SN 1998aq

SN 1998aq is a nearby supernova located in the intermediate spiral galaxy NGC 3982, offset $18 arcsecond$ west and $7 arcsecond$ of the galactic nucleus. It was discovered April 13, 1998 by amateur astronomer Mark Armstrong and was confirmed by fellow British amateur Ron Arbour; both members of the U.K. Supernova/Nova Patrol. The event was not visible on a prior check by Armstrong made April 7. It reached peak brightness on April 27, and 15 days later had declined by 1.14 magnitudes in the B (blue) band.

Spectroscopic observations determined this was a Type Ia supernova event, and it became one of the best-studied supernova of its type, at least in the visual band. An absorption feature of singly-ionized carbon was (probably) detected nine days before maximum, an indication of unburned ash left over from the original carbon-oxygen core of the progenitor white dwarf. Brightness calibration using Cepheid variables in NGC 3982 gives a peak absolute magnitude estimate of at least −19.47$$ (assuming no extinction in the host galaxy).