2000/07/18 by D. K. Galloway, Galloway, D. K.
Engineering · Physics and Astronomy · #Astrophysical Phenomena and Observations #Astrophysics (astro-ph) #FOS: Physical sciences #Superconducting Materials and Applications #astro-ph
paper · pdf · doi:10.48550/arxiv.astro-ph/0007274
22 pages, 6 figures, submitted to ApJ
arxiv created 2000/07/18 · openalex publication_date 2000/07/18 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
X-ray observations of the binary pulsar GX 1+4 made using the Rossi X-ray Timing Explorer (RXTE) satellite between February 1996 and May 1997 were analysed to quantify source spectral variation with luminosity. Mean Proportional Counter Array (PCA) spectra over the range 2-40 keV are best fitted with a Comptonization model, with source spectrum temperature T0 approx 1-1.3 keV, plasma temperature Te approx 6-10 keV, and optical depth tau approx 2-6. The range of fitted T0 was consistent with the source spectrum originating at the neutron star polar cap, with Compton scattering taking place primarily in the hot plasma of the accretion column. Both the fitted optical depth and plasma temperature vary significantly with the source flux. The variation of the optical depth (and hence the density of the scattering region) with luminosity strongly suggests increasing cross-sectional area of the accretion column at higher accretion rate Mdot. The wide range of source luminosity spanned by archival observations of GX 1+4 offers evidence for two distinct spectral states above and below LX approx 2*1037 erg/s (2-60 keV, assuming a source distance of 10 kpc). GX 1+4 additionally exhibits dramatic hourly variations in neutral column density nH indicative of density variations in the stellar wind from the giant companion.