INTEGRAL-detection of the ongoing outburst of the BeXRB KS 1947+300
ATel #6129; M. Kuehnel, (Remeis-Observatory & ECAP/Univ. Erlangen, Germany), C. Ferrigno, V. Esposito (ISDC/Univ. Geneva, Switzerland), V. Grinberg (MIT, USA), F. Fuerst (Caltech-SRL, USA), K. Pottschmidt (CRESST/UMBC/NASA-GSFC, USA), R. Ballhausen, I. Kreykenbohm, and J. Wilms (Remeis-Observatory & ECAP/Univ. Erlangen, Germany)
on 8 May 2014; 21:21 UT
Credential Certification: Matthias Kuehnel (firstname.lastname@example.org)
Subjects: X-ray, Binary, Neutron Star, Transient, Pulsar
The Be X-ray binary pulsar KS 1947+300 is currently showing
activity as reported by Finger et al. (ATel #6123). The source
was visible in the INTEGRAL field-of-view (MJD 56781.0 to 56783.6)
during the Cyg X-1 observation.
NuSTAR observations of the previous outburst of this source in 2013
(Fuerst et al., 2014, ApJ 784, L40) showed that its spectrum could
be described by a cut-off power-law and a cyclotron resonance
scattering feature centered at 12 keV. We used the same spectral
model and found the following best-fit parameters with their 90%
confidence intervals (chi square=31.8 with 19 dof, setting a 3%
systematic uncertainty in the data):
Gamma = 1.06(±0.12)
Efold = 31.0(±4) keV
Ecentroid = 16.7(+3.4)(-2.5) keV
Width = 2.5 keV (fixed to the NuSTAR result)
Depth = 0.191(+0.197)(-0.185).
The source flux (3-60 keV) is 1.29(+0.16)(-0.14) × 10-9 erg/s/cm2
and absorption could not be detected due to the limited spectral
range. We notice that the cyclotron line detection is marginal in
this observation, characterized by a low flux.
The time averaged folding energy Efold found in the NuSTAR data
(the source flux was between 6.49 and 9.08 × 10-9 erg/s/cm2
in the 1 to 60 keV regime) was between 22 and 24 keV, while the
photon index varied between 0.93 and 0.98. The variation of these
parameters over pulse phase was much stronger. Shortly after pulse
phase 0.2, the folding energy reached 35(±5) keV, while the photon
index increased to 1.1(±0.05). These pulse phase specific values
match the time averaged parameters we have presented above at a
much lower luminosity level.
The current activity of KS 1947+300, which seems to be weaker
than the previous outburst, might be a unique opportunity to
study any luminosity dependencies of its X-ray spectrum.