A flattening in the optical light curve of SN 2002ap

Abstract

We present the UBVRcIc broad-band optical photometry of the Type Ic supernova SN 2002ap obtained during 2002 February 6-March 23 in the early decline phases and also later on 2002 August 15. Combining these data with the published ones, the general light-curve development is studied. The time and luminosity of the peak brightness and the peak width are estimated. There is a flattening in the optical light curve about 30 d after the B maximum. The flux decline rates before flattening are 0.127 +/- 0.005, 0.082 +/- 0.001, 0.074 +/- 0.001, 0.062 +/- 0.001 and 0.040 +/- 0.001 mag d-1 in U, B, V, Rc and Ic passbands respectively, while the corresponding values after flattening are about 0.02 mag d-1 in all the passbands. The maximum brightness of SN 2002ap, MV=-17.2 mag, is comparable to that of the type Ic 1997ef, but fainter than that of the type Ic hypernova SN 1998bw. The peak luminosity indicates an ejection of ~0.06 Msolar56Ni mass.

We also present low-resolution optical spectra obtained during the early phases. The SiII absorption minimum indicates that the photospheric velocity decreased from ~21 360 km s-1 to ~10 740 km s-1 during a period of ~6 d.