A NICER View of a Highly Absorbed Flare in GRS 1915+105

After 26 years of extreme outburst, the black hole X-ray binary GRS 1915+105 suddenly went dark in mid 2019, and it has remained faint ever since. This faint period, the “obscured state,” is punctuated by occasional X-ray flares, several of which were caught by NICER as part of our regular monitoring program. Spectra of one such flare exhibit strong absorption lines that provide a new look deep into the obscuring gas, revealing a clumpy, radially-stratified absorber in the outer disk. We consider several scenarios for the origin of the obscuration, including a puffed-up disk, massive winds, and the end of the long outburst. None are entirely satisfactory, but we discuss prospects for future constraints on the geometry of the mysterious absorber.