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.