Late evolution of the X-ray afterglow of GRB 030329

¹ Istituto di Astrofisica Spaziale e Fisica Cosmica – CNR, Sezione di Milano “G.Occhialini”, via Bassini 15, 20133 Milano, Italy e-mail: tiengo@mi.iasf.cnr.it
² Università degli Studi di Milano, Dipartimento di Fisica, v. Celoria 16, 20133 Milano, Italy
³ INAF-Osservatorio Astronomico di Brera, v. Bianchi 46, 23907 Merate (LC), Italy

Received: 27 February 2004
Accepted: 7 April 2004

Abstract

The X-ray afterglow of the Gamma-Ray Burst GRB 030329, associated with SN2003dh at 0.1685, has been observed with XMM-Newton 258 days after the burst explosion. A source with a flux of (6.2 ± 2.3)  10^-16 erg cm^-2 s^-1 (0.5–2 keV) has been detected at the GRB position. This measurement, together with a re-analysis of the previous X-ray observations, indicates a flattening of the X-ray light curve ~40 days after the burst. This is in remarkable agreement with the scenario invoking the presence of two jets with different opening angles. The wider jet should be responsible for the observed flattening due to its transition into the non-relativistic Sedov-Taylor phase.