The exceptionally extended flaring activity in the X-ray afterglow of GRB 050730 observed with Swift and XMM-Newton

¹ ASI Science Data Center, via Galileo Galilei, 00044 Frascati, Italy e-mail: perri@asdc.asi.it
² INAF – Astronomical Observatory of Rome, via Frascati 33, 00040 Monte Porzio Catone (Rome), Italy
³ Department of Astronomy & Astrophysics, Pennsylvania State University, University Park, PA 16802, USA
⁴ INAF – Istituto di Astrofisica Spaziale e Fisica Cosmica, Sezione di Palermo, via La Malfa 153, 90146 Palermo, Italy
⁵ NASA/Goddard Space Flight Center, Greenbelt, MD 20771, USA
⁶ Department of Physics & Astronomy, University of Leicester, Leicester LE1 7RH, UK
⁷ INAF – Astronomical Observatory of Brera, via Bianchi 46, 23807 Merate, Italy
⁸ Università degli Studi di Milano-Bicocca, Dipartimento di Fisica, Piazza delle Scienze 3, 20126 Milano, Italy
⁹ Agenzia Spaziale Italiana, Unità Osservazione dell'Universo, Viale Liegi 26, 00198 Roma, Italy
¹⁰ Universities Space Research Association, 10211 Wincopin Circle, Suite 500, Columbia, MD, 21044-3432, USA

Received: 11 August 2006
Accepted: 27 March 2007

Abstract

Aims. We observed the high redshift () GRB 050730 with Swift and XMM-Newton to study its prompt and afterglow emission.

Methods. We carried out a detailed spectral and temporal analysis of Swift and XMM-Newton observations.

Results. The X-ray afterglow of GRB 050730 was found to decline along with time with superimposed intense flaring activity that extended over more than two orders of magnitude in time. Seven distinct re-brightening events starting from 236 s and up to 41.2 ks after the burst were observed. The underlying decay of the afterglow was well described by a double broken power-law model with breaks at t₁ = 237 ± 20 s and  ks. The temporal decay slopes before, between and after these breaks were = 2.1 ± 0.3, and , respectively. The spectrum of the X-ray afterglow was well described by a photoelectrically absorbed power-law with an absorbing column density  cm^-2 in the host galaxy. Evidence was found of flaring activity in the early UVOT optical afterglow, simultaneous with that observed in the X-ray band. Strong X-ray spectral evolution during the flaring activity was present. The rise and decay power-law slopes of the first three flares were in the range 0.8–1.8 using as zero times the beginning and the peak of the flares, respectively. In the majority of flares (6/7), the ratio between the duration of the event and the time when the flare peaks was nearly constant and ~ 0.6–0.7. We showed that the observed spectral and temporal properties of the first three flares are consistent with being due both to high-latitude emission, as expected if the flares were produced by late internal shocks, and to refreshed shocks, i.e. late time energy injections into the main afterglow shock by slow moving shells ejected from the central engine during the prompt phase. The event fully satisfies the – Amati relation but is not consistent with the E_p vs. E_jet Ghirlanda relation.