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

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 tc= 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.

Long-term evolution, X-ray outburst and optical/infrared emission of SGR 0501+4516

“…The unabsorbed 0.5-10 keV flux data points are from XMMNewton observations. The first five data points are taken from Rea et al (2009) and the sixth data point is taken from Camero et al (2014). The X-ray luminosity is calculated assuming a distance of 5 kpc.…”

“…For NH = 10 22 cm −2 (Rea et al 2009) we have converted the observed magnitudes when the X-ray luminosity is close to the quiescent level [i = 24.4 ± 0.4, u > 24.7, g > 26.9, K = 19.7 ± 0.1 (Dhillon et al 2011)] into the unabsorbed flux values. It is seen in Fig.…”

“…11) applied to the outburst model of Pons & Rea (2012). The first five data points are taken from Rea et al (2009) and the sixth data point is taken from Camero et al (2014).…”

Multi-instrument X-ray monitoring of the January 2009 outburst from the recurrent magnetar candidate 1E 1547.0-5408

“…In the last few years, six other faint X-ray sources underwent similar outbursts (X-ray flux variation of a factor ∼100). These sources were consequently classified as transient magnetars: 1E 1547.0-5408, CXOU J164710.2−455216, SGR 1627-41, SGR 0501+4516, 1E 1547.0-5408, SGR 0418+5729, and SGR 1833−0832 (Muno et al 2007;Israel et al 2007;Esposito et al 2008;Rea et al 2009;van der Horst et al 2010;Gögüş et al 2010;Esposito et al 2010). This suggested that presently known sources constitute only a fraction of a much larger, still undetected, magnetar population.…”

Monitoring the hard X-ray sky with SuperAGILE

“…Thus, only a handful of short bursts were imaged by SA, originating in SGR 1806-20, 1E 1547.0-5408, and SGR 0501+4516. The latter was indeed monitored during a dedicated target of opportunity observation approximately 10 days after its discovery, from 31st August to 10th September, but the source turned out to have gone back to an almost burst-quiescent state (see, e.g., Rea et al 2009) and only 2 short bursts were detected by SuperAGILE ). Examples of short bursts from the SGR sources detected by SA are shown in Fig.…”