X-ray observations play a crucial role in understanding the emission mechanism and relevant physical phenomena of magnetars .
We report X-ray observations of a young magnetar SGR 1900+14 made in 2016 , which is famous for a giant flare in 1998 August .
Simultaneous observations were conducted with XMM-Newton and NuSTAR on 2016 October 20 with 23 and 123 ks exposures , respectively .
The NuSTAR hard X-ray coverage enabled us to detect the source up to 70 keV .
The 1–10 keV and 15–60 keV fluxes were 3.11 ( 3 ) \times 10 ^ { -12 } { erg s ^ { -1 } cm ^ { -2 } } and 6.8 ( 3 ) \times 10 ^ { -12 } { erg s ^ { -1 } cm ^ { -2 } } , respectively .
The 1–70 keV spectra were well fitted by a blackbody plus power-law model with a surface temperature of kT = 0.52 ( 2 ) { keV } , a photon index of the hard power-law of \Gamma = 1.21 ( 6 ) , and a column density of N _ { H } = 1.96 ( 11 ) \times 10 ^ { 22 } { cm ^ { -2 } } .
Compared with previous observations with Suzaku in 2006 and 2009 , the 1–10 keV flux showed a decrease by 25–40 % , while the spectral shape did not show any significant change with differences of kT and N _ { H } being within 10 % of each other .
Through timing analysis , we found that the rotation period of SGR 1900+14 on 2016 October 20 was 5.22669 ( 3 ) { s } .
The long-term evolution of the rotation period shows a monotonic decrease in the spin-down rate \dot { P } lasting for more than 15 years .
We also found a characteristic behavior of the hard-tail power-law component of SGR 1900+14 .
The energy-dependent pulse profiles vary in morphology with a boundary of 10 keV .
The phase-resolved spectra show the differences between photon indices ( \Gamma = 1.02 – 1.44 ) as a function of the pulse phase .
Furthermore , the photon index is positively correlated with the X-ray flux of the hard power-law component , which could not be resolved by the previous hard X-ray observations .