  We present the results of a detailed investigation of the prompt and
afterglow emission in the HESS detected GRB 190829A. Swift and Fermi
observations of the prompt phase of this GRB reveal two isolated sub-bursts or
episodes, separated by a quiescent phase. The energetic and the spectral
properties of the first episode are in stark contrast to the second. The first
episode, which has a higher spectral peak of $\sim 120\:\text{keV}$ and a low
isotropic energy $\sim 10^{50}\:\text{erg}$ is an outlier to the Amati
correlation and marginally satisfies the Yonetoku correlation. However, the
energetically dominant second episode has lower peak energy and is consistent
with the above correlations. We compared this GRB to other low luminosity GRBs
(LLGRBs). Prompt emission of LLGRBs also indicates a relativistic shock
breakout origin of the radiation. For GRB 190829A, some of the properties of a
shock breakout origin are satisfied. However, the absence of an accompanying
thermal component and energy above the shock breakout critical limit precludes
a shock breakout origin. In the afterglow, an unusual long-lasting late time
flare of duration $\sim 10^4\:\text{s}$ is observed. We also analyzed the
late-time \fermi-LAT emission that encapsulates the H.E.S.S. detection. Some of
the LAT photons are likely to be associated with the source. All the above
observational facts suggest GRB 190829A is a peculiar low luminosity GRB that
is not powered by a shock breakout, and with an unusual rebrightening due to a
patchy emission or a refreshed shock during the afterglow. Furthermore, our
results show that TeV energy photons seem common in both high luminosity GRBs
and LLGRBs.
