  After 26 years in outburst, the black hole X-ray binary GRS 1915+105 dimmed
considerably in early 2018; its flux dropped sharply in mid-2019, and it has
remained faint ever since. This faint period, the "obscured state," is
punctuated by occasional X-ray flares, many of which have been observed by
NICER as part of our regular monitoring program. Here we present detailed
time-resolved spectroscopy of one bright flare, whose spectrum shows evidence
of high column density partial covering absorption and extremely deep
absorption lines (equivalent widths over 100 eV in some cases). We study the
time-dependent ionization of the obscuring gas with XSTAR, ultimately
attributing the absorption to a radially-stratified absorber of density
1e12-1e13 cm^-3 at a ~few x 1e11 cm from the black hole. We argue that a
vertically-extended outer disk could explain this obscuration. We discuss
several scenarios to explain the obscured state, including massive outflows, an
increase in the mass accretion rate, and changes in the outer disk that herald
the approach of quiescence, but none are entirely satisfactory. Alternative
explanations, such as obscuration by the accretion stream impact point, may be
testable with current or future data.
