
follows: hxd=HXD, xi[0-3]=XIS-[0-3]. xis is used for files common to
all the XIS units. This string can be omitted in files under the
auxil and log directories.
- ranges from 0 to 9 and indicates the RPT file number. The
original telemetry file is divided into RPT files and more than one
RPT can contribute to one observation. The value of 0 is used when
the science file combines data from different RPT or if there is
only one RPT file that contributes to that sequence. This number can
be omitted in files under the auxil and log directories.
- is the file identifier. The string distinguishes
between files from the same instrument.
- indicates the file level. For event files, the string can be
``uf'' or ``cl'' to indicate ``unfiltered'' or ``cleaned'' event
files. It also can be ``bg,'' ``sk,'' ``sr,'' ``gso,'' ``pin,''
``wel'' (products directory for both the XIS and HXD) or
``wam'' ( hk directory for the HXD). The string can be
- is the file extension. Currently it can take the values:
``evt'' (event files), ``gti'' (good time interval), ``hk'' (house
keeping), ``ghf'' (gain history file), ``ght'' (gain history table),
``lc'' (light curve), ``pi'' (pulse invariant), ``html,'' ``log,''
``com,'' ``att'' (attitude file), ``cat,'' ``ehk,'' ``mkf,''
``orb,'' ``tim,'' ``img,'' and ``gif.''
For more information on file names of the products of the pipeline
processing, please refer to the documentation that can be found
3.3 Suzaku Coordinates
The XIS is an imaging instrument (unlike the HXD), and the coordinate
values in XIS files indicate the pixel center positions. The XIS
coordinate systems are described below:
- Sky coordinates
- ``X'' and ``Y'' are used to describe the sky
positions of the events relative to a celestial reference point.
The tangential projection is used, and north is defined up
(increasing Y), and east is left (decreasing X). ``X'' and ``Y''
columns are computed using attitude information.
- Focal plane coordinates
- These are the event locations on the
focal plane, which is common to the four (there are four XIS
detectors) imaging instruments. ``FOCX'' and ``FOCY'' event file
columns are used. The FOC coordinates differ from the Sky images in
that the satellite attitude is not considered in the former. FOC
images of the four instruments should match, as instrument
misalignments are already taken into account.
- Detector coordinates
- These give the physical positions of the
pixels within each sensor. Misalignments between the sensors are
not taken into account. The DET X and Y values take 1 to 1024 for
XIS. The XIS DETX/Y pixels correspond to the actual 1024x1024 CCD
pixels, and the DETX/Y pixel size is the same as the CCD physical
pixel size. The DET images will give correct sky images of the
objects (not mirrored images), except that attitude wobbling is not
taken into account. Note that X-ray images focused by the mirrors
and detected by the focal plane instruments will be the mirror
images, which have to be flipped to be the actual images of
celestial objects. Thus, the original look-down images are flipped
(and rotated if necessary) so that the satellite +Y-axis direction
will be the DETY direction.
- ACT and RAW coordinates
- The ACT coordinates are used to tell
actual pixel locations on the chip. Each XIS chip is composed of the
four segments, and the RAW coordinates are the pixel locations on
each segment. Note that the XIS-0 and XIS-3 installations on the
baseplate are aligned, whereas XIS-1 and XIS-2 are 90 degrees
rotated relative to them, in opposite directions
respectively. Therefore the relation between ACT and DET coordinates
is dependent on each XIS sensor.3.2
Types of coordinates and coordinate related variables
and their possible values.
All Suzaku instruments are energy-sensitive, and each event has a
measured ``Pulse Height Amplitude'' (PHA). The PHA may be both
position- and time-varying, depending upon the instrument. Therefore,
a calculated ``PHA Invariant'' (PI) value is also determined using the
PHA in combination with the instrumental calibration and gain drift.
In all cases, the PI columns should be used to extract energy spectra,
or to produce energy-band selected images or light curves. For
reference, the approximate relationship between ``true'' X-ray energy
E and the event PI is shown below for each instrument. The exact
relationship between energy and PI is given in the second extension of
the instrument response matrix file, or ``RMF.''
