Interest in the ROSAT archive has been high. The archive has received over a hundred requests for nearly one thousand data files during the month of December alone. Requests have been received from all over the US as well as Europe and the People's Republic of China. Since the opening of the archive in November 1992, some changes have been made to the availability of data, as well as some enhancements to the capability to view data on-line. This article will discuss these recent changes.

New rule on availability of incomplete observations

In many cases ROSAT observations are obtained in separate spacecraft pointings which occur months (or years) apart. When the archive opened in November 1992 it was the policy of the ROSAT International User's Committee that such pointings would enter the archive incrementally; that is, the first pointing would enter the archive 54 weeks after the data were distributed to the PI, the second pointing would be added to the data from the first pointing and would enter the archive 54 weeks after distribution to the PI, and so on. This policy was thought not to violate proprietary data rights, since by definition the incomplete observation would not be sufficient for the science proposed by the PI. However, this policy caused some uneasiness in the community and, as a result, the IUC decided to abandon it in December 1993. The new policy adopted by the IUC is that no data shall enter the archive until the accepted exposure time is greater than or equal to 70% of the exposure time requested by the PI. This means that the proprietary clock doesn't start ticking until the PI has received data having at least 70% of the requested exposure. The only exception to this rule would be if it became clear that the observation would not acquire the requisite 70% exposure (due, for example, to the demise of the PSPC). In such a case the observation would be declared "completed" and the normal rules for making the data public would adhere (i.e. the data would enter the archive if 54 weeks elapsed since the distribution of the data to the PI).

This new rule had an immediate impact on the archive in that 22 datasets (4 HRI and 18 PSPC) which had been made available to the public in November had to be withdrawn from circulation. A list of these data sets follows:

     RH200005       RH300009
     RH500023       RH900010
     RP200008       RP200028
     RP200045       RP200046
     RP200047       RP200049
     RP200052       RP200068
     RP200099       RP200102
     RP200107       RP200113
     RP200117       RP700062
     RP800032       RP800034
     RP800051       RP900001

Archive users should check the accepted exposure time with the requested exposure time for any observation of interest before requesting it from the archive. Archive users can do this in either of two ways:

1) MIPS users of the DistribList database can use the DisplayPage function to determine the requested exposure and the actual exposure obtained.

2) BROWSE users can use the "dpage" (display page) command to determine the requested versus actual exposure time for any observation of interest.

Availability of MPE-Processed Data

The exchange of data between processing centers at MPE and GSFC started in December 1992. At time of this writing, data to be made public through the end of 1992 has been exchanged between both sites. Unforutnately, technical difficulties have delayed ingest of the MPE data into the US archive (and the ingest of the US data into the German and UK archives). These difficulties have to do primarily with the content and format of the "public contents files" which are associated with each data set and which are used to create a catalog of archive contents at each archive site. However, these difficulties have been all but ironed out and it is expected that by the time this goes to press public data from German and UK observers will be available to US archive users.

Initially, data processed by MPE will be ingested into the US archive in the so-called ROD FITS format. Though this format is significantly different from the US PROS FITS format familiar to most US ROSAT observers, software is available within PROS to analyze data in the ROD format.

Archive users in the US will be able to use MIPS and BROWSE to examine which German/UK data are available, and to request that data. In the meantime MPE has made available a list of all German/UK data in the MPE archive through 28 Feb 1993. This data will also be ingested into the US archive. Archive users in the US who wish to determine what German/UK data will be available in the US can access this file via anonymous ftp from heasarc.gsfc.nasa.gov. The file is called mpe_archive_contents.txt. The file can be found under the rosat/doc/archive directory. (Note that the HEASARC anonymous ftp accounts will be re-organized in the early part of 1993, which means that the location of this file will change. An announcement will be made when this change is made).

Archive users can use MIPS or BROWSE to request German/UK data from the US archive in much the same manner as US data. Archive users can also send e-mail requests for German/UK data to the Automated Retrieval Mail Service on NDADS directly. ARMS requesters should realize that the naming convention of the German/UK data is different from that used by the US. The table below lists the ARMS data-type descriptions for German/UK PSPC and HRI datasets. ARMS users should send an e-mail message to NDADSA::ARCHIVES with the subject line reading REQUEST ROSAT <DATA TYPE> where <DATA TYPE> is one of the 6 listed below (no POSTSCRIPT data type exists for data processed by MPE). The body of the e-mail should contain one or more entry-ids, where an entry-id is given by wp<ror> or wh<ror>. Thus wp110130 is an allowable entry-id.

