NuSTAR and Swift detection of a ~600 s QPO in 4U 0115+63
ATel #8231; R. Ballhausen, I. Kreykenbohm, M. Kuehnel, D. Hertel, J. Wilms (Remeis-Observatory & ECAP/Univ. Erlangen-Nuremberg, Germany), K. Pottschmidt, D. M. Marcu-Cheatham (CRESST/UMBC/NASA-GSFC, USA), F. Fuerst(SRL/Caltech, USA), P. Kretschmar (ESA/ESAC, Madrid, Spain), J. A. Tomsick (SSL/Univ. of California, Berkeley, USA), C. Ferrigno (ISDC, Univ. Geneva, Switzerland), A. Camero-Arranz (IEEC-CSIC, Spain), R. E. Rothschild, P. B. Hemphill (UC San Diego, USA), M. T. Wolff (NRL, USA), D. Klochkov (IAAT, Germany)
on 30 Oct 2015; 22:18 UT
Credential Certification: Ingo Kreykenbohm (Ingo.Kreykenbohm@sternwarte.uni-erlangen.de)
Subjects: X-ray, Binary, Neutron Star, Transient
Referred to by ATel #: 15967
The recurrent Be X-ray binary pulsar 4U 0115+63 is
currently in outburst (ATel #8179). After having reached a peak flux
of ~500 mCrab in the 15-50 keV Swift/BAT band during the peak, the
source is now declining with some flaring activity. NuSTAR observed
the source on 2015 October 22 during the peak of the outburst for ~15
ks. The mean dead-time corrected 3-79 keV NuSTAR count rate was ~350
cts/s per module. In addition to the NuSTAR observation, four 2 ks
Swift snapshots have been performed since 2015 October 21.
The NuSTAR and all Swift lightcurves show a quasi periodic variation
of the count rate by a factor of about 3 on a timescale of ~600 s. We
interpret this variation as the 2 mHz Quasi Periodic Oscillation (QPO)
already observed in this source by Heindl et al. (1999, ApJ, 521, L49)
with RXTE during the 1999 outburst.
4U 0115+63 is known to exhibit five cyclotron lines (Santangelo et
al. 1999, ApJ, 523, L85; Heindl et al. 2000, AIP Conf. Proc., 510,
173). The preliminary NuSTAR spectrum also clearly shows the
signatures of multiple cyclotron lines.
A second NuSTAR observation is scheduled during the declining phase
together with two further Swift snapshot observations.
