2013/09/27 by Mayukh Pahari, J. S. Yadav, Jérôme Rodriguez +4 · 11 citations
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysical Phenomena and Observations #Astrophysics and Star Formation Studies #Background radiation #Luminosity #Neutron star #Spectral line #Stars #astro-ph.HE
paper · pdf · doi:10.1088/0004-637x/778/1/46
published in The Astrophysical Journal 778(1), 46 (IOP Publishing) · 17 pages, 5 figures, accepted for publication in the Astrophysical Journal
arxiv created 2013/09/27 · openalex publication_date 2013/11/01 · arxiv updated 2015/06/17 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/06
We report a comprehensive study on spectral and timing properties of hard X-ray dips uniquely observed in some so-called variability classes of the micro-quasars GRS 1915+105 and IGR J17091−3624. These dips are characterized by a sudden decline in the 2.0–60.0 keV X-ray intensity by a factor of 4–12 simultaneous with the increase in hardness ratio by a factor of 2–4. Using 31 observations of GRS 1915+105 with RXTE /PCA, we show that different behaviors are observed in different types of variability classes, and we find that a dichotomy is observed between classes with abrupt transitions versus those with smoother evolution. For example, both energy-lag spectra and frequency-lag spectra of hard X-ray dips in classes with abrupt transitions and shorter dip intervals show hard-lag (hard photons lag soft photons), while both lag spectra during hard dips in classes with smoother evolution and longer dip intervals show soft-lag. Both lag time-scales are of the order of 100–600 mS. We also show that timing and spectral properties of hard X-ray dips observed in light curves of IGR J17091−3624 during its 2011 outburst are consistent with the properties of the abrupt transitions in GRS 1915+105 rather than smooth evolutions. A global correlation between the X-ray intensity cycle time and hard dip time is observed for both abrupt and smooth transition which may be due to two distinct physical processes whose time-scales are eventually correlated. We discuss implications of our results in the light of some generic models.