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Title: Properties of unique hard X-ray dips observed from GRS 1915+105 and IGR J17091–3624 and their implications

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-raymore » 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.« less
Authors:
; ;  [1] ;  [2] ;  [3] ;  [4]
  1. Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai (India)
  2. Laboratoire AIM, CEA/IRFU-CNRS/INSU-Université Paris Diderot, CEA DSM/IRFU/SAp, F-91191 Gif-sur-Yvette (France)
  3. Inter University Center for Astronomy and Astrophysics, Pune (India)
  4. Pt. Ravishankar Sukla University, Raipur, Chattishgarh (India)
Publication Date:
OSTI Identifier:
22342010
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 778; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACCRETION DISKS; BLACK HOLES; COMPUTERIZED SIMULATION; CORRELATIONS; EVOLUTION; GESELLSCHAFT FUER ANLAGEN- UND REAKTORSICHERHEIT; HARD X RADIATION; HARDNESS; KEV RANGE; PHOTONS; POLAR-CAP ABSORPTION; QUASARS; SPECTRA; VISIBLE RADIATION