OSSE Observations of Supernova 1998bu
M.D. Leising, L.S. The
Supernova 1998bu was discovered on May 9.9 in NGC 3368 (M
96), and was already present on a pre-discovery plate on May
3.1. SN 1998bu shows spectral and light curve properties
characteristic of a rather typical Type Ia supernova,
reaching a peak visual magnitude of V @ 11.9. This is
probably the nearest SN Ia in the Compton Observatory era,
offering the best chance yet for CGRO to detect 56Co
lines, as well as early 56Ni lines for some models.
Very early observations turned out to be impractical; the
first data were accumulated on days 18-21 post-explosion.
NASA committed a great deal of CGRO time to later
observations, including OSSE observations during the
intervals 26-53, 60-110, 117-137, 144-158, and 165-186
days. Together these data provide a line sensitivity at 847
keV of roughly 3 10-5 cm-2 s-1 averaged
over all these times. There is no convincing evidence for
56Co line emission in the OSSE data. The upper limits
rule out g-ray bright models, such as some
delayed-detonations. Reaching the ultimate sensitivity of
these data will require additional effort, as orbital
conditions at the current CGRO altitude are responsible for
unusually large and variable backgrounds.
File translated from TEX by TTH, version 2.32.
On 16 Jul 1999, 09:19.