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We present new optical and {\it Chandra} observations of the field containingthe ultraluminous X-ray source NGC 1313 X-2. On an ESO 3.6 m image, the {\itChandra} error box embraces a $R=21.6$ point-like object and excludes apreviously proposed optical counterpart. The resulting X-ray/optical flux ratioof NGC 1313 X-2 is $\sim 500$. The value of $f_X/f_{opt}$, the X-rayvariability history and the spectral distribution derived from a re-analysis ofthe {\it ROSAT}, {\it ASCA} and {\it XMM} data indicate a luminous X-ray binaryin NGC 1313 as a likely explanation for NGC 1313 X-2. If the X-ray softcomponent observed in the {\it XMM} EPIC spectrum originates from an accretiondisk, the inferred mass of the compact remnant is $\approx 100 M_\odot$, makingit an intermediate mass black hole. The derived optical luminosity ($L\approx10^5 L_\odot$) is consistent with that of a $\approx 15-20 M_\odot$ companion.The properties of the environment of NGC 1313 X-2 are briefly discussed.Comment: 12 pages, 6 figures; submitted to The Astrophysical Journa

The Ultraluminous X‐Ray Source NGC 1313 X‐2 (MS 0317.7−6647) and Its Environment