  We calculate the electromagnetic (EM) decay widths of the $B^{\pm}_c(2S)$
meson, which is observed recently by the ATLAS Collaboration. The main EM decay
channels of this particle are $1{^3S_1}\gamma$ and $1{P}\gamma$, which, in
literature, are estimated to have the branching ratio of about $1/10$. In this
work, we get the partial decay widths: $\Gamma(2{^1S_0}\rightarrow
1{^3S_1}\gamma)=0.192$ keV, $\Gamma(2{^1S_0}\rightarrow 1{P_1}\gamma) = 2.24$
keV and $\Gamma(2{^1S_0}\rightarrow 1{P_1^\prime}\gamma) = 11.4$ keV. In the
calculation, the instantaneous approximated Bethe-Salpeter method is used. For
the $P$-wave $B_c$ mesons, the wave functions are given by mixing the $^3P_1$
and $^1P_1$ states. Within the Mandelstam formalism, the decay amplitude is
given, which includes the relativistic corrections.
