Swift Spectroscopy of the Accretion Disk Wind in the Black Hole GRO J1655-40. (arXiv:2003.10945v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Balakrishnan_M/0/1/0/all/0/1">M. Balakrishnan</a> (1), <a href="http://arxiv.org/find/astro-ph/1/au:+Miller_J/0/1/0/all/0/1">J. M. Miller</a> (1), <a href="http://arxiv.org/find/astro-ph/1/au:+Trueba_N/0/1/0/all/0/1">N. Trueba</a> (1), <a href="http://arxiv.org/find/astro-ph/1/au:+Reynolds_M/0/1/0/all/0/1">M. Reynolds</a> (1), <a href="http://arxiv.org/find/astro-ph/1/au:+Raymond_J/0/1/0/all/0/1">J. Raymond</a> (2), <a href="http://arxiv.org/find/astro-ph/1/au:+Proga_D/0/1/0/all/0/1">D. Proga</a> (3), <a href="http://arxiv.org/find/astro-ph/1/au:+Fabian_A/0/1/0/all/0/1">A. C. Fabian</a> (4), <a href="http://arxiv.org/find/astro-ph/1/au:+Kallman_T/0/1/0/all/0/1">T. Kallman</a> (5), <a href="http://arxiv.org/find/astro-ph/1/au:+Kaastra_J/0/1/0/all/0/1">J. Kaastra</a> (6) ((1) Univ. of Michigan, (2) SAO, (3) UNLV, (4) Univ. of Cambridge, (5) NASA/GSFC, (6) SRON)
Chandra obtained two High Energy Transmission Grating (HETG) spectra of the
stellar-mass black hole GRO J1655-40 during its 2005 outburst, revealing a rich
and complex disk wind. Soon after its launch, the Neil Gehrels Swift
Observatory began monitoring the same outburst. Some X-ray Telescope (XRT)
observations were obtained in a mode that makes it impossible to remove strong
Mn calibration lines, so the Fe K-alpha line region in the spectra was
previously neglected. However, these lines enable a precise calibration of the
energy scale, facilitating studies of the absorption-dominated disk wind and
its velocity shifts. Here, we present fits to 15 Swift/XRT spectra, revealing
variability and evolution in the outflow. The data strongly point to a
magnetically driven disk wind: both the higher velocity (e.g., v ~ 10^4 km/s)
and lower velocity (e.g., v ~ 10^3 km/s) wind components are typically much
faster than is possible for thermally driven outflows (v < 200 km/s), and
photoionization modeling yields absorption radii that are two orders of
magnitude below the Compton radius that defines the typical inner extent of
thermal winds. Moreover, correlations between key wind parameters yield an
average absorption measure distribution (AMD) that is consistent with
magnetohydrodynamic wind models. We discuss our results in terms of recent
observational and theoretical studies of black hole accretion disks and
outflows, and future prospects.
Chandra obtained two High Energy Transmission Grating (HETG) spectra of the
stellar-mass black hole GRO J1655-40 during its 2005 outburst, revealing a rich
and complex disk wind. Soon after its launch, the Neil Gehrels Swift
Observatory began monitoring the same outburst. Some X-ray Telescope (XRT)
observations were obtained in a mode that makes it impossible to remove strong
Mn calibration lines, so the Fe K-alpha line region in the spectra was
previously neglected. However, these lines enable a precise calibration of the
energy scale, facilitating studies of the absorption-dominated disk wind and
its velocity shifts. Here, we present fits to 15 Swift/XRT spectra, revealing
variability and evolution in the outflow. The data strongly point to a
magnetically driven disk wind: both the higher velocity (e.g., v ~ 10^4 km/s)
and lower velocity (e.g., v ~ 10^3 km/s) wind components are typically much
faster than is possible for thermally driven outflows (v < 200 km/s), and
photoionization modeling yields absorption radii that are two orders of
magnitude below the Compton radius that defines the typical inner extent of
thermal winds. Moreover, correlations between key wind parameters yield an
average absorption measure distribution (AMD) that is consistent with
magnetohydrodynamic wind models. We discuss our results in terms of recent
observational and theoretical studies of black hole accretion disks and
outflows, and future prospects.
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