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ASCA AO-7 target list; FTOOLS v4.2; ASCA calibration update

ASCA Users,

This message includes 3 important items.

	I. ASCA AO-7 target list released
	II. FTOOLS v4.2 released
	III. ASCA calibration status update

	I. ASCA AO-7 target list released
The list of accepted AO-7 targets is now available from the ASCA GOF home
page at GSFC


(and will be posted on the ISAS ASCA home page sometime on Thursday,
1998 Dec 17).

US PIs will receive individual notifications in due course.  Although
the results of the national reviews/international merging are final,
transcription errors may exist, so the proposers are encouraged to check
this list.

	II. FTOOLS v4.2 released

We are pleased to announce the release of FTOOLS v4.2.

1. How to obtain FTOOLS v4.2

   FTOOLS v4.2 has been released, and can be obtained from the
FTOOLS web-page at:


This is where the most up to date FTOOLS information is available,
including notices of the FTOOLS Releases, online HTML versions of FTOOLS
documentation, and the continually updated FAQ.  Users should always check
here first for answers to questions.

Any problems installing FTOOLS should be reported to:


Any problems using FTOOLS for ASCA data analysis should be reported
to the ftoolshelp address above or to:


If the problem relates to the scientific contents of the FTOOLS,
the latter address is more appropriate.

2. ASCA-related changes.

addascaspec - Now works with previously added response files.

ascaarf - Fixed bug in generating arfs for GIS at 64x64 resolution.
                  Fixed bug that caused a crash if the GIS WMAP region was 
                  expanded to the whole detector (256 bins).

ascaeffmap - Fixed bugs in generating efficiency maps for SIS.

correctrdd - Fixed a bug in writing an output keyword, RDDCOR_V

extractor - Fixed detector images so that CTYPE do not imply RA & Dec
                  and comments do not mention degrees. 
	    Added support for regions in WCS coordinates (as written
                  by eg SAOtng).
            Changed the way the WMAP is handled in the case when the 
                  region filter is not in detector coordinates - now no
                  longer has the problem that pixels with no events are
                  flagged as outside the selected region. 
            Added Y2K compatibility.
            Fixed bug that always zeroed out the first channel of the 
                  output spectrum.
            Fixed bug in WMAP when WMAP binning differs from image binning.
            If a GTI filter file only has one table then assume that 
                  it is the correct one whatever the EXTNAME value.
            Sped up GTI filtering.
            Fixed bug causing WMAP CDELT to be set incorrectly to the 
                  image CDELT.

xselect - No longer require an @ in front of the filename of a list 
		of files for the read command.

	III. ASCA calibration status update
ASCA Calibration Update

We have been aware of the limitations of the current ASCA calibration:
In particular, below 1 keV, SIS-1 data are often well below the SIS-0
data, and GIS data rise above the SIS-0 data, up to ~20% at 0.7 keV.
[Note that the exact manifestation of the calibration limitations
varies on observing conditions, and on the source spectrum (as well as
how it is being modeled).]  We summarize below the current activities
to improve ASCA calibration.

We encourage all ASCA users to check our web pages regularly, to ensure
that you have the most up-to-date calibration information.  In particular,
we maintain a summary of calibration uncertainties at:


which we intend to update soon.

* XRT+GIS response

The calibration of XRT+GIS response is based on observations
of the Crab nebula.  It was assumed that such a high count
rate would change the gain (PHA vs E relationship), and this
has been modelled in deriving the XRT+GIS response from the
Crab data.  However, the GIS team has discovered that the situation
is more complex: it now appears that the high count rate has
a stronger effect on the electronics zero-point offset in the 
channel-energy relationship, than on the gain. In addition, 
the high counting rate may slightly affect the position 
determination in the peripheral region of the GIS detector, 
where the Fe-55 calibration isotope is attached. Via the gain
map, this effect may have mimicked a gain change.

The effort to understand this effect has introduced an additional
delay in revising the XRT+GIS response.  In this effort, the GIS
team has collected the latest experimental data on Au (on the XRT)
and Be (in the windows) optical constant; and refined the model for
the channel-energy relationship around the Xe L and M edges, and of
the electronic zero-point offset.  The GIS team is now close to converging
on updated XRT and GIS responses.  The new version can be made available,
in principle, within the next few months; however, this may cause unnecessary
confusion as the SIS calibration cannot be updated instantly.

* SIS Calibration

As soon as the GIS recalibration effort reaches a stable point, the
SIS team will commence the task of revising the SIS response.  In this,
they will use the new XRT response, and cross-calibrate SIS against GIS
using observations of 3C273 and other targets.

Independent of the above, the SIS team has been concentrating on four
areas that should improve the low-energy calibration of SIS.

(1) Updated CTI (Charge Transfer Inefficiency) tables: this will include
separate tables for 1, 2, and 4 CCD mode data.  It appears that the CTI
is clocking mode dependent, and the current CTI table is optimized 1-CCD
mode data.  The use of an inaccurate CTI table would lead to problems
particularly at low energies where the effective area depends strongly on

(2) New RDD distribution function: At launch, the dark current had a ~Gaussian
distribution around the mean.  As a consequence of radiation damage, the
distribution has become notably skewed over the years.  The current model
for this (RDD, or Residual Dark Distribution) appears inadequate for
recent observations.  The SIS team has a much improved description of the
distribution, and is in the process of deriving the model parameters as a
function of time.  When the new model is used for determining the zero levels,
it should improve the low energy calibration of the SIS.

(3) Variable spectral resolution across the chip: the column-to-column
variations of the CTI degrades the spectral resolution (this is the
major effect for 1-CCD mode data).  Currently, it is modeled as a function
only of time, most appropriate for a source observed at the standard 1-CCD
position.  This is inaccurate for sources observed elsewhere on the chip,
because this effect depends on the number of charge transfers.  The SIS team
is calibrating the position dependence of this effect.

(4) Effective detection efficiency of the SIS: the quantum efficiency
of the CCDs depends in part on how events are recognized and graded.
The combination of the RDD effect and of lower level discriminator
lowers the detection efficiency near the event threshold; the SIS team
is developing a quantitative description of this effect at the moment.

These four effects affects the SIS calibration particularly at low
energies.  SIS-1 data are affected worse than SIS-0 data; 4- and 2-CCD
mode data are affected worse than 1-CCD mode data.  We hope to release
the new CTI table within the next month, and we hope to begin testing
the variable spectral resolution model and the new RDD model at about
the same time.