Relativistic Reflection and Reverberation in GX 339–4 with NICER and NuSTAR
Name
Wang_2020_ApJ_899_44.pdf
Description
Published version
Size
1.77 MB
Format
Adobe PDF
Checksum (MD5)
2b69771a3e5df69a2f3dfb3753217c76
Author(s)
Wang, Jingyi
Kara, Erin
Steiner, James F
García, Javier A
Homan, Jeroen
Neilsen, Joseph
Marcel, Grégoire
Ludlam, Renee M
Tombesi, Francesco
Cackett, Edward M
Date Issued
2020
Journal
Astrophysical Journal
Publisher
American Astronomical Society
Version
Final published version
Abstract
© 2020. The American Astronomical Society. All rights reserved.. We analyze seven Neutron Star Interior Composition Interior Explorer (NICER) and Nuclear Spectroscopic Telescope Array epochs of the black hole X-ray binary GX 339-4 in the hard state during its two most recent hard-only outbursts in 2017 and 2019. These observations cover the 1-100 keV unabsorbed luminosities between 0.3% and 2.1% of the Eddington limit. With NICER's negligible pileup, high count rate, and unprecedented time resolution, we perform a spectral-timing analysis and spectral modeling using relativistic and distant reflection models. Our spectral fitting shows that as the inner disk radius moves inward, the thermal disk emission increases in flux and temperature, the disk becomes more highly ionized, and the reflection fraction increases. This coincides with the inner disk increasing its radiative efficiency around ∼1% Eddington. We see a hint of the hysteresis effect at ∼0.3% of Eddington; the inner radius is significantly truncated during the rise (>49R g ), while only a mild truncation (∼5R g ) is found during the decay. At higher frequencies (2-7 Hz) in the highest-luminosity epoch, a soft lag is present whose energy dependence reveals a thermal reverberation lag with an amplitude similar to previous findings for this source. We also discuss the plausibility of the hysteresis effect and the debate of the disk truncation problem in the hard state.
MIT Department
MIT Kavli Institute for Astrophysics and Space Research
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DOI of Published Version
https://doi.org/10.3847/1538-4357/ab9ec3
