  We measure, for the first time, the median equivalent width (EW) of
H$\alpha$+[N II] in star-forming galaxies at $z\sim8$. Our estimate leverages
the unique photometric depth of the Spitzer/IRAC $5.8\mu$m-band mosaics
(probing $\approx 5500 - 7100$ A at $z\sim8$) of the GOODS Reionization Era
Wide Area Treasury from Spitzer (GREATS) program. We median stacked the stamps
of $102$ Lyman-break galaxies in the $3.6, 4.5, 5.8$ and $8.0\mu$m bands, after
carefully removing potential contamination from neighbouring sources. We infer
an extreme rest-frame EW$_0$(H$\alpha$+[N II])$=2328^{+1326}_{-1127}$ A from
the measured red $[3.6]-[5.8]=0.82\pm0.27$ mag, consistent with young
($\lesssim10^7$ yr) average stellar population ages at $z\sim8$. This implies
an ionizing photon production efficiency of
$\log(\xi_{\mathrm{ion},0}/\mathrm{erg\ Hz}^{-1})=25.97^{+0.18}_{-0.28}$. Such
a high value for photo production, similar to the highest values found at
$z\lesssim4$, indicates that only modest escape fractions
$f_\mathrm{esc}\lesssim0.3$ (at $2\sigma$) are sufficient for galaxies brighter
than $M_\mathrm{UV}<-18$ mag to re-ionize the neutral Hydrogen at $z\sim8$.
This requirement is relaxed even more to $f_\mathrm{esc}\le 0.1$ when
considering galaxies brighter than $M_\mathrm{UV}\approx -13$ mag, consistent
with recent luminosity functions and as typically assumed in studies addressing
re-ionization. These exceptional results clearly indicate that galaxies can be
the dominant source of reionizing photons, and provide us with an exciting
glimpse into what we might soon learn about the early universe, and
particularly about the Reionization Epoch, from forthcoming JWST/MIRI and
NIRCam programs.
