Dust-scattered X-ray halos around two Swift gamma-ray bursts: GRB 061019 and GRB 070129
INAF – Istituto di Astrofisica Spaziale e Fisica Cosmica Milano, via Bassini 15, 20133 Milano, Italy e-mail: email@example.com
2 Dipartimento di Fisica e Matematica, Università dell'Insubria, via Valleggio 11, 22100 Como, Italy
Accepted: 24 July 2007
Two new expanding X-ray rings were detected by the Swift XRT instrument during early follow-up observations of GRB 061019 and GRB 070129, increasing to 5 the number of dust scattering X-ray halos observed around GRBs. Although these two halos were particularly faint, a sensitive analysis can be performed that optimizes the method originally developed by Tiengo & Mereghetti (2006, A&A, 449, 203) to analyze dust scattering rings observed with XMM-Newton for the Swift satellite. In the case of GRB 061019, a known giant molecular cloud is identified as the one responsible for the scattering process, and its distance is accurately measured (d = 940 ± 40 pc) through the dynamics of the expanding ring. In the second case, XRT observed both the main peak of the prompt emission of GRB 070129 and the scattering halo, but the small number of detected halo photons prevents us from distinguish between different dust models.
Key words: gamma rays: bursts / methods: data analysis
© ESO, 2007