The Sleeping Monster: NuSTAR Observations of SGR 1806–20, 11 Years After the Giant Flare

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dc.citation.articleNumber17en_US
dc.citation.journalTitleThe Astrophysical Journalen_US
dc.citation.volumeNumber851en_US
dc.contributor.authorYounes, Georgeen_US
dc.contributor.authorBaring, Matthew G.en_US
dc.contributor.authorKouveliotou, Chryssaen_US
dc.contributor.authorHarding, Aliceen_US
dc.contributor.authorDonovan, Sophiaen_US
dc.contributor.authorGöğüş, Ersinen_US
dc.contributor.authorKaspi, Victoriaen_US
dc.contributor.authorGranot, Jonathanen_US
dc.date.accessioned2018-07-02T18:19:42Zen_US
dc.date.available2018-07-02T18:19:42Zen_US
dc.date.issued2017en_US
dc.description.abstractWe report the analysis of five Nuclear Spectroscopic Telescope Array (NuSTAR) observations of SGR 1806−20 spread over a year from 2015 April to 2016 April, more than 11 years following its giant flare (GF) of 2004. The source spin frequency during the NuSTAR observations follows a linear trend with a frequency derivative $\dot{\nu }=(-1.25\pm 0.03)\times {10}^{-12}$ Hz s−1, implying a surface dipole equatorial magnetic field $B\approx 7.7\times {10}^{14}$ G. Thus, SGR 1806−20 has finally returned to its historical minimum torque level measured between 1993 and 1998. The source showed strong timing noise for at least 12 years starting in 2000, with $\dot{\nu }$ increasing one order of magnitude between 2005 and 2011, following its 2004 major bursting episode and GF. SGR 1806−20 has not shown strong transient activity since 2009, and we do not find short bursts in the NuSTAR data. The pulse profile is complex with a pulsed fraction of $\sim 8 \% $ with no indication of energy dependence. The NuSTAR spectra are well fit with an absorbed blackbody, ${kT}=0.62\pm 0.06\,\mathrm{keV}$, plus a power law, ${\rm{\Gamma }}=1.33\pm 0.03$. We find no evidence for variability among the five observations, indicating that SGR 1806−20 has reached a persistent and potentially its quiescent X-ray flux level after its 2004 major bursting episode. Extrapolating the NuSTAR model to lower energies, we find that the 0.5–10 keV flux decay follows an exponential form with a characteristic timescale $\tau =543\pm 75$ days. Interestingly, the NuSTAR flux in this energy range is a factor of ~2 weaker than the long-term average measured between 1993 and 2003, a behavior also exhibited in SGR 1900+14. We discuss our findings in the context of the magnetar model.en_US
dc.identifier.citationYounes, George, Baring, Matthew G., Kouveliotou, Chryssa, et al.. "The Sleeping Monster: NuSTAR Observations of SGR 1806–20, 11 Years After the Giant Flare." <i>The Astrophysical Journal,</i> 851, (2017) IOP Publishing: https://doi.org/10.3847/1538-4357/aa96fd.en_US
dc.identifier.doihttps://doi.org/10.3847/1538-4357/aa96fden_US
dc.identifier.urihttps://hdl.handle.net/1911/102331en_US
dc.language.isoengen_US
dc.publisherIOP Publishingen_US
dc.rightsArticle is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use.en_US
dc.titleThe Sleeping Monster: NuSTAR Observations of SGR 1806–20, 11 Years After the Giant Flareen_US
dc.typeJournal articleen_US
dc.type.dcmiTexten_US
dc.type.publicationpublisher versionen_US
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