  The presence of a magnetic field can have a strong impact on the evolution of
a binary star. However, only a dozen of magnetic OB binaries are known as of
today and available to study this effect, including very few magnetic pulsating
spectroscopic OB binaries. We aim at checking for the presence of a magnetic
field in the B5IV hierarchical triple system HD 1976 with spectropolarimetric
data obtained with Narval at the Bernard Lyot Telescope (TBL). We use orbital
parameters of HD 1976 available in the literature to disentangle the Narval
intensity spectra. We compute Stokes V profiles with the Least Square
Deconvolution (LSD) technique to search for magnetic signatures. We then derive
an estimate of the longitudinal magnetic field strength for each observation
and for various line lists. Our disentangling of the intensity spectra shows
that HD 1976 is a double-lined spectroscopic (SB2) binary, with the lines of
the secondary component about twice broader than the ones of the primary
component. We do not identify the third component. Moreover, we find that clear
magnetic signatures are present in the spectropolarimetric measurements of HD
1976 and seem to be associated with the primary component. We conclude that HD
1976 is a magnetic slowly-pulsating double-lined spectroscopic binary star,
with an undetected third component. It is the second such example known (with
HD 25558).