NDADS
DATA TYPE           File description          Sample file
FITS                photon list               wp110130_events.tfits
                    broad-band image          wp110130_image.ifits
                    hard-band image           wp110130_imagehard.ifits
                    soft-band image           wp110130_imagesoft.ifits
                    energy-coded image        wp110130_imageenergy.ifits
                    SIMBAD source list        wp110130_simbad.tfits
                    Exposure map              wp110130_exposure.ifits
BASIC               photon list               wp110130_events.tfits
                    rejected events           wp110130_difevents.tfits
DERIVED             broad-band image          wp110130_image.ifits
                    hard-band image           wp110130_imagehard.ifits
                    soft-band image           wp110130_imagesoft.ifits
                    SIMBAD source list        wp110130_simbad.tfits
                    energy-coded image        wp110130_imageenergy.ifits
CALIBRATION         response matrix           wp110130_drmpspc.tfits
                    instrument map            wp110130_instrmap.ifits
                    Off-axis area, pspc b     wp110130_effarea_pspcb.tfits
                    Off-axis area, pspc c     wp110130_effarea_pspcc.tfits
                    exposure map              wp110130_exposure.ifits
ANCILLARY           Quality file              wp110130.quality
                    attitude file             wp110130_attitude.tfits
                    event rates               wp110130_eventrates.tfits
                    orbit                     wp110130_orbit.tfits
ALL                 all the above             all the above

NDADS
DATA TYPE     	    File Description          Sample File
FITS                photon event list         wh110131_events.tfits
                    SIMBAD sky list           wh110131_simbad.tfits
BASIC  		    photon event list         wh110131_events.tfits
                    rejected events           wh110131_difevents.tfits
DERIVED SIMBAD      sky list                  wh110131_simbad.tfits
CALIBRATION  	    effective area            wh110131_effarea_hri.tfits
                    hot spot map              wh110131_hotmat.ifits
                    quantum efficiency map    wh110131_qefficiency.tfits
ANCILLARY  	    aspect                    wh110131_attitude.tfits
                    event rates               wh110131_eventrates.tfits
                    orbit                     wh110131_orbit.tfits
                    data quality              wh110131_qualitylimits.tfits
                    data quality limits       wh110131_quality.tfits
ALL                 all the above             all the above

New BROWSE features

See the article "HEASARC On-line Service" on page 70.

US Archive Problems

Archived versions of 2 datasets (RH800050 and RP500019) were found to contain corrupted files. In the first case the problem was seen in the events list file (the ".fits" file) while in the second case the problem was found in the soft-band image file. The problem was thought to be due to the controller of the magnetic disk used to stage the data by NDADS before writing to optical disk. As a result, access to the archived data was turned off for about a week while the magnetic disk and controller were replaced. Copies of all the data that was previously archived using the "bad" controller were re-copied to the archive using the "good" controller. NDADS has instituted another level of routines to help insure the validity of the data on optical disk, as as of this writing no known problems exist in the versions of the ROSAT data stored in the NDADS archive. Any discovery of corrupt or unusual-looking data from the archive is asked to report it at once to Dr. Michael Corcoran at the address below.

Non-electronic data requests

It is expected that most users of the ROSAT archive will request and copy data from the archive electronically. However, some users may have limited network access. There are also cases in which the volume of data requested is so large that network transfer of the data is not feasible. In these (and other) instances users may wish to have data sent to them on magnetic tape. Requests for ROSAT data on magnetic media should be sent to NCF::REQUEST or to Dr. Michael Corcoran at the address below.

Questions/comments/complaints about the US ROSAT Public Data Archive should be addressed to

Dr. Michael Corcoran
Code 668
Goddard Space Flight Center
Greenbelt MD 20771
HEASRC::CORCORAN
corcoran@heasrc.gsfc.nasa.gov

Proceed to the next article

Return to the previous article

Select another article