1 Introduction

Among the GRBs detected by BeppoSAX and Rossi-XTE for which an optical transient (OT) has been proposed, GRB 970228, GRB 980326 and GRB 980519 showed a fast initial fading. The existence of an OT related to GRB 971227 (Castro-Tirado et al. 1997; Bartolini et al. 1997) is less firmly established. If this could be confirmed, there would be growing evidence for a GRB population with short-lived afterglows. Here we present and briefly discuss the results of the optical observations on the error box of the X-ray afterglow of GRB 971227.

 

Figure 1: Part of the R frame taken at Calar Alto on Dec. 27.9. The proposed OT is located in the upper right hand region of the error circle of 1SAX J1257.3+5924 (radius: $1\hbox{$.\mkern-4mu^\prime$}5$), inside the smaller circle in the darker band. Size of the field: $4\hbox{$.\mkern-4mu^\prime$}24 \times 4\hbox{$.\mkern-4mu^\prime$}24$. The limiting magnitude is $R\sim20.5$. North is at top, East is to the left