Chandra high-resolution spectra of 4U~1630-47: the disappearance of the wind

TL;DR

This study analyzes high-resolution X-ray spectra of the black hole binary 4U 1630-47, revealing wind disappearance during state transitions and suggesting thermal pressure as the wind's launching mechanism.

Contribution

First detailed high-resolution spectral analysis of 4U 1630-47 across different accretion states, linking wind presence to accretion states and exploring wind launching mechanisms.

Findings

Wind detected in soft states with blueshifted absorption lines.

Wind absent in intermediate/hard states, indicating state-dependent wind behavior.

Thermal pressure likely drives wind in soft states, with possible wind exhaustion or acceleration in state transitions.

Abstract

We present the analysis of six {\it Chandra} X-ray high-resolution observations of the black hole low-mass X-ray binary 4U~1630-47 taken during its 2012-2013 outburst. {\rm Fe}~{\sc XXVI} K$\alpha$, K$\beta$, {\rm Fe}~{\sc XXV} K$\alpha$, K$\beta$ and {\rm Ca}~{\sc XX} K$\alpha$ blueshifted absorption lines were identified in the first four observations, which correspond to soft accretion states. The remaining observations, associated to intermediate and possibly hard accretion states, do not show significant absorption features down to equivalent width of 1 eV for both {\rm Fe}~{\sc XXVI} and {\rm Fe}~{\sc XXV}. We inferred wind launching radii between $1.2- 2.0$ ($10^{12}$ cm$/n$)$ \times 10^{11}$~cm and column densities $N({\rm H})> 10^{23}$ cm$^{-2}$. In the first four observations we found that thermal pressure is likely to be the dominant launching mechanism for the wind, although such conclusions depend on the assumed density. We used the spectral energy distributions obtained from our continuum modeling to compute thermal stability curves for all observations using the {\sc xstar} photoionization code. We found that the absence of lines in the transitional state cannot be attributed to an evolution of the plasma caused by thermal instabilities derived from the change in the continuum spectrum. In contrast, the disappearance of the wind could indicate an acceleration of the flow or that the plasma has been exhausted during the soft state.