The 2008 OctoberSwiftdetection of X-ray bursts/outburst from the transient SGR-like AXP 1E1547.0-5408

• Published in: Monthly notices of the Royal Astronomical Society 2010-11, Vol.408 (3), p.1387
• Main Authors: Israel, G. L, Esposito, P, Rea, N, Dall'Osso, S, Senziani, F, Romano, P, Mangano, V, Götz, D, Zane, S, Tiengo, A, Palmer, D. M, Krimm, H, Gehrels, N, Mereghetti, S, Stella, L, Turolla, R, Campana, S, Perna, R, Angelini, L, De Luca, A
• Format: Article
• Language: English
• Subjects: Starbursts; X-ray astronomy
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1111/j.1365-2966.2010.17001.x

We report on the detailed study of the 2008 October outburst from the anomalous X-ray pulsar 1E1547.0-5408 discovered through theSwift/Burst Alert Telescope (BAT) detection of soft gamma-ray repeater like short X-ray bursts on 2008 October 3. TheSwift/X-ray Telescope (XRT) started observing the source after less than 100s since the BAT trigger, when the flux (6 × 10-11erg cm-2s-1in the 2-10 keV range) was >50 times higher than its quiescent level.Swiftmonitored the outbursting activity of 1E1547.0-5408 on a daily basis for approximately three weeks. This strategy allowed us to find a phase-coherent solution for the source pulsations after the burst, which, besidesPand, requires a positiveterm (spin-down increase). The time evolution of the pulse shape is complex and variable, with the pulsed fraction increasing from 20 to 50 per cent within theSwiftobservational window. The XRT spectra can be fitted well by means of a single component, either a power law (PL) or a blackbody. During the very initial phases of the outburst the spectrum is hard, with a PL photon indexΓ 2(orkT 1.4keV), which steepens toΓ 4(orkT 0.8keV) within one day from the BAT trigger, though the two components are likely present simultaneously during the first-day spectra. AnINTEGRALobservation carried out five days after the trigger provided an upper limit of2 × 10-11erg cm-2s-1to the emission of 1E1547.0-5408 in the 18-60keV band. [PUBLICATION ABSTRACT]