Status report #10:

September 6, 1991

SASS PROCESSING STATUS:

All PSPC data previously processed with SASS 5.1 (i.e., ROSAT days 256 to 276 = February 7-28, 1991) have been reprocessed using SASS 5.2 and are being redistributed to observers. As of September 5, 1991, data through day 285 had been processed. The rate of processing should be ~8-10 ROSAT days per week (assuming no major problems occur). SASS 5.3 (which will introduce a minor HRI bugfix) will be installed and tested by September 16 to coincide with the resumption of HRI data processing.

SASS releases are produced by MPE either to incorporate system changes or to correct for errors. If the errors produce faulty data then we will reprocess the affected data and redistribute to the users (as was done with ROSAT days 256-276, PSPC only). Such minor releases are thoroughly tested using ROSAT calibration data to ensure that the new SASS doesn't produce strange results.

Using background files for data analysis:

Extreme caution should be exercised in using the HRI or PSPC background maps provided on the PI data products tape.

HRI: The HRI background template is constructed using an internal detector background map (from ground based data), a soft X-ray background map (for unresolved celestial objects), a bright earth background map (from in-flight data), and a flat field charged particle background map (assumed to be flat). The soft X-ray and bright earth background maps reflect the vignetting of the mirror and also have 10% fluctuations due to the nonuniform response of the HRI. The contribution of the internal detector map in a given sequence is determined simply by multiplying by the live time of the observation. The contributions of the bright earth, soft x-ray, and charged particle maps are determined by fitting the maps to the data within the central 12', after all point sources have been removed. Because the relative levels of the background components have not yet been optimized using flight data, the background map may show a distinct peak (which comes from the region in which the quantum efficiency is highest). Several PCV observations are subject to this effect because the map normalization produced a bright-earth component with too large a weight compared to the flat-field particle background component. Changes will be made to the background map generation algorithm once sufficient sky data have been studied. In the meantime, users should be aware that background-subtracted data may show (spurious) fluctuations of ~10%, on a scale of several arc minutes.

PSPC: The background image is made by first excluding the regions of data affected by point sources. In the crowded field of a long observation this can come to a significant fraction of the field of view. A two-dimensional spline fit is then run on the remaining data. How well the spline fits the data depends a lot on how much data remain and on how noisy or smooth they are. Spurious structure in the background image is sometimes produced by the spline trying to work around strong gradients. Thus, when the image is used for background subtraction, false shadows can appear in the background subtracted data, and structure, particularly 4- or 8-point symmetry (due to smoothing over the ribs) can result. Unlike the data images, the background maps have not had their edges masked off; for some applications, users may need to do this themselves.

ANONYMOUS FTP ACCOUNT:

An anonymous FTP account has been set up at the GSFC Guest Observer Facility to provide outside users with ready access to the latest information about the the satellite, data analysis, and other information pertinent to ROSAT. To reach the account, type:

ftp rosserv.gsfc.nasa.gov

At the FTP login prompt, give the "username" as "ftp" (or "anonymous" - either one WITHOUT the quote marks). The "password" is your user identity (e.g., your username at your home institution). The account is "captured", which means a limited number of available directories and commands:

        command         function
        --------------  --------------------------------------
        dir             list files/directories 
        cd   Change Directory to 
        get       retrieve a copy of 
        status          show FTP's setup
        binary          toggle to binary (image) transfer mode
        ascii           toggle to ASCII (text) transfer mode

Once in the account, you can retrieve ("get") the file AAA_TAB_of_Cont to see a listing of what is currently available in the account.

ROSAT Target of Opportunity Observations:

It is possible, under unusual circumstances, to arrange target of opportunity observations using ROSAT. As with any satellite, a TOA must be an important observation of a time critical nature, that cannot be done within the confines of the normal observing program. Obvious examples are supernovae and X-ray transients. The only two TOA observations carried out to date were lunar occultations of bright galactic X-ray sources to measure the extent of the dust scattering halos. The following procedure should be used when applying for such an observation:

Verify that the target is observable by ROSAT, at the time of interest. Considering the limited sky coverage currently available, few targets will be observable.
If the target is observable, submit a formal request for the observation to the U.S. project scientist Steve Holt (LHEAVX::HOLT) and/or deputy project scientist Rob Petre (LHEAVX::PETRE). Include object name, coordinates in J2000, instrument configuration (PSPC or HRI), time/day of proposed observation, and a brief description of why this observation should be performed as a target of opportunity.
If the project scientist considers the observation appropriate, he will submit it toProf. Truemper, the ROSAT project scientist, for consideration. If Prof. Truemper accepts the observation, you will be notified and the observation will be scheduled.

