Extremely Rapid X-Ray Flares of TeV Blazars in the RXTE Era

Abstract

Rapid flares from blazars in very high-energy (VHE) γ -rays challenge the common understanding of jets of active galactic nuclei (AGNs). The same population of ultra-relativistic electrons is often thought to be responsible for both X-ray and VHE emission. We thus systematically searched for X-ray flares at sub-hour timescales of TeV blazars in the entire Rossi X-ray Timing Explorer archival database. We found rapid flares from PKS 2005−489 and S5 0716+714, and a candidate rapid flare from 1ES 1101−232. In particular, the characteristic rise timescale of PKS 2005−489 is less than half a minute, which, to our knowledge, is the shortest among known AGN flares at any wavelengths. The timescales of these rapid flares indicate that the size of the central supermassive black hole is not a hard lower limit on the physical size of the emission region of the flare. PKS 2005−489 shows possible hard lags in its flare, which could be attributed to particle acceleration (injection); its flaring component has the hardest spectrum when it first appears. For all flares, the flaring components show similar hard spectra with , and we estimate the magnetic field strength B  ∼ 0.1–1.0 G by assuming synchrotron cooling. These flares could be caused by inhomogeneity of the jets. Models that can only produce rapid γ -ray flares but little synchrotron activity are less favorable.