Extremely rapid x-ray flares of tev blazars in the rxte era

TL;DR

This study systematically analyzed archival X-ray data to discover extremely rapid flares in TeV blazars, revealing sub-minute timescales and spectral properties that challenge existing models of jet emission in active galactic nuclei.

Contribution

It presents the first systematic search for sub-hour X-ray flares in TeV blazars using RXTE data, identifying the shortest AGN flare timescale and providing insights into jet inhomogeneity and emission region sizes.

Findings

PKS 2005-489 exhibits the shortest known AGN flare rise time (<0.5 min).

Flares show consistent hard spectra with photon index 1.7-1.9.

Estimated magnetic field strength in the emission region is 0.1-1.0 G.

Abstract

Rapid flares from blazars in very high energy (VHE) $\gamma$-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 $\Gamma=1.7-1.9$, and we estimate the magnetic field strength $B\sim$ 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 $\gamma$-ray flares but little synchrotron activity are less favorable.