  (Abridged) Palomar Gattini-IR is a new wide-field, near-infrared robotic time
domain survey operating at Palomar Observatory. Using a 30 cm telescope mounted
with a H2RG detector, Gattini-IR achieves a field of view of 25 sq. deg. with a
pixel scale of 8.7" in J-band. Here, we describe the system design, survey
operations, data processing system and on-sky performance of Palomar
Gattini-IR. As a part of the nominal survey, Gattini-IR scans $\approx 7500$
square degrees of the sky every night to a median 5$\sigma$ depth of $15.7$ AB
mag outside the Galactic plane. The survey covers $\approx 15000$ square
degrees of the sky visible from Palomar with a median cadence of 2 days. A
real-time data processing system produces stacked science images from dithered
raw images taken on sky, together with PSF-fit source catalogs and transient
candidates identified from subtractions within a median delay of $\approx 4$
hours from the time of observation. The calibrated data products achieve an
astrometric accuracy (RMS) of $\approx 0.7$" with respect to Gaia DR2 for
sources with S/N $> 10$, and better than $\approx 0.35$" for sources brighter
than $\approx 12$ Vega mag. The photometric accuracy (RMS) achieved in the
PSF-fit source catalogs is better than $\approx 3$% for sources brighter than
$\approx 12$ Vega mag, as calibrated against the 2MASS catalog. With a field of
view $\approx 40\times$ larger than any other existing near infrared imaging
instrument, Gattini-IR is probing the reddest and dustiest transients in the
local universe such as dust obscured supernovae in nearby galaxies, novae
behind large columns of extinction within the galaxy, reddened micro-lensing
events in the Galactic plane and variability from cool and dust obscured stars.
We present results from transients and variables identified since the start of
the commissioning period.
