  The optical counterpart of the neutron star X-ray binary and well known X-ray
burster, 4U 1636-53 (= 4U 1636-536 = V801 Ara) has been well studied for three
decades. However to date, no infrared studies have been reported. Our aims are
to identify and investigate the near-infrared (NIR) counterpart of 4U 1636-53.
We present deep, K_s-band (2.2 micron) imaging of the region of 4U 1636-53
taken with the Infrared Spectrometer And Array Camera (ISAAC) on the Very Large
Telescope. Archival optical and UV data are used to infer the 0.2-2.2 micron
spectral energy distribution (SED). One star is located at coordinates alpha
=16:40:55.57, delta =-53:45:05.2 (J2000; 1 sigma positional uncertainty of ~
0.3 arcsec) which is consistent with the known optical position of 4U 1636-53;
its magnitude is K_s = 16.14 +- 0.12. This star is also detected in the 2MASS
survey in J-band and has a magnitude of J = 16.65 +- 0.22. Under the assumption
that the persistent emission is largely unvarying, the 0.4-2.2 micron
de-reddened SED can be described by a power law; F_nu propto nu^(1.5 +- 0.3),
with some possible curvature (F_nu propto nu^(<= 1.5)) at 0.2-0.4 microns. The
SED can be approximated by a blackbody of temperature ~ 27 000 K. This is
typical for an active low-mass X-ray binary, and the emission can be explained
by the outer regions of a (likely irradiated) accretion disc. We therefore
interpret this K_s-band star as the NIR counterpart.
