* Astronomy

Blobrana · L

RE: Scorpius X-1

Blobrana · L

Scorpius X-1 was discovered on the 19th June, 1962, by a team under Riccardo Giacconi at American Science and Engineering in Cambridge, Massachusetts, who launched an X-ray detector on an Aerobee 150 sounding rocket to look for X-ray emissions from Earth's moon. Instead, Scorpius X-1 became the first X-ray source discovered outside the Solar System.
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Blobrana · L

Title: INTEGRAL observations of Sco X-1: evidence for Comptonisation up to 200 keV
Authors: T. Maiolino, F. D'Amico, J. Braga

We have analysed a long-term database for Sco X-1 obtained with the telescope IBIS onboard the INTEGRAL satellite in order to study the hard X-ray behaviour of Sco X-1 from 20 up to 200 keV. Besides the data used for producing of the INTEGRAL catalogue of sources, this is the longest (412 ks) database of IBIS on Sco X-1 up to date. The production of hard X-ray tails in low-mass X-ray binaries is still a matter of debate. Since most of the fits to the high-energy part of the spectra are done with powerlaw models, the physical mechanism for the hard X-ray tail production is unclear. The purpose of this study is to better constrain those possible mechanisms. Our main result shows a strong correlation between the fluxes in the thermal and nonthermal part of Sco X-1 spectra. We thus suggest that Comptonisation of lower energy photons is the mechanism for producing hard X-ray tails in Sco X-1.

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Blobrana · L

Title: Energy dependence of NBO in Scorpius X-1
Authors: J. Wang, H.-K. Chang, C.-Y. Liu

We report the energy dependence of normal branch oscillations (NBOs) in Scorpius X-1, a low-mass X-ray binary (LMXB) Z-source. Three characteristic quantities (centroid frequency, quality factor and fractional root-mean-squared (rms) amplitude) of a QPO signal as functions of photon energy are investigated. We found that the NBO centroid frequency decreases with increasing photon energy when it is below 6-8 keV and turns positively correlated with photon energy at the higher-energy side. The rms amplitude increases significantly with the photon energy below 13 keV, and then flats out in the energy band of 13-20 keV. There is no clear dependence on photon energy for the quality factor. Based on these results, we suggest that the NBO originates mainly from the transition layer.

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Blobrana · L

An Aerobee 150 rocket launched on June 12, 1962, detected the first X-rays from another celestial source (Scorpius X-1) at J1950 RA 16h 15m Dec -15.2°. Sco X-1 is a LMXB in which the visual counterpart is V818 Scorpii.
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Blobrana · L

Title: The Orbital Period of Scorpius X-1
Authors: Robert I. Hynes, Christopher T. Britt (Louisiana State University)

The orbital period of Sco X-1 was first identified by Gottlieb et al. (1975). While this has been confirmed on multiple occasions, this work, based on nearly a century of photographic data, has remained the reference in defining the system ephemeris ever since. It was, however, called into question when Vanderlinde et al. (2003) claimed to find the one-year alias of the historical period in RXTE/ASM data and suggested that this was the true period rather than that of Gottlieb et al. (1975). We examine data from the All Sky Automated Survey (ASAS) spanning 2001-2009. We confirm that the period of Gottlieb et al. (1975) is in fact the correct one, at least in the optical, with the one-year alias strongly rejected by these data. We also provide a modern time of minimum light based on the ASAS data.

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