Note that acceptance of a target of opportunity proposal does NOT automatically entitle the proposer to the data from that observation. Data rights are assigned as part of the normal international AO process.

Revised Budget for AO2 Proposals:

Now that the AO2 results and funding assignments have been distributed, we are soliciting revised budgets from all accepted proposers. Please use the forms that were included in the NASA Research Announcement covering AO2. If you have been funded to the level you requested in your proposal, you need not submit a revised budget.

Send revised budgets to: Doug Bennett Code 668 Goddard Space Flight Center Greenbelt, MD 20771 (301) 286-1512

Remember, we can't initiate your grant or contract without a revised budget.

Status of the ROSAT AMCS System:

During August the Attitude Measurement and Control System (AMCS) has worked in the reduced pointing mode without major malfunctions. The remaining hole in the all-sky survey was filled in the period August 3-13. As anticipated, it was not possible to initialize the standard 'scan-mode' because of too-large variations in the X-gyro drift rate. The survey was therefore performed in the 'standby-mode', without startracker reference. Once per day, the survey was halted for one orbit to perform an attitude update. On August 18th, there was a minor malfunction of the star camera, which was cured after a switch-off and internal self-test.

The update of the AMCS on-board software proceeds as planned. It is being done in two steps: the ASTRO-SPAS star acquisition software, an automatic on-board X-gyro drift compensation and a change in the definition of the steady-state bit have been tested and up-linked. This will allow smoother operations with less manual interaction. The attitude update with sun sensor and magnetometers is currently being coded. After a test period it should be uplinked (~mid September). GSOC should then be able to return to a more nominal pointing mode with several targets per day and access to the whole sky.

Timeline:

Only a two new targets have been added since the last status report:

15 Sept - 16 Sept US AM HER     Mauche
16 Sept - 17 Sept US U CEP      White

PROS:

The PROS distribution file is stored in an anonftp subdirectory, pub/pros/pros_1_1, containing the compressed and split distribution file, a CHECKSUMS file, a FILES.Z file, and this README file. The distribution file is a UNIX TAR file containing several directory trees from the PROS system: ./xray, ./proscal, ./einfits, ./rosfits. To facilitate transfers over unreliable network connections, the distribution file is split into 21 (512 Kb) files, requiring a total diskspace of 10.5 Mb. After the uncompress and tar, the PROS system (including calibration and demo data files) requires 27.5 Mb.

The files can be transferred as follows. These examples are for the SunOS version of FTP.

ftp -i sao-ftp.harvard.edu
[Name: anonymous]
[Password: ]
Set the current directory on both the local and remote systems.

ftp> cd pub/pros/pros_1_1
ftp> lcd //iraf
Transfer all the files in the distribution file directory. A binary transfer is required for the compressed tar files, and will work for the text files as well since both systems are UNIX.

ftp> binary

ftp> mget *

If problems are encountered, use the CHECKSUMS file to verify that any subfiles already transferred are correct. Delete any partially transferred subfiles and restart the transfer (by subfile we mean the 512 Kb files with extensions .00, .01, .02 etc. files making up the distribution file). Both BSD (Sun) and SYS5 checksums are given. The SunOS command "sum" will compute the checksum of a file.

Once all the files have been transferred the subfiles can be concatenated and uncompressed to reconstruct the original distribution TAR file, e.g.:

% cat pros1_1.* | uncompress | tar -xvf - FILES.Z. An easy way to look at a compressed text file such as FILES.Z is with "zcat":

% zcat FILES.Z | page

Remove the compressed, split files:

% rm -f *.Z

To build the PROS system, print out the postscript file: //iraf/xray/doc/install_guide.ps.

[Skip section 2, "Installing the XRAY Source Code", which refers to installation from tape.]

The following SUN patches are needed to compile the PROS software:

#1
for SUN OS 4.1.1 : 100174-03 (TMPFS patch to kernel)
for SUN OS 4.1 : 100089-05
"

#2
f77 1.3.1 patches: 100098-03, 100164-01
(Alternatively, installing f77 version 1.4 incorporates these patches)

If you encounter problems, please contact:

       
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