XRF 100316D/SN 2010bh: CLUE TO THE DIVERSE ORIGIN OF NEARBY SUPERNOVA-ASSOCIATED GAMMA-RAY BURSTS

X-ray Flash (XRF) 100316D, a nearby super-long underluminous burst with a peak energy Ep ∼ 20 keV, was detected by Swift and was found to be associated with an energetic supernova SN 2010bh. Both the spectral and the temporal behavior are rather similar to XRF 060218, except that the latter was associated with a 'less energetic' SN 2006aj and had a prominent soft thermal emission component in the spectrum. We analyze the spectral and temporal properties of this burst and interpret the prompt gamma-ray emission and the early X-ray plateau emission as synchrotron emission from a dissipating Poynting flux dominated outflow, probably powered by a magnetar with a spin period of P ∼ 10 ms and the polar cap magnetic field Bp ∼ 3 x 1015 G. The energetic supernova SN 2010bh associated with this burst is, however, difficult to interpret within the slow magnetar model, and we suspect that the nascent magnetar may spin much faster with an initial rotation period ∼1 ms. It suggests a delay between the core collapse and the emergence of the relativistic magnetar wind from the star. The diverse behaviors of low-luminosity gamma-ray bursts and their associated supernovae may be understood within a unified picture that invokes different initial powers of the central engine and different delay times between the core collapse and the emergence of the relativistic jet from the star.