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  1. OA@INAF
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  3. 1 CONTRIBUTI IN RIVISTE (Journal articles)
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Please use this identifier to cite or link to this item: http://hdl.handle.net/20.500.12386/28760
Title: A variable-frequency HFQPO in GRS 1915+105 as observed with AstroSat
Authors: BELLONI, Tomaso Maria Melchiorre 
Bhattacharya, Dipankar
Caccese, Pietro
Bhalerao, Varun
Vadawale, Santosh
Yadav, J. S.
Issue Date: 2019
Journal: MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 
Number: 489
Issue: 1
First Page: 1037
Abstract: From the analysis of more than 92 ks of data obtained with the Large Area X-Ray Proportional Counter (LAXPC) instrument onboard AstroSat we have detected a clear high-frequency quasi-periodic oscillation (HFQPO) whose frequency varies between 67.4 and 72.3 Hz. In the classification of variability classes of GRS 1915+105, at the start of the observation period the source was in class ω and at the end the variability was that of class μ: both classes are characterized by the absence of hard intervals and correspond to disc-dominated spectra. After normalization to take into account time variations of the spectral properties as measured by X-ray hardness, the QPO centroid frequency is observed to vary along the hardness-intensity diagram, increasing with hardness. We also measure phase lags that indicate that HFQPO variability at high energies lags that at lower energies and detect systematic variations with the position on the hardness-intensity diagram. This is the first time that (small) variations of the HFQPO frequency and lags are observed to correlate with other properties of the source. We discuss the results in the framework of existing models, although the small (7 per cent) variability observed is too small to draw firm conclusions.
URI: http://hdl.handle.net/20.500.12386/28760
URL: https://academic.oup.com/mnras/article-abstract/489/1/1037/5543950?redirectedFrom=fulltext
ISSN: 0035-8711
DOI: 10.1093/mnras/stz2143
Bibcode ADS: 2019MNRAS.489.1037B
Fulltext: open
Appears in Collections:1.01 Articoli in rivista

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