On the 110 keV Feature From A0535+26: Direct Evidence For A Near-Critical Magnetic Field

Abstract

A recent high resolution measurement of an absorption line at 110 keV in the phase-averaged spectrum of A0535+26 (Grove et al. 1994) and the conspicuous absence of a previously reported harmonic feature at around 50 keV (Kendziorra et al. 1992, 1994) are indicative of cyclotron scattering in a magnetic field of about $10^{13}$G. However, controversy has risen over whether a lower field scenario may account for the alleged absence or weakness of a lower energy fundamental harmonic feature. This work explores these two alternatives through the generation of theoretical cyclotron spectra. For lower field models, a cylindrical geometry of the line forming region and the strong angle dependence of the cross section for resonant scattering conspire to fill in a first harmonic at around 57 keV. Higher field models (B $\simeq$ 10.75 TG), however, yield significantly better fits (${\mathcal{X}}_{low}^2/{\mathcal{X}}_{high}^2\sim 71$), thus strengthening the case for a near-critical field ($B_{crit}\simeq 44$ TG). Phase-resolved OSSE spectra are not yet available but would greatly help in resolving this issue.

15 pages (AASTEX) + 2 figures (uuencoded, compressed ps), to be published in ApJ Letters, May 20, 1996

References in corpus (2)

• Elimination of resonant divergences from QED in super-strong magnetic fields
• On the 110 keV Feature From A0535+26: Direct Evidence For A Near-Critical Magnetic Field

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• Effects of the Geometry of the Line-Forming Region on the Properties of Cyclotron Resonant Scattering Lines
• Cyclotron Line Formation in a Radiation-driven Outflow
• The broad band spectral properties of binary X-ray pulsars
• Spin-polarization effects in the processes of synchrotron radiation and electron-positron pair production by a photon in a magnetic field
• On the 110 keV Feature From A0535+26: Direct Evidence For A Near-Critical Magnetic Field
• Resonant Cyclotron Radiation Transfer Model Fits to Spectra from Gamma-Ray Burst GRB870303
• Relativistic kinetic equation for Compton scattering of polarized radiation in strong magnetic field
• The broad band spectral properties of galactic X-ray binary pulsars