The first cyclotron harmonic of 4U 1538–52J. J. Rodes-Roca, J. M. Torrejón, I. Kreykenbohm, S. Martínez Núñez, A. Camero-Arranz and G. BernabéuA&A, 508 1 (2009) 395-400DOI: https://doi.org/10.1051/0004-6361/200912815
