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NuSTAR observations of the magnetar candidate SGR 1935+2154

ATel #7213; G. Younes (USRA/GWU), E. Gogus (Sabanci Univseristy), C. Kouveliotou (GWU), A. J. van der Horst (GWU) on behalf of a larger team
on 12 Mar 2015; 15:29 UT
Credential Certification: George Younes (gyounes@email.gwu.edu)

Subjects: X-ray, Neutron Star, Soft Gamma-ray Repeater, Transient

We observed the magnetar candidate SGR 1935+2154 with NuSTAR on 2015 February 27 as a Target of Opportunity, following the detection of tens of short soft bursts from the source with Swift/BAT and FERMI/GBM (GCNs: 17496, 17485). The observation resulted in a 50.6 ks livetime on the source.

Using data from both NuSTAR modules, FPMA and FPMB, we detect a periodic signal at P=3.24729(1) in the energy range 3-20 keV, at a 3.7 sigma significance (Z2 test, p-value=5E-4). Assuming this signal is the true spin period of the magnetar, and using the previous estimate of this source period as measured with Chandra (P=3.24498 s; ATEL #6370), we derive a spin down rate Pdot=1.45(2)x10^(-10) s/s. Interpreting the spin down rate as the result of magnetic braking, we derive a dipole field strength for SGR 1935+2154 of B=7x10^14 G.

We note that the NuSTAR period has been derived with a relatively low significance due to our faint signal detection. Deeper observations will be able to confirm our results.

We are grateful to the NuSTAR PI, Dr. Fiona Harrison, for approving the ToO.