  This paper presents the multi-wavelength analysis of a 13 s quasi-periodic
pulsation (QPP) observed in hard X-ray (12-300 keV) and microwave (4.9-34 GHz)
emissions during a C-class flare occurred on 21 September 2015. AIA 304 and 171
\AA~ images show an emerging loop/flux tube (L1) moving radially outward, which
interacts with preexisting structures within the active region. The QPP was
observed during the expansion and rising motion of L1. The Nobeyama
Radioheliograph (NoRH) microwave images in 17/34 GHz channels reveal a single
radio source, which was co-spatial with a neighboring loop (L2). In addition,
using AIA 304 \AA~ images, we detected intensity oscillations in the legs of
loop L2 with a period of about 26 s. A similar oscillation period was observed
in the GOES soft X-ray flux derivative. This oscillation period seems to
increase with time. We suggest that the observed QPP is most likely generated
by the interaction between loops L2 and L3 observed in the AIA hot channels
(131 and 94 \AA). The merging speed of loops L2 and L3 was ~35 km/s. Loop L1
destroyed possibly by its interaction with preexisting structures in the active
region and produced a cool jet with the speed ~106-118 km/s associated with a
narrow CME (~770 km/s). Another mechanism of the QPP in terms of a sausage
oscillation of the loop (L2) is also possible.
