The Last Days of ROSAT

ROSAT turned off on 12-Feb-1999 at 09:18:52 UT

The ROSAT observation campaign, started on December 8 with the PSPC in focus, has been terminated successfully despite numerous malfunctions of both the attitude control system and the PSPC operating system. A total of 21 objects were observed within 68 timeline slots, each of about 1000 sec duration. Contrary to our initial expectations the gas has not yet been completely used up.

On Friday, December 18, ROSAT was finally set into safemode, with its solar panels facing the sun thus ensuring its energy supply and safe telemetry connection. ROSAT will stay in this mode until January 1999.

Then we hope to activate the satellite again to carry out technical investigations with the ROSAT HRI and WFC instruments as proposed by our US and UK collaborators. Afterwards the PSPC will be switched on for the last time for observations of a few interesting X-ray sources until its gas is completely exhausted.

ROSAT has 'survived' the last weekend and is still operational. Obviously we have a little bit more detector-gas than originally supposed.

Meanwhile we could gather additional valuable data, e.g. again from comet C/1998 U5, SN 1979C, SN 1987A, and in addition from GB 1428+421 (a radio-loud quasar), from Nova LMC 1995 (the third post-nova with a supersoft X-ray spectrum) and from S 520 (a cluster of galaxies).

ROSAT is at the very end of its operation! For the last days, the PSPC has been reactivated again for a final set of observations. It will stay in focus until it runs out of gas. We have chosen a full-sun orbit period (dec 8 - 15) in order to minimize our attitude problems.

The sequence of events so far was:

• preparation of gassystem, rotating PSPC into focus on monday, dec 7.
• Switch on high voltage of PSPC, first observation on tuesday, dec 8.

The PSPC is observational since then, the observational efficiency, however, is rather low: the attitude is not quite stable and also the control computer of the PSPC shows some peculiarities, probably due to memory defects - no surprise after more than 8 years of bombardement by cosmic particles.

Scientific highlights (so far) were the observation of the supernova 1987A and the discovery of X-rays from the comet C/1998 U5 (see also IAU circular 7066). This is the tenth comet seen with ROSAT since the discovery of X-rays from comet Hyakutake in 1996! Other targets successfully oberserved are the supernovae SN 1979C, SN 1998S, the Active Galactic Nuclei 1ES 1927+654 and 1H 0707-495, and last but not least the recently discovered supernova remnant G 266.3-1.2 in the constellation Vela.