Constraints on Dark Energy from New Observations including Pan-STARRS
  In this paper, we set the new limits on the equation of state parameter (EoS)
of dark energy with the observations of cosmic microwave background radiation
(CMB) from Planck satellite, the type Ia supernovae from Pan-STARRS and the
baryon acoustic oscillation (BAO). We consider two parametrization forms of
EoS: a constant $w$ and time evolving $w(a)=w_0+w_a(1-a)$. The results show
that with a constant EoS, $w=-1.141\pm{0.075}$ ($68\%~C.L.$), which is
consistent with $\Lambda$CDM at about $2\sigma$ confidence level. For a time
evolving $w(a)$ model, we get $w_0=-1.09^{+0.16}_{-0.18}$ ($1\sigma~C.L.$),
$w_a=-0.34^{+0.87}_{-0.51}$ ($1\sigma~C.L.$), and in this case $\Lambda$CDM can
be comparable with our observational data at $1\sigma$ confidence level. In
order to do the parametrization independent analysis, additionally we adopt the
so called principal component analysis (PCA) method, in which we divide
redshift range into several bins and assume $w$ as a constant in each redshift
bin (bin-w). In such bin-w scenario, we find that for most of the bins
cosmological constant can be comparable with the data, however, there exists
few bins which give $w$ deviating from $\Lambda$CDM at more than $2\sigma$
confidence level, which shows a weak hint for the time evolving behavior of
dark energy. To further confirm this hint, we need more data with higher
precision.
