A new X-ray outburst from the Be X-ray binary Swift J1626.6-5156 was recently detected by MAXI/GSC (ATel #14454).
On 2021 March 11 16:40, NICER obtained a 2.75 ks exposure of the
source. The results of the pulsation search show that there is a strong
periodicity of 15.34 seconds. The 0.5 - 10 keV pulse profile has a
sinusoidal shape with a 34% pulsed fraction. Since the detected pulse
period is consistent with previous observations (e.g, ATel #678, #679),
we confirm that this is a new outburst from Swift J1626.6-5156 after 15
years of quiescence. The NICER 0.5-10 keV spectrum can be fitted with
an absorbed blackbody model (kT = 0.093±0.005 keV; hydrogen column
density 1.08±0.08×1022 cm-2) plus a broken
power-law continuum with pre and post photon indices 0.45(±0.09) and
1.27 (±0.07), respectively. The best-fit break energy is at 3.4(±0.1)
keV. A cyclotron absorption line is possibly detected; the best-fit
centroid energy is 9.1 (+0.3, -0.2) keV and the line width is 1.1(+0.3,
-0.2) keV with an optical depth of 0.5(+0.3, -0.2). The X-ray flux in
the 0.5-10 keV band is 3.18(±0.04)×10-10 erg cm-2 s-1.
The obtained centroid energy of the cyclotron absorption line is
consistent with that detected in the previous outburst (DeCesar et al.
2013, ApJ, 762, 61). However, since the energy range of NICER is limited
to about 12 keV, we encourage follow-up observations in the higher
energy range to reveal the information about the cyclotron resonance
NICER is a 0.2-12 keV X-ray telescope operating on the International
Space Station. The NICER mission and portions of the NICER science team
activities are funded by NASA.