NuSTAR DISCOVERY OF A 3.76 s TRANSIENT MAGNETAR NEAR SAGITTARIUS A*

Kaya Mori, Eric V. Gotthelf, Shuo Zhang, Hongjun An, Frederick K. Baganoff, Nicolas M. Barriere, Andrei M. Beloborodov, Steven E. Boggs, Finn Erland Christensen, William W. Craig, Francois Dufour, Brian W. Grefenstette, Charles J. Hailey, Fiona A. Harrison, Jaesub Hong, Victoria M. Kaspi, Jamie A. Kennea, Kristin K. Madsen, Craig B. Markwardt, Melania NynkaDaniel Stern, John A. Tomsick, William W. Zhang

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    Abstract

    We report the discovery of 3.76 s pulsations from a new burst source near Sgr A* observed by the NuSTAR observatory. The strong signal from SGR J1745-29 presents a complex pulse profile modulated with pulsed fraction 27% +/- 3% in the 3-10 keV band. Two observations spaced nine days apart yield a spin-down rate of (P) over dot = (6.5 +/- 1.4) x 10(-12). This implies a magnetic field B = 1.6 x 10(14) G, spin-down power (E) over dot = 5 x 10(33) erg s(-1), and characteristic age P/2(P) over dot = 9 x 10(3) yr for the rotating dipole model. However, the current (P) over dot may be erratic, especially during outburst. The flux and modulation remained steady during the observations and the 3-79 keV spectrum is well fitted by a combined blackbody plus power-law model with temperature kT(BB) = 0.96 +/- 0.02 keV and photon index Gamma = 1.5 +/- 0.4. The neutral hydrogen column density (N-H similar to 1.4 x 10(23) cm(-2)) measured by NuSTAR and Swift suggests that SGR J1745-29 is located at or near the Galactic center. The lack of an X-ray counterpart in the published Chandra survey catalog sets a quiescent 2-8 keV luminosity limit of Lx less than or similar to 10(32) erg s(-1). The bursting, timing, and spectral properties indicate a transient magnetar undergoing an outburst with 2-79 keV luminosity up to 3.5 x 10(35) erg s(-1) for a distance of 8 kpc. SGR J1745-29 joins a growing subclass of transient magnetars, indicating that many magnetars in quiescence remain undetected in the X-ray band or have been detected as high-B radio pulsars. The peculiar location of SGR J1745-29 has important implications for the formation and dynamics of neutron stars in the Galactic center region.
    Original languageEnglish
    Article numberL23
    JournalThe Astrophysical Journal Letters
    Volume770
    Issue number2
    Number of pages5
    ISSN2041-8213
    DOIs
    Publication statusPublished - 2013

    Keywords

    • Galaxy: center
    • pulsars: general
    • pulsars: individual (SGR J1745-29)
    • stars: neutron
    • ASTRONOMY
    • X-RAY PULSARS
    • SOFT GAMMA-REPEATERS
    • GALACTIC-CENTER
    • NEUTRON-STARS
    • RADIO PULSATIONS
    • EMISSION
    • OUTBURST
    • TELESCOPE
    • MECHANISM
    • DISK

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