During hard X-ray observations of the Norma spiral arm region by the Nuclear Spectroscopic Telescope Array ( NuSTAR ) in 2013 February , a new transient source , NuSTAR J163433–4738.7 , was detected at a significance level of 8- \sigma in the 3–10 keV bandpass .
The source is consistent with having a constant NuSTAR count rate over a period of 40 ks and is also detected simultaneously by Swift at lower significance .
The source is not significantly detected by NuSTAR , Swift , or Chandra in the days before or weeks after the discovery of the transient , indicating that the strong X-ray activity lasted for between \sim 0.5 and 1.5 days .
Near-IR imaging observations were carried out before and after the X-ray activity , but we are not able to identify the counterpart .
The combined NuSTAR and Swift energy spectrum is consistent with a power-law with a photon index of \Gamma = 4.1 ^ { +1.5 } _ { -1.0 } ( 90 % confidence errors ) , a blackbody with kT = 1.2 \pm 0.3 keV , or a bremsstrahlung model with kT = 3.0 ^ { +2.1 } _ { -1.2 } keV .
The reduced- \chi ^ { 2 } values for the three models are not significantly different , ranging from 1.23 to 1.44 for 8 degrees of freedom .
The spectrum is strongly absorbed with N _ { H } = ( 2.8 ^ { +2.3 } _ { -1.4 } ) \times 10 ^ { 23 } cm ^ { -2 } , ( 9 ^ { +15 } _ { -7 } ) \times 10 ^ { 22 } cm ^ { -2 } , and ( 1.7 ^ { +1.7 } _ { -0.9 } ) \times 10 ^ { 23 } cm ^ { -2 } , for the power-law , blackbody , and bremsstrahlung models , respectively .
Although the high column density could be due to material local to the source , it is consistent with absorption from interstellar material along the line of sight at a distance of 11 kpc , which would indicate an X-ray luminosity > 10 ^ { 34 } erg s ^ { -1 } .
Although we do not reach a definitive determination of the nature of NuSTAR J163433–4738.7 , we suggest that it may be an unusually bright active binary or a magnetar .