The first outburst of the new magnetar candidate SGR 0501+4516

Authors: Rea, N.; Israel, G. L.¹; Turolla, R.; Esposito, P.; Mereghetti, S.²; Götz, D.³; Zane, S.⁴; Tiengo, A.²; Hurley, K.⁵; Feroci, M.⁶; Still, M.⁴; Yershov, V.⁴; Winkler, C.⁷; Perna, R.⁸; Bernardini, F.¹; Ubertini, P.⁶; Stella, L.¹; Campana, S.⁹; van der Klis, M.¹⁰; Woods, P.¹¹

Source: Monthly Notices of the Royal Astronomical Society, Volume 396, Number 4, July 2009 , pp. 2419-2432(14)

Publisher: Wiley-Blackwell

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Abstract:

We report here on the outburst onset and evolution of the new soft gamma-ray repeater SGR 0501+4516. We monitored the new SGR with XMM-Newton starting on 2008 August 23, 1 day after the source became burst active, and continuing with four more observations in the following month, with the last one on 2008 September 30. Combining the data with the Swift X-ray telescope (Swift-XRT) and Suzaku data, we modelled the outburst decay over a 3-month period, and we found that the source flux decreased exponentially with a time-scale of t_c= 23.8 d . In the first XMM-Newton observation, a large number of short X-ray bursts were observed, the rate of which decayed drastically in the following observations. We found large changes in the spectral and timing behaviour of the source during the first month of the outburst decay, with softening emission as the flux decayed, and the non-thermal soft X-ray spectral component fading faster than the thermal one. Almost simultaneously to our second and fourth XMM-Newton observations (on 2008 August 29 and September 2), we observed the source in the hard X-ray range with INTEGRAL, which clearly detected the source up to ∼100 keV in the first pointing, while giving only upper limits during the second pointing, discovering a variable hard X-ray component fading in less than 10 days after the bursting activation. We performed a phase-coherent X-ray timing analysis over about 160 days starting with the burst activation and found evidence of a strong second derivative period component [ ]. Thanks to the phase connection, we were able to study the phase-resolved spectral evolution of SGR 0501+4516 in great detail. We also report on the ROSAT quiescent source data, taken back in 1992 when the source exhibits a flux ∼80 times lower than that measured during the outburst, and a rather soft, thermal spectrum.

Keywords: pulsars: general; pulsars: individual: SGR 0501+4516

Document Type: Research article

DOI: http://dx.doi.org/10.1111/j.1365-2966.2009.14920.x

Affiliations: 1: INAF - Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monte Porzio Catone (RM), Italy 2: INAF - Istituto di Astrofisica Spaziale e Fisica Cosmica, via E. Bassini 15, I-20133 Milano, Italy 3: CEA Saclay, DSM/Irfu/Service d'Astrophysique, Orme des Merisiers, Bât. 709, 91191 Gif sur Yvette, France 4: Mullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking, Surrey RH5 6NT 5: University of California, Space Sciences Laboratory, 7 Gauss Way, 94720-7450 Berkeley, USA 6: INAF - Istituto di Astrofisica Spaziale e Fisica Cosmica, via Fosso del Cavaliere 100, I-00133 Rome, Italy 7: Astrophysics Division, Research and Scientific Support Department, ESA-ESTEC, Keplerlaan 1, 2201 AZ Noordwijk, the Netherlands 8: JILA, University of Colorado, Boulder, CO 80309-0440, USA 9: INAF - Osservatorio Astronomico di Brera, Via Bianchi 46, I-23807 Merate (Lc), Italy 10: Astronomical Institute `Anton Pannekoek', University of Amsterdam, Science Park 904, Postbus 94249, 1090 GE, Amsterdam, the Netherlands 11: Dynetics, Inc., 1000 Explorer Boulevard, Huntsville, AL 35806, USA

Publication date: 2009-07-01

The first outburst of the new magnetar candidate SGR 0501+4516

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