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A recent high resolution measurement of an absorption line at 110 keV in thephase-averaged spectrum of A0535+26 (Grove et al. 1994) and the conspicuousabsence of a previously reported harmonic feature at around 50 keV (Kendziorraet al. 1992, 1994) are indicative of cyclotron scattering in a magnetic fieldof about $10^{13}$G. However, controversy has risen over whether a lower fieldscenario may account for the alleged absence or weakness of a lower energyfundamental harmonic feature. This work explores these two alternatives throughthe generation of theoretical cyclotron spectra. For lower field models, acylindrical geometry of the line forming region and the strong angle dependenceof the cross section for resonant scattering conspire to fill in a firstharmonic at around 57 keV. Higher field models (B $\simeq$ 10.75 TG), however,yield significantly better fits (${\cal X}^2_{low}/{\cal X}^2_{high} \sim 71$),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 helpin resolving this issue.Comment: 15 pages (AASTEX) + 2 figures (uuencoded, compressed ps), to be  published in ApJ Letters, May 20, 199

On the 110 keV Feature from A0535+26: Direct Evidence for a Near-critical Magnetic Field