COMPTEL upper limits for the Co -ray emission from SN1998bu

Free access article

Issue		A&A Volume 394, Number 2, November I 2002


Page(s)		517 - 523
Section		Formation, structure and evolution of stars
DOI		http://dx.doi.org/10.1051/0004-6361:20021133

A&A 394, 517-523 (2002)
DOI: 10.1051/0004-6361:20021133

COMPTEL upper limits for the $^{\sf 56}$ Co $\gamma$ -ray emission from SN1998bu

R. Georgii^{1, 2}, S. Plüschke¹, R. Diehl¹, G. G. Lichti¹, V. Schönfelder¹, H. Bloemen³, W. Hermsen³, J. Ryan⁴ and K. Bennett⁵

¹ Max-Planck-Institut für extraterrestrische Physik, Postfach 1312, 85741 Garching, Germany
² FRM-II, Technische Universität München, Lichtenbergstr. 1, 85747 Garching, Germany
³ SRON Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
⁴ Space Science Center, University of New Hampshire, Durham, NH 03824, USA
⁵ Science Division, ESTEC, ESA, 2200 AG Noordwijk, The Netherlands

(Received 20 February 2002 / Accepted 1 August 2002 )

Abstract
Supernova 1998bu in the galaxy M 96 was observed by COMPTEL for a total of 88 days starting 17 days after the explosion. We searched for a signal in the 847 keV and 1238 keV lines of radioactive ⁵⁶Co from this type Ia supernova. Using several different analysis methods, we did not detect SN1998bu. Our measurements should have been sensitive enough to detect ⁶⁰Co gamma-rays as predicted from supernova models. Our $2\sigma$ flux limit is $2.3 \times 10^{-5}$ photons cm ^-2 s ^-1; this would correspond to 0.35 $M_{\odot}$ of ejected ⁵⁶Ni, if SN1998bu were at a distance of 11.3 Mpc and transparent to MeV gamma rays for the period of our measurements. We discuss our measurements in the context of common supernova models, and conclude disfavoring a supernova event with large mixing and major parts of the freshly-generated radioactivity in outer layers.

Key words: stars: supernovae: individual: SN1998bu -- gamma-rays: observations -- nucleosynthesis

Offprint request: R. Georgii, rgeorgii@frm2.tum.de

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