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We present near-infrared (NIR) time-series spectroscopy, as well ascomplementary ultraviolet (UV), optical, and NIR data, of the Type Ia supernova(SN Ia) iPTF13ebh, which was discovered within two days from the estimated timeof explosion. The first NIR spectrum was taken merely 2.3 days after explosionand may be the earliest NIR spectrum yet obtained of a SN Ia. The most strikingfeatures in the spectrum are several NIR C I lines, and the C I {\lambda}1.0693{\mu}m line is the strongest ever observed in a SN Ia. Interestingly, no strongoptical C II counterparts were found, even though the optical spectroscopictime series began early and is densely-cadenced. Except at the very earlyepochs, within a few days from the time of explosion, we show that the strongNIR C I compared to the weaker optical C II appears to be general in SNe Ia.iPTF13ebh is a fast decliner with {\Delta}m15(B) = 1.79 $\pm$ 0.01, and itsabsolute magnitude obeys the linear part of the width-luminosity relation. Itis therefore categorized as a "transitional" event, on the fast-declining endof normal SNe Ia as opposed to subluminous/91bg-like objects. iPTF13ebh showsNIR spectroscopic properties that are distinct from both the normal andsubluminous/91bg-like classes, bridging the observed characteristics of the twoclasses. These NIR observations suggest composition and density of the innercore similar to that of 91bg-like events, and a deep reaching carbon burninglayer not observed in slower declining SNe Ia. There is also a substantialdifference between the explosion times inferred from the early-time light curveand the velocity evolution of the Si II {\lambda}0.6355 {\mu}m line, implying along dark phase of ~ 4 days.

Strong near-infrared carbon in the Type Ia supernova iPTF13ebh