We report on a Chandra /HETG X-ray spectrum of the black hole candidate MAXI J1305 - 704 .
A rich absorption complex is detected in the Fe L band , including density–sensitive lines from Fe XX , XXI , and XXII .
Spectral analysis over three bands with photoionization models generally requires a gas density of n \geq 10 ^ { 17 } ~ { } { cm } ^ { -3 } .
Assuming a luminosity of L = 10 ^ { 37 } ~ { } { erg } ~ { } { s } ^ { -1 } , fits to the 10–14 Å band constrain the absorbing gas to lie within r = 3.9 \pm 0.7 \times 10 ^ { 3 } km from the central engine , or about r = 520 \pm 90 ~ { } ( M / 5 ~ { } M _ { \odot } ) ~ { } r _ { g } , where r _ { g } = GM / c ^ { 2 } .
At this distance from the compact object , gas in Keplerian orbits should have a gravitational red-shift of z = v / c \simeq 3 \pm 1 \times 10 ^ { -3 } ~ { } ( M / 5 ~ { } M _ { \odot } ) , and any tenuous inflowing gas should have a free–fall velocity of v / c \simeq 6 \pm 1 \times 10 ^ { -2 } ~ { } ( M / 5 ~ { } M _ { \odot } ) ^ { 1 / 2 } .
The best-fit single-zone photoionization models measure a red-shift of v / c = 2.6 - 3.2 \times 10 ^ { -3 } .
Models with two zones provide significantly improved fits ; the additional zone is measured to have a red-shift of v / c = 4.6–4.9 \times 10 ^ { -2 } ( models including two zones suggest slightly different radii and may point to lower densities ) .
Thus , the shifts are broadly consistent with the photoionization radius .
The results may be explained in terms of a ‘ ‘ failed wind ’ ’ like those predicted in some numerical simulations .
We discuss our results in the context of accretion flows across the mass scale , and the potential role of failed winds in black hole state transitions .