Pursuing the Amplitude of Tensor Mode Power Spectrum in Light of BICEP2

In this brief report, we try to constrain general parameterized forms of scalar and tensor mode power spectra, $P_{s}(k)\equiv A_s(k/k_0)^{n_s-1+\frac{1}{2}\alpha_s\ln(k/k_0)}$ and $P_{t}(k)\equiv A_t(k/k_0)^{n_t+\frac{1}{2}\alpha_t\ln(k/k_0)}$ by the recently released BICEP2 data set plus {\it Planck} 2013, WMAP9 and BAO. We loosen the inflationary consistence relations, and take $A_s$, $n_s$, $A_t$ and $n_t$ as free model parameters, via the Markov chain Monte Carlo method, the interested model parameter space was investigated, we obtained marginalized $68\%$ limits on the interested parameters are: $n_s=0.96339_{-0.00554}^{+0.00560}$, $n_t=1.70490_{-0.56979}^{+0.56104}$, ${\rm{ln}}(10^{10} A_s)=3.08682_{-0.02614}^{+0.02353}$ and ${\rm{ln}}(10^{10} A_t)=3.98376_{-0.54885}^{+0.86045}$. The ratio of the amplitude at the scale $k=0.002 \text{Mpc} ^{-1}$ is $r=0.01655_{-0.01655}^{+0.00011}$ which is consistent with the {\it Planck} 2013 result.