POSSIBLE SUPERNOVA IN NGC 4622

R. Buta and G. G. Byrd (Univ. of Alabama)

T. Freeman (Bevill State Community College)

Images of the spiral galaxy NGC 4622 obtained with the Hubble Space Telescope from 2001 May 25.57- May25.91 (UT) reveal a likely supernova located 91.9 arcsec slightly east of north of the nucleus. The object is seen on four exposures in filters F336W (U), F439W (B), F555W (V), and F814W (I). The coordinates of the object are RA(J2000) = 12h 42m 40.04s, DEC(J2000) = -40o 43' 12.54". There is nothing at this position in the field of the galaxy seen on the Digitized Sky Survey. At the distance of 34 Mpc (Tonry et al. 2001, ApJ, 546, 681), this position projects 15 kpc from the nucleus, well outside the visible disk. Since there is no evidence of any massive star formation in this region, it is possible that the object is a Type Ia supernova. Its location so far from the center prevented it from being noticed when the images were first obtained.

The image of the possible supernova is saturated on all but the F336W image, which gives U=17.5 (May 25.6 UT). The apparent U-B color index is +0.3 or greater. After correcting for Galactic extinction, and referring to the U-band light curve of SN 1981b in NGC 4536 (Buta and Turner 1983, PASP, 95, 72), we estimate that our images were taken about 15-20 days past maximum light. If correct, we are now about 230 days past maximum, when the B-band magnitude would be about 6 mag below maximum (Kirshner 1990, Supernovae, A. G. Petschek, ed.) We estimate a likely apparent B magnitude of 21.5-22.0 and V magnitude of 21-21.5 as of January 16, 2002 (UT).

Digitized Sky Survey Image of NGC 4622. The circle and arrow show the location of the suspected supernova. North is to the top and east is to the left. The field shown is 5 arcminutes by 5 arcminutes in size.

HST WFPC2 F555W image of NGC 4622, rotated so that north is at the top and east is to the left. The arrow points to the suspected supernova.