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Multiple Cyclotron Lines in V0332+53

ATel #381; W. Coburn (SSL/UCB), P. Kretschmar (MPE/ISDC), I. Kreykenbohm (IAAT/ISDC), V. A. McBride (Southampton University), R. E. Rothschild (CASS/UCSD), J. Wilms (Warwick)
on 6 Jan 2005; 21:37 UT
Credential Certification: Wayne Coburn (wcoburn@ssl.berkeley.edu)

Subjects: X-ray, Gamma Ray, Binary, Neutron Star, Transient, Pulsar

Referred to by ATel #: 382

As part of our continuing RXTE observing campaign of V0332+53 in outburst (ATEL #372, #371, #349), we obtained 63ks of good exposure time between 2004 December 24-26. We measured a 2-10keV flux of 2.6E-8 ergs/cm2/s with the PCA. In our RXTE spectrum, once a standard pulsar continua is fit there are clear, line-like residuals at ~25 and ~50keV. This is not surprising since Makishima et al. (1990, ApJ 356 59L) first reported a 28.5keV cyclotron line in the source using observations obtained with Ginga. Fitting with Gaussian-shaped absorption lines, we find a pair of features with energies (26.34+/-0.03)keV and (49.1+/-0.2)keV. However, the fundamental is poorly fit with a simple Gaussian, or even pair of Gaussian, and there is evidence in the residuals for considerable non-Gaussian shaped structure at that energy. Since this residual structure was dominating the fits, we looked at the HEXTE-only spectra above 35keV and found another line-like feature at (74+/2)keV. This makes V0332+53 the only accreting pulsar other than 4U0115+63 to exhibit more than two cyclotron lines.