NuSTAR discovery of a 3.76 second pulsar in the Sgr A* region

ATel #5020; Kaya Mori, Eric V. Gotthelf (Columbia University), Nicolas M. Barriere (UC Berkeley), Charles J. Hailey (Columbia Univerity) , Fiona A. Harrison (Caltech), Victoria M. Kaspi (McGill University), John A. Tomsick (UC Berkeley), Shuo Zhang (Columbia University)
on 27 Apr 2013; 05:40 UT
Credential Certification: Jules Halpern (jules@astro.columbia.edu)

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Following detection of flaring from the Galactic center (ATel #5006, #5008, #5011, #5013, #5014) we initiated a 40 ks NuSTAR X-ray observation of Sgr A* on 2013 April 26, 1:00:06 UT. From an initial 21 ks of data that spanned 64 ks we detected enhanced X-ray emission in the 3-10 keV X-ray band approximately 3 times greater than previous NuSTAR survey observations of the same field. The count rate increased to 0.38 cts/s/module within a 30 arcsecond radius aperture around the Sgr A* as compared to 0.11 cts/s/module in the 2012 October observation.

A blackbody plus power-law spectral model yields a temperature of kT = 0.85 keV and photon index of Gamma = 3.2 and is statistically preferred over a single power-law. The 3-10 keV unabsorbed flux is 2.4e-11 erg/cm2/s corresponding to a luminosity of 1.8e35 erg/s at d=8 kpc.

For a preliminary timing analysis we searched a total of 16,497 photon arrival times extracted from the combined pair of Focal Plane Modules on-board NuSTAR using a 30 arcsecond radius aperture centered on the peak X-ray emission. The arrival times were binned into a 2 ms resolution light curve and searched for coherent pulsations using an FFT to the Nyquist frequency. We find a complex signal around 3.76 seconds with power at odd harmonics. A refined Z^2_3 analysis gives a preferred period of P=3.7635417(80) seconds corresponding to a pulse profile with three resolved peaks each 0.6 s wide, dominated by a single strong peak. A summary plot is available at http://www.astro.columbia.edu/~eric/sgra_transient_timing.ps

The bursting, timing, and spectral properties strongly suggest a previously unknown magnetar undergoing an outburst. Further observations are planned to follow the flux and spectral evolution as well as to measure the spin-down rate and to search for additional bursts. NuSTAR has triggered additional ToO observations. Additional radio observations of the field, particularly to search for radio pulsations, are encouraged.

NuSTAR Pulsar Summary Plot