STATISTICS OF X-RAY FLARES OF SAGITTARIUS A?: EVIDENCE FOR SOLAR-LIKE SELF-ORGANIZED CRITICALITY PHENOMENA

摘要

X-ray flares have routinely been observed from the supermassive black hole?at our Galactic center, Sagittarius A (Sgr A). The nature of these flares remains largely unclear, despite many theoretical models. In this paper, we study the statistical properties of the Sgr A X-ray flares by fitting the count rate (CR) distribution and the structure function of the light curve with a Markov Chain Monte Carlo method. With the 3-million-second Chandra observations accumulated in the Sgr A X-ray Visionary Project, we construct the theoretical light curves through Monte Carlo simulations. We find that the 2–8 keV X-ray light curve can be decomposed into a quiescent component with a constant CR of count s?1 and a flare component with a power-law fluence distribution with . The duration–fluence correlation can also be modeled as a power law with (95% confidence). These statistical properties are consistent with the theoretical prediction of the self-organized criticality system with the spatial dimension S = 3. We suggest that the X-ray flares represent plasmoid ejections driven by magnetic reconnection (similar to solar flares) in the accretion flow onto the black hole.