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Properties of Unique Hard X-Ray Dips Observed from GRS 1915+105 and IGR J17091-3624 and Their Implications

Abstract : 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.
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Submitted on : Sunday, March 27, 2022 - 10:34:52 AM
Last modification on : Tuesday, March 29, 2022 - 3:28:43 AM

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Mayukh Pahari, J. S. Yadav, Jérôme Rodriguez, Ranjeev Misra, Sudip Bhattacharyya, et al.. Properties of Unique Hard X-Ray Dips Observed from GRS 1915+105 and IGR J17091-3624 and Their Implications. The Astrophysical Journal, 2013, 778, ⟨10.1088/0004-637X/778/1/46⟩. ⟨insu-03620882⟩

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