SN 1998S

SN 1998S was a type IIn supernova that was detected in NGC 3877 in March 1998. At the time of discovery, SN 1998S was the brightest type IIn event observed,^[2] although later outshone by SN 2010jl.^[3]

SN 1998S

R-band image of SN 1998S in NGC 3877 obtained on 1998 March 16.1 ut at t he Jacobus Kapteyn Telescope (JKT), La Palma (north is up and east is to the left).[1]
Event type	Supernova
IIn
Date	c. 50.5 million years ago (detected 2 March 1998 by Z. Wan)
Constellation	Ursa Major
Right ascension	11h 46m 06.25s
Declination	+47° 28' 55.5"
Epoch	J2000.0
Galactic coordinates	150.7467 +65.9637
Distance	c. 50.5 million ly
Host	NGC 3877
Progenitor type	maybe Red supergiant
Colour (B-V)	~ 0.2 mag
Notable features	SN 1998S, AAVSO 1140+48
Peak apparent magnitude	12 mag
Other designations	SN 1998S, 2MASS J11460613+4728553, AAVSO 1140+48

It was discovered on 1998 March 2.68 UT in NGC 3877 by Z. Wan at a broadband (unfiltered) optical magnitude of +15.2.

Its spectrum showed prominent H and He emission lines with narrow peaks and broad wings, superimposed on a blue continuum. These narrow lines indicate the presence of a dense circumstellar medium (CSM) in the vicinity of the supernova. The high luminosity of SN1998S is due to the interaction of fast material (ejecta) with previously-expelled slowly-expanding material (CSM), which can more effectively convert kinetic energy of ejecta into radiation energy.^[4]