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4U 0115+63 Observations with RXTE

ATel #337; W. Coburn, E. Kalemci (UCB); P. Kretschmar (MPE/ISDC); I. Kreykenbohm (IAAT/ISDC); R. Rothschild (UCSD); R. Staubert (IAAT); J. Wilms (Warwick)
on 1 Oct 2004; 21:30 UT
Credential Certification: Wayne Coburn (wcoburn@ssl.berkeley.edu)

Subjects: X-ray, Binary, Neutron Star

On MJD 53270.382 we observed the source 4U 0115+63 during outburst for ~20 ks with RXTE. The 2-10 keV flux during the observation was (6.75 +/- 0.06)x10**-9 ergs cm**-2 s**-1. Our preliminary analysis of the joint PCA/HEXTE phase averaged spectrum indicates the presence of the known ~12 keV cyclotron line, along with upwards of 4 approximately harmonically spaced higher harmonics. This is similar to what was seen in the 1999 outburst. There is also a clear QPO in the lightcurve, with individual cycles varying from the average by as much as 45%. The QPO in the power spectrum peaks at ~4.5 mHz, with a ~1 mHz FWHM. This is similar to the ~2 mHz QPO observed in this source in 1999, and a mHz frequency QPO is probably a ubiquitous feature of this source during outburst.