A flattening in the optical light curve of SN 2002ap

Abstract

We present the UBVR_cI_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, R_c 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, M_V=-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 M_⊙ 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 days.