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Magnetars: Properties, Origin and Evolution

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Abstract

Magnetars are neutron stars in which a strong magnetic field is the main energy source. About two dozens of magnetars, plus several candidates, are currently known in our Galaxy and in the Magellanic Clouds. They appear as highly variable X-ray sources and, in some cases, also as radio and/or optical pulsars. Their spin periods (2–12 s) and spin-down rates (∼10−13–10−10 s s−1) indicate external dipole fields of ∼1013−15 G, and there is evidence that even stronger magnetic fields are present inside the star and in non-dipolar magnetospheric components. Here we review the observed properties of the persistent emission from magnetars, discuss the main models proposed to explain the origin of their magnetic field and present recent developments in the study of their evolution and connection with other classes of neutron stars.

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Notes

  1. Ironically, it is now known that the nebulae associated to two of the three first discovered SGRs are not supernova remnants.

  2. An updated list is maintained at http://www.physics.mcgill.ca/~pulsar/magnetar/main.html (Olausen and Kaspi 2014).

  3. The association with the supernova remnant N49 in the Large Magellanic Cloud yielded the distance and energetics of this event.

  4. In the lack of a better nomenclature, we use this adjective somehow improperly also for transient and variable sources, just to distinguish this emission from that of the short bursts and of the intermediate/giant flares.

  5. The MeV-GeV source in the region of 1E 2259+586 is well explained as emission from the supernova remnant CTB 109 interacting with molecular clouds (Castro et al. 2012).

  6. The extension to the general case has been derived by Nobili et al. (2008b), but only limited applications have been reported (Zane et al. 2011b).

  7. Several features have been observed during bursts, e.g.: emission lines at ∼13–14 keV in 1E 1048.1−5937 (Gavriil et al. 2002; An et al. 2014), in 4U 0142+61 (Gavriil et al. 2011), and in XTE J1810−197 (Woods et al. 2005); an absorption line at 5 keV (and possibly its harmonics) in SGR 1806−20 (Ibrahim et al. 2003); an emission line at 6.4 keV in SGR 1900+14 (Strohmayer and Ibrahim 2000).

  8. The estimate from 26Al is subject to systematic uncertainties (included in the quoted error), as the isotopic yield is model dependent, and there is an unknown yield contribution from local spallation processes and specific star-forming regions. This rate is broadly consistent with extragalactic estimates (Dahlen et al. 2012; Taylor et al. 2014) which are undifferentiated by galactic type, e.g. comparative studies in the Local Volume which are limited statistically by the small number of events (Botticella et al. 2012).

  9. X-ray Dim Isolated Neutron Stars, a class of relatively old, purely thermally emitting neutron stars discovered by the ROSAT satellite (see, e.g., Turolla 2009, for a review of their properties).

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Acknowledgements

We thank all the staff of the International Space Science Institute and the organizers of the stimulating Workshop “The Strongest Magnetic Fields in the Universe”. The work of SM has been partially supported through the agreement ASI-INAF I/037/12/0. JAP acknowledges support of the Spanish national grant AYA 2013-42184-P and of the New Compstar COST action MP1304. AM acknowledges support of an Australian Research Council Discovery Project grant and is grateful to Nicole Darman for assistance with typesetting.

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Correspondence to Sandro Mereghetti.

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Mereghetti, S., Pons, J.A. & Melatos, A. Magnetars: Properties, Origin and Evolution. Space Sci Rev 191, 315–338 (2015). https://doi.org/10.1007/s11214-015-0146-y

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  • DOI: https://doi.org/10.1007/s11214-015-0146-y

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