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We present visible and near-infrared photometric and spectroscopicobservations of interstellar object 2I/Borisov taken from 2019 September 10 to2019 November 29 using the GROWTH, the APO ARC 3.5 m and the NASA/IRTF 3.0 mcombined with post and pre-discovery observations of 2I obtained by ZTF from2019 March 17 to 2019 May 5. Comparison with imaging of distant Solar Systemcomets shows an object very similar to mildly active Solar System comets withan out-gassing rate of $\sim$10$^{27}$ mol/sec. The photometry, taken infilters spanning the visible and NIR range shows a gradual brightening trend of$\sim0.03$ mags/day since 2019 September 10 UTC for a reddish object becomingneutral in the NIR. The lightcurve from recent and pre-discovery data reveals abrightness trend suggesting the recent onset of significant H$_2$O sublimationwith the comet being active with super volatiles such as CO at heliocentricdistances $>$6 au consistent with its extended morphology. Using the advancedcapability to significantly reduce the scattered light from the coma enabled byhigh-resolution NIR images from Keck adaptive optics taken on 2019 October 04,we estimate a diameter of 2I's nucleus of $\lesssim$1.4 km. We use the sizeestimates of 1I/'Oumuamua and 2I/Borisov to roughly estimate the slope of theISO size-distribution resulting in a slope of $\sim$3.4$\pm$1.2, similar toSolar System comets and bodies produced from collisional equilibrium.

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Characterization of the Nucleus, Morphology and Activity of Interstellar  Comet 2I/Borisov by Optical and Near-Infrared GROWTH, Apache Point, IRTF, ZTF  and Keck Observations