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Astron. Astrophys. 324, 683-689 (1997)

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COMPTEL three-year search for galactic sources of 44 Ti gamma-ray line emission at 1.157 MeV

C. Dupraz 2, 5, H. Bloemen 2, 6, K. Bennett 4, R. Diehl 1, W. Hermsen 2, A.F. Iyudin 1, J. Ryan 3 and V. Schönfelder 1

1 Max-Planck-Institut für extraterrestrische Physik, P.O. Box 1603, D-85740 Garching, Germany
2 SRON-Utrecht, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
3 Space Science Center, University of New Hampshire, Durham NH 03824, USA
4 Astrophysics Division, ESTEC, 2200 AG Noordwijk, The Netherlands
5 Ecole normale supérieure, Radioastronomie millimétrique, 24 rue Lhomond, F-75231 Paris Cedex 05, France
6 Leiden Observatory, P.O. Box 9513, 2300 RA Leiden, The Netherlands

Received 6 September 1996 / Accepted 11 February 1997

Abstract

Because of its short lifetime, radioactive 44 Ti is a probe of the supernova activity of the Galaxy during the last few centuries. The COMPTEL experiment aboard the Compton Observatory is capable of imaging sources of 44 Ti line emission at 1.157 MeV with a sensitivity of about [FORMULA]. The latest known supernova remnant in the Milky Way, Cassiopeia A, has already been detected by COMPTEL (Iyudin et al. 1994). Although no further event has been observed for 300 years, young objects still obscured by interstellar extinction may also show up in the light of decaying 44 Ti.

Using the first three years of COMPTEL observations, we have carried out a systematic 1.157 MeV survey of the Galactic plane in order to search for these conjectural 44 Ti sources. We report on the following issues:

- of the six Galactic supernovae recorded during the last millenium, only Cassiopeia A is detected by COMPTEL. The updated flux, [FORMULA] (systematic uncertainty [FORMULA]), is lower than previously determined and implies an initial 44 Ti mass of 0.9 to [FORMULA] in better agreement with observational and theoretical pictures of the Cas A supernova;

- no serendipitous [FORMULA] Ti source is detected by COMPTEL at the [FORMULA] level, whereas we would expect 3 detections on statistical grounds. This negative conclusion is consistent at the [FORMULA] confidence level with canonical values of the Galactic supernova rate (2.5 to 3 events per century) and 44 Ti supernova yields (a few [FORMULA] to 1.157 MeV).

Key words: nucleosynthesis – gamma-ray: observations – supernovae: general; Cas A – ISM: supernova remnants

Send offprint requests to: H.Bloemen@sron.ruu.nl

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© European Southern Observatory (ESO) 1997

Online publication: May 26, 1998

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