A flattening in the optical light curve of SN 2002ap

Abstract

We present the UBVRc I c 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 I c 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 ~0.06M๏ ⁵⁶Ni mass. We also present low-resolution optical spectra obtained during the early phases. The Si II 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.