- The PI column name is ``PI'', which takes values from 0 to
4095. The PI vs. energy relationship is the following: [eV] =
- The ``PI_SLOW'' column (as opposed to ``PI_FAST''), which
takes values from 0 to 511, should be used for GSO spectral
analysis. The PI vs. energy relationship is the following:
[keV] =2(PI_SLOW + 1.0), where is the center of the
bin. For PIN spectral analysis, the ``PI_PIN'' column which takes
values from 0 to 255, should be used. The value in this column is
copied from the PI column of the triggered PIN, which is one of the
PI_PIN0, PI_PIN1, PI_PIN2 or PI_PIN3. The PI vs. energy
relationship is the following: [keV] =0.375(PI_PIN +
1.0), again is the center of the bin.
The Suzaku event arrival time is represented by the ``Suzaku time'', which
is defined as the elapsed time in seconds from the beginning of the
year 2000 (January 1st, 00:00:00.000) in UTC (when TAI is 32 seconds
ahead). There will always be a constant offset between TT and Suzaku
time, and this is reflected in the time-related keywords. These and
other systems of time are documented at:
The event time resolution of each detector as follows:
- In the Normal observation modes (5x5, 3x3, or 2x2) without a
Window option, the time resolution is 8sec, corresponding to a
single frame exposure. The event time assigned is the midpoint of
the exposure frame. When the Window option is used, depending on its
size, the time resolution will be 2s (1/4 Window), or 1s (1/8
Window). In Timing mode, the time resolution is 7.8125ms,
regardless of the number of lines to be combined (either 64, 128, or
256). Users should note that when combining a small number of
lines, there could be a noticeable amount of cross-talk between one
time bin and the next, due to the wings of the PSF. For example, 64
lines is only about 1.2arcmin, so a fraction of the source counts
will fall on the neighboring groups of 64 lines, and so be
mis-time-tagged by +/-N times 7.8125ms. For this reason, it may be
safer to always use a grouping of 256 lines.
- The nominal time resolution is s, which
corresponds to the HXD_WPU_CLK_RATE_HK parameter = 1 (Fine). A
higher time resolution, s is possible within the
requirements of satellite operations, in which case
HXD_WPU_CLK_RATE_HK will be 2 (Super-Fine), although this is not
user-selectable at this time.
The telemetry rate determines the data transfer rate from the onboard
instruments to the Data Recorder. Being limited by the data storage
and downlink capacity, the highest data rates may not be used all the
time3.3. Basically, a combination of the
following three telemetry rates will be used for observations: High
rate (261kbps), Medium rate (131kbps), or Low rate
(33kbps) 3.4. Among the 10
Gbit raw data per day, 4 Gbits will be taken between the contacts
(contact passes) with High and Medium bitrates, and 6 Gbits will be
taken after the contacts (remote pass) using Medium and Low bitrates.
Although the maximum Data Recorder recording rate is limited by the
telemetry rate for each bitrate, allocation of the telemetry to
various instruments is variable. The XIS and HXD telemetry limits
depend on the bitrates.
- The approximate XIS telemetry limits (events/s per XIS
unit) - as in use since the loss of XIS2 in 2006 November
- for different bitrates and editing modes is given in
Telemetry limits (in events/s per XIS unit) - as in
use since the loss of XIS2 in 2006 November - for different XIS
These numbers do not include overheads (telemetry header and HK) and
background event rates (FI10/s/sensor; BI20/s/sensor). Allow for a 10% margin.
||FI 2x2 / BI 3x3
Modification of telemetry saturation limit by window/burst options:
1. No window s burst option - telemetry limit increases times.
2. window s burst option - telemetry limit increases times.
