The X-ray afterglow of GRB 030329

Free access article

Issue		A&A Volume 409, Number 3, October III 2003


Page(s)		983 - 987
Section		Stellar atmospheres
DOI		http://dx.doi.org/10.1051/0004-6361:20031127

A&A 409, 983-987 (2003)
DOI: 10.1051/0004-6361:20031127

The X-ray afterglow of GRB 030329

A. Tiengo^{1, 2}, S. Mereghetti¹, G. Ghisellini³, E. Rossi⁴, G. Ghirlanda¹ and N. Schartel⁵

¹ Istituto di Astrofisica Spaziale e Fisica Cosmica - CNR, Sezione di Milano "G.Occhialini", Via Bassini 15, 20133 Milano, Italy
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
⁴ Institute of Astronomy, Madingley Road, Cambridge CB3 OHA, UK
⁵ XMM-Newton Science Operation Center, ESA, Vilspa, Apartado 50727, 28080 Madrid, Spain

(Received 30 May 2003 / Accepted 23 July 2003 )

Abstract
We report on XMM-Newton and Rossi-XTE observations of the bright (fluence ~10 ^-4 erg cm ^-2) and nearby ( z=0.1685) Gamma-Ray Burst GRB 030329 associated to SN2003dh. The first Rossi-XTE observation, 5 hours after the burst, shows a flux

decreasing with time as a power law with index $0.9\pm0.3$ . Such a decay law is only marginally consistent with a further Rossi-XTE measurement (at $t-t_{\rm GRB}\sim 30$ hr).

Late time observations of this bright afterglow at X-ray wavelengths have the advantage, compared to optical observations, of not being affected by contributions from the supernova and host galaxy. A first XMM-Newton observation, at $t-t_{\rm GRB}\sim 37$ days, shows a flux of $4\times10^{-14}$ erg cm ^-2 s ^-1 (0.2-10 keV). The spectrum is a power law with photon index $\Gamma=1.9$ and absorption < $2.5\times10^{20}$ cm ^-2, consistent with the Galactic value. A further XMM-Newton pointing at $t-t_{\rm GRB}\sim61$ days shows a flux fainter by a factor ~2. The combined Rossi-XTE and XMM-Newton measurements require a break at $t\sim 0.5$ days in the afterglow decay, with a power law index increasing from 0.9 to 1.9, similar to what is observed in the early part of the optical afterglow. The extrapolation of the XMM-Newton spectra to optical frequencies lies a factor of ~10 below simultaneous measurements. This is likely due to the presence of SN2003dh.

Key words: gamma rays: bursts

Offprint request: A. Tiengo, tiengo@mi.iasf.cnr.it

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