UvA-DARE ( Digital Academic Repository ) GRB 030227 : The first multiwavelength afterglow of an INTEGRAL GRB

We present multiwavelength observations of a gamma-ray burst detected by INTEGRAL (GRB 030227) between 5.3 hours and∼1.7 days after the event. Here we report the discovery of a dim optical afterglow (OA) that would not have been detected by many previous searches due to its faintess ( R ∼ 23). This OA was seen to decline following a power law decay with indexαR = −0.95± 0.16. The spectral index βopt/NIR yielded−1.25± 0.14. These values may be explained by a relativistic expansion of a fireball (withp= 2.0) in the cooling regime. We also find evidence for inverse Compton scattering in X-rays.