Identifying Subclasses of Long Gamma-Ray Bursts with Cumulative Light
  Curve Morphology of Prompt Emissions
  We argue a new classification scheme of long gamma-ray bursts (LGRBs) using
the morphology of the cumulative light curve of the prompt emission. We
parametrize the morphology by the absolute deviation from their constant
luminosity ($ADCL$) and derive the value for 36 LGRBs which have spectropic
redshifts, spectral parameters determined by the Band model, 1-second peak
fluxes, fluences, and 64-msec resolution light curves whose peak counts are 10
times larger than background fluctuations. Then we devide the sample according
to the value of ADCL into two groups ($ADCL < 0.17$ and $ADCL > 0.17$) and, for
each group, derive the spectral peak energy $E_{\rm p}$ - peak luminosity
$L_{\rm p}$ correlation and the Fundamental Plane of LGRBs, which is a
correlation between the spectral peak energy $E_{\rm p}$, the luminosity time
$T_{\rm L}$ ($\equiv E_{\rm iso}/L_{\rm p}$ where $E_{\rm iso}$ is isotropic
energy) and the peak luminosity $L_{\rm p}$. We find that both of the
correlations for both groups are statistically more significant compared with
ones derived from all samples. The Fundamental Planes with small and large ADCL
are given by $L_{\rm p}=10^{52.53\pm 0.01}(E_{\rm p}/10^{2.71}{\rm
keV})^{1.84\pm 0.03} (T_{\rm L}/10^{0.86}{\rm sec})^{0.29\pm0.08}$ with
$\chi^2_{\nu}=10.93/14$ and $L_{\rm p}=10^{52.98\pm0.08}(E_{\rm
p}/10^{2.71}{\rm keV})^{1.82\pm 0.09} (T_{\rm L}/10^{0.86}{\rm sec})^{0.85\pm
0.27}$ with $\chi^2_{\nu}=7.58/8$, respectively. This fact implies the
existence of subclasses of LGRBs characterized by the value of $ADCL$. Also
there is a hint for the existence of the intermediate-$ADCL$ class which
deviates from both fundamental planes. Both relations are so tight that our
result provides a new accurate distance measurement scheme up to the high
redshift universe.