3. Area discrimination will further increase the telemetry limit.
XIS events are compressed on-board and actual telemetry limits may
vary within % depending on the PHA values. Note that
different XIS sensors may be operated using different modes and
- The approximate HXD Well telemetry limits will be the
following (in counts/s): Super-High=1150, High=550, Medium=250, and
Low=30. This is based on the assumption that HXD will take 30% of
the telemetry. Note that the Crab rate in the HXD is cts/s.
3.7 XSELECT Default Parameters
The XSELECT behavior for each mission is determined by the
mission database file, usually located at
Suzaku entries in the mission database files enable the following:
- Common for all the instruments:
- Default light curve bin size is 16sec.
- ``extractor'' is used to extract products.
- WMAP3.6 is created
as the spectral file header.
- Default image coordinates are Sky coordinates (X and Y).
- Default WMAP coordinates are Detector coordinates (DETX and DETY).
- Event file has one of the following names; ae*xis0*.evt,
ae*xis1*.evt, ae*xis2*.evt, ae*xis3*.evt, or ae*hxd wel*.*.
- The filter file has the name ae*mkf*, and is in the
directory ../../auxil relative to the event file
- Default image binning is 8.
- Default WMAP binning is 8.
- ``RAWX'' and ``RAWY'' coordinates are set to ``ACTX'' and
``ACTY'', so the ``set image raw'' command creates ACT coordinate
- Pixels in the WMAP outside of the selected region will have
the value ``-1''
- Spawns ``grppha'' when saving a spectral file, three speed
options - ``fast'', ``medium'', ``slow'' - are
available. ``Medium'', the default, results in the following
channel binning: 1 from channel 0 to 699, 2 from
700 to 2695, and 4 from 2696 to 4095. Channels 0-81 and
1645-2047 are flagged as ``bad'' (original PI channels 0-81 and
- Spawns ``xisrmfgen'', ``xissimarfgen'', ``marfrmf'', and,
optionally, ``rbnrmf'' when saving a spectral response file, with
the three speed options mentioned above. Again, ``Medium'' is the
- The default energy column to make energy spectra is
``PI_PIN'' for a PIN event file and ``PI_SLOW'' for a GSO event
- The UNITID event file column is used in lieu of standard X,
Y, RAWX, RAWY and DETX of imaging instruments, so that the
``sky'' or ``raw'' images will be a pseudo-diagonal image of
- The PIN_ID event file column (defined only for DET_TYPE =
1) is used in lieu of DETY, so that the WMAP is created with
UNITID vs. PIN_ID, which is useful when creating ARFs and RMFs
for the PIN.
- No binning for ``image'' and WMAP.
- PIN and GSO spectra are saved with the original number of
channels, i.e., 256 and 512, respectively.
- ... data3.1
- wget is available at:
- ... sensor.3.2
- Conversion from the RAW to
ACT coordinates is not straightforward, because of the particular
order of the pixel read-out and possible use of the Window
- The amount of the data taken per day is mainly limited
by the capacity of the Data Recorder (6 Gbits) and the downlink rate
at Uchinoura Space Center (2 Gbits/ground contact). There will be 5
ground contacts per day separated by 90 minutes, so not more than 10
Gbits/day raw data can be taken, with typical daily sizes being
considerably smaller than this.
- In addition, there is a Super-High rate (524
kbps) which is not used for general observations.
- Users may specify their own mission
database file with an environmental parameter XSELECT_MDB.
- ... WMAP3.6
- WMAP is the part of the detector image from
which the energy spectrum has been extracted, and will be used
to create spectral responses by downstream FTOOLS.
- ... directories3.7
- For Suzaku FTOOLS
Version 13 and earlier the filter file has to be uncompressed
or the file name has to be explicitly specified.
- ... UNITID3.8
- For each HXD event, UNITID and DET_TYPE tell the
Well unit-ID and the detector type, respectively. UNITID takes
a value in the range of 0 to 15 corresponding to the 16 Well
units. DET_TYPE = 0 corresponds to the GSO, and DET_TYPE=1 to
Next: 4. Suzaku Data Analysis
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