In this paper we give a brief review of our recent studies on the long and short gamma-ray bursts (GRBs) detected Swift, in an effort to understand the puzzle of classifying GRBs. We consider that it is still an appealing conjecture that both long an
d short GRBs are drawn from the same parent sample by observational biases.
A nearby super-luminous burst GRB 130427A was simultaneously detected by six $gamma$-ray space telescopes ({it Swift}, Fermi-GBM/LAT, Konus-Wind, SPI-ACS/INTEGRAL, AGILE and RHESSI) and by three RAPTOR full-sky persistent monitors. The isotropic $gam
ma-$ray energy release is of $sim 10^{54}$ erg, rendering it the most powerful explosion among the GRBs with a redshift $zleq 0.5$. The emission above 100 MeV lasted about one day and four photons are at energies greater than 40 GeV. We show that the count rate of 100 MeV-100 GeV emission may be mainly accounted for by the forward shock synchrotron radiation and the inverse Compton radiation likely dominates at GeV-TeV energies. In particular, an inverse Compton radiation origin is established for the $sim (95.3,~47.3,~41.4,~38.5,~32)$ GeV photons arriving at $tsim (243,~256.3,~610.6,~3409.8,~34366.2)$ s after the trigger of Fermi-GBM. Interestingly, the external-inverse-Compton-scattering of the prompt emission (the second episode, i.e., $tsim 120-260$ s) by the forward-shock-accelerated electrons is expected to produce a few $gamma-$rays at energies above 10 GeV, while five were detected in the same time interval. A possible unified model for the prompt soft $gamma-$ray, optical and GeV emission of GRB 130427A, GRB 080319B and GRB 090902B is outlined. Implication of the null detection of $>1$ TeV neutrinos from GRB 130427A by IceCube is discussed.
Sw 1644+57/GRB 110328A is a remarkable cosmological X-ray outburst detected by the {it Swift} satellite. Its early-time ($tlesssim 0.1$ days since the trigger) X-ray emission resembles some gamma-ray bursts (GRBs), e.g., GRB 090417B. But the late-tim
e flaring X-ray plateau lasting $> 40$ days renders it unique. We examine the possibilities that the outburst is a super-long GRB powered either by the fallback accretion onto a nascent black hole or by a millisecond pulsar, and find out that these two scenarios can address some but not all of the main observational features. We then focus on the model of tidal disruption of a (giant) star by a massive black hole. The mass of the tidal-disrupted star is estimated to be $gtrsim$ a few solar masses. A simple/straightforward argument for a magnetic origin of the relativistic outflow is presented.
