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Very fast optical flaring from a possible new Galactic magnetar


Highly luminous rapid flares are characteristic of processes around compact objects like white dwarfs, neutron stars and black holes. In the high-energy regime of X-rays and γ-rays, outbursts with variabilities on timescales of seconds or less are routinely observed, for example in γ-ray bursts1 or soft γ-ray repeaters2. At optical wavelengths, flaring activity on such timescales has not been observed, other than from the prompt phase of one exceptional γ-ray burst3. This is mostly due to the fact that outbursts with strong, fast flaring are usually discovered in the high-energy regime; most optical follow-up observations of such transients use instruments with integration times exceeding tens of seconds, which are therefore unable to resolve fast variability. Here we show the observation of extremely bright and rapid optical flaring in the Galactic transient4,5,6,7 SWIFT J195509.6+261406. Our optical light curves are phenomenologically similar to high-energy light curves of soft γ-ray repeaters and anomalous X-ray pulsars8, which are thought to be neutron stars with extremely high magnetic fields (magnetars). This suggests that similar processes are in operation, but with strong emission in the optical, unlike in the case of other known magnetars.

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Figure 1: Overview of overall optical high-time-resolution light curves of SWIFT J1955.
Figure 2: Detailed light curves of the two most prominent flares of the epoch 2007 June 11 of Fig. 1 .
Figure 3: Power spectral densities of the two prominent flares shown in Fig. 2 .


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We thank the Skinakas Observatory for their support and allocation of telescope time, and acknowledge the allocation of Chandra DDT time. We thank F. Schrey, T. Kougentakis and G. Paterakis for technical support, A. de Ugarte Postigo for access to private data taken simultaneous to some of our observations and A. Castro-Tirado for discussions. Skinakas Observatory is a collaborative project of the University of Crete, the Foundation for Research and Technology - Hellas, and the Max-Planck-Institute for Extraterrestrial Physics. A. Stefanescu acknowledges support from OPTICON. A. Słowikowska acknowledges support of the European Union through a Marie Curie Transfer of Knowledge Fellowship within the Sixth Framework Programme. S.McB. acknowledges the support of the European Union through a Marie Curie Intra-European Fellowship within the Sixth Framework Programme. G.S. is supported through DLR.

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Stefanescu, A., Kanbach, G., Słowikowska, A. et al. Very fast optical flaring from a possible new Galactic magnetar. Nature 455, 503–505 (2008).

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