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Title: AstroSat /LAXPC Observation of Cygnus X-1 in the Hard State

Abstract

We report the first analysis of data from AstroSat /LAXPC observations of Cygnus X-1 in 2016 January. LAXPC spectra reveals that the source was in the canonical hard state, represented by a prominent thermal Comptonization component having a photon index of ∼1.8 and high temperature of kT{sub e} > 60 keV along with weak reflection and possible disk emission. The power spectrum can be characterized by two broad lorentzian functions centered at ∼0.4 and ∼3 Hz. The rms of the low-frequency component decreases from ∼15% at around 4 keV to ∼10% at around 50 keV, while that of the high-frequency one varies less rapidly from ∼13.5% to ∼11.5% in the same energy range. The time lag between the hard (20–40 keV) and soft (5–10 keV) bands varies in a step-like manner being nearly constant at ∼50 milliseconds from 0.3 to 0.9 Hz, decreasing to ∼8 milliseconds from 2 to 5 Hz and finally dropping to ∼2 milliseconds for higher frequencies. The time lags increase with energy for both the low and high-frequency components. The event mode LAXPC data allows for flux resolved spectral analysis on a timescale of 1 s, which clearly shows that the photon index increased from ∼1.72more » to ∼1.80 as the flux increased by nearly a factor of two. We discuss the results in the framework of the fluctuation propagation model.« less

Authors:
;  [1]; ; ; ; ; ; ; ;  [2];  [3];  [4];  [5]
  1. Inter-University Centre for Astronomy and Astrophysics, Pune 411007 (India)
  2. Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai (India)
  3. UM-DAE Center of Excellence for Basic Sciences, University of Mumbai, Kalina, Mumbai-400098 (India)
  4. University of Mumbai, Kalina, Mumbai-400098 (India)
  5. Dept. of Astronomy and Astrophysics, Raman Research Institute, Bengaluru-560080 (India)
Publication Date:
OSTI Identifier:
22663885
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 835; Journal Issue: 2; 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; DATA ANALYSIS; EMISSION; FLUCTUATIONS; KEV RANGE; PHOTONS; REFLECTION; SPACE VEHICLES; SPECTRA; WAVE PROPAGATION; X RADIATION

Citation Formats

Misra, Ranjeev, Pahari, Mayukh, Yadav, J S, Chauhan, Jai Verdhan, Antia, H M, Chitnis, V R, Dedhia, Dhiraj, Katoch, Tilak, Madhwani, P., Shah, Parag, Agrawal, P C, Manchanda, R K, and Paul, B, E-mail: rmisra@iucaa.in. AstroSat /LAXPC Observation of Cygnus X-1 in the Hard State. United States: N. p., 2017. Web. doi:10.3847/1538-4357/835/2/195.
Misra, Ranjeev, Pahari, Mayukh, Yadav, J S, Chauhan, Jai Verdhan, Antia, H M, Chitnis, V R, Dedhia, Dhiraj, Katoch, Tilak, Madhwani, P., Shah, Parag, Agrawal, P C, Manchanda, R K, & Paul, B, E-mail: rmisra@iucaa.in. AstroSat /LAXPC Observation of Cygnus X-1 in the Hard State. United States. doi:10.3847/1538-4357/835/2/195.
Misra, Ranjeev, Pahari, Mayukh, Yadav, J S, Chauhan, Jai Verdhan, Antia, H M, Chitnis, V R, Dedhia, Dhiraj, Katoch, Tilak, Madhwani, P., Shah, Parag, Agrawal, P C, Manchanda, R K, and Paul, B, E-mail: rmisra@iucaa.in. Wed . "AstroSat /LAXPC Observation of Cygnus X-1 in the Hard State". United States. doi:10.3847/1538-4357/835/2/195.
@article{osti_22663885,
title = {AstroSat /LAXPC Observation of Cygnus X-1 in the Hard State},
author = {Misra, Ranjeev and Pahari, Mayukh and Yadav, J S and Chauhan, Jai Verdhan and Antia, H M and Chitnis, V R and Dedhia, Dhiraj and Katoch, Tilak and Madhwani, P. and Shah, Parag and Agrawal, P C and Manchanda, R K and Paul, B, E-mail: rmisra@iucaa.in},
abstractNote = {We report the first analysis of data from AstroSat /LAXPC observations of Cygnus X-1 in 2016 January. LAXPC spectra reveals that the source was in the canonical hard state, represented by a prominent thermal Comptonization component having a photon index of ∼1.8 and high temperature of kT{sub e} > 60 keV along with weak reflection and possible disk emission. The power spectrum can be characterized by two broad lorentzian functions centered at ∼0.4 and ∼3 Hz. The rms of the low-frequency component decreases from ∼15% at around 4 keV to ∼10% at around 50 keV, while that of the high-frequency one varies less rapidly from ∼13.5% to ∼11.5% in the same energy range. The time lag between the hard (20–40 keV) and soft (5–10 keV) bands varies in a step-like manner being nearly constant at ∼50 milliseconds from 0.3 to 0.9 Hz, decreasing to ∼8 milliseconds from 2 to 5 Hz and finally dropping to ∼2 milliseconds for higher frequencies. The time lags increase with energy for both the low and high-frequency components. The event mode LAXPC data allows for flux resolved spectral analysis on a timescale of 1 s, which clearly shows that the photon index increased from ∼1.72 to ∼1.80 as the flux increased by nearly a factor of two. We discuss the results in the framework of the fluctuation propagation model.},
doi = {10.3847/1538-4357/835/2/195},
journal = {Astrophysical Journal},
number = 2,
volume = 835,
place = {United States},
year = {Wed Feb 01 00:00:00 EST 2017},
month = {Wed Feb 01 00:00:00 EST 2017}
}