1998/03/26 by S. Campana, L. Stella, S. Mereghetti +7 · 4 citations
Earth and Planetary Sciences · Engineering · Physics and Astronomy · #Astrophysical Phenomena and Observations #Geophysics and Sensor Technology #High-pressure geophysics and materials #astro-ph
paper · pdf · doi:10.1086/311357
4 pages (1 figure + 2 tables). Accepted for publication in ApJLetters. Requires emulateapj.sty and timesfonts.sty (included)
arxiv created 1998/03/26 · openalex publication_date 1998/05/20 · arxiv updated 2009/12/01 · openalex created_date 2020/11/23 · openalex updated_date 2026/08/01
We report on the 1997 March-April BeppoSAX observations of Aquila X-1, which were the first to monitor the evolution of the spectral and time-variability properties of a neutron star soft X-ray transient from the outburst decay to quiescence. We observed a fast X-ray flux decay, which brought the source luminosity from ~10 36 to ~10 33 ergs s -1 in less than 10 days. The X-ray spectrum showed a power-law high-energy tail with a photon index Γ~2, which hardened to Γ~1-1.5 as the source reached quiescence. These observations, together with the detection by the Rossi X-Ray Timing Explorer of a periodicity of a few milliseconds during an X-ray burst, likely indicate that the rapid flux decay is caused by the onset of the propeller effect, which arises from the very fast rotation of the neutron star magnetosphere. The X-ray luminosity and hard spectrum that characterize the quiescent emission can be consistently interpreted as shock emission by a turned-on rotation-powered pulsar.