  In this paper, we present a unique data set of more than one year's worth of
regular observations of comet C/2013 A1(Siding Spring) with TRAPPIST in Chile,
along with low-resolution spectra obtained with the ESO/VLT FORS 2 instrument.
The comet made a close approach to Mars on October 19, 2014 and was then
observed by many space and ground-based telescopes. We followed the evolution
of the OH, NH, CN, $\mathrm{C_3}$, and $\mathrm{C_2}$ production rates as well
as the $Af\rho$ parameter as a proxy for the dust production. We detected an
outburst two weeks after perihelion, with gas and dust production rates being
multiplied by a factor five within a few days. By modelling the shape of the CN
and $\mathrm{C_2}$ radial profiles, we determined that the outburst happened
around on November 10 around 15:30 UT ($\pm$ 5h) and measured a gas ejection
velocity of $1.1\pm0.2$ km/s. We used a thermal evolution model to reproduce
the activity pattern and outburst. Our results are consistent with the
progressive formation of a dust mantle explaining the shallow dependence of gas
production rates, which may be partially blown off during the outburst. We
studied the evolution of gas composition, using various ratios such as CN/OH,
$\mathrm{C_2}$/OH, or $\mathrm{C_3}$/OH, which showed little or no variation
with heliocentric distance including at the time of the outburst. This
indicates a relative level of homogeneity of the nucleus composition.
