The optical behaviour of ON 231 (W Comae) during and after the great outburst of spring 1998^*

¹ Dipartimento di Fisica e Osservatorio Astronomico, Universitá di Perugia, via A. Pascoli, 00000 Perugia, Italy
² Dipartimento di Fisica, Università “La Sapienza", P.zle A. Moro 2, 00185 Roma, Italy
³ Istituto di Astrofisica Spaziale, CNR, via del Fosso del Cavaliere 100, 00113 Roma, Italy
⁴ Osservatorio Astronomico di Torino, Strada Osservatorio 20, 10025 Pino Torinese, Italy
⁵ Dipartimento di Fisica Generale, Università di Torino, via P. Giuria 1, 10125 Torino, Italy

Corresponding author: G. Tosti, gino.tosti@pg.infn.it

Received: 5 February 2002
Accepted: 6 June 2002

Abstract

We present the results of the optical monitoring of the BL Lac object ON 231 from 1997 to the spring 2001, including the large outburst of spring 1998. After this event the mean source luminosity declined slowly and continued to show changes greater than one magnitude. A simple analysis of the variability time scales in the best–sampled segments of the light curve reveals that the luminosity changes were faster during the burst and slowed down in the subsequent years.