Multiwavelength observations of a VHE gamma-ray flare from PKS 1510−089 in 2015 (original) (raw)
Related papers
An Exceptional VHE Gamma-Ray Flare of PKS 2155-304
2007
The high-frequency peaked BL Lac PKS 2155-304 at redshift z=0.116 is a well-known VHE (>100 GeV) gamma-ray emitter. Since 2002 its VHE flux has been monitored using the H.E.S.S. stereoscopic array of imaging atmospheric-Cherenkov telescopes in Namibia. During the July 2006 dark period, the average VHE flux was measured to be more than ten times typical values observed from the object. This article focuses solely on an extreme gamma-ray outburst detected in the early hours of July 28, 2006 (MJD 53944). The average flux observed during this outburst is I(>200 GeV) = (1.72$\pm$$0.05_{\rm stat}$$\pm$$0.34_{\rm syst}$) times\timestimes 10$^{-9}$ cm$^{-2}$ s$^{-1}$, corresponding to ~7 times the flux, I(>200 GeV), observed from the Crab Nebula. Peak fluxes are measured with one-minute time scale resolution at more than twice this average value. Variability is seen up to ~600 s in the Fourier power spectrum, and well-resolved bursts varying on time scales of ~200 seconds are observed. There are no strong indications for spectral variability within the data. Assuming the emission region has a size comparable to the Schwarzschild radius of a ~10$^9 M_\odot$ black hole, Doppler factors greater than 100 are required to accommodate the observed variability time scales.
Astronomy & Astrophysics, 2009
Simultaneous HESS/CHANDRA/optical observations were performed on the BL Lac object PKS 2155-304 in the night of July 29-30 2006, when the source underwent its second major gamma-ray outburst in Summer 2006. This event took place about 44 hours after the July 28 outburst, known for its ultrafast variability. An unprecedented 6 to 8 hours of uninterrupted coverage was achieved, with spectra and light curves measured down to 7 and 2-minute timescales, respectively. The gamma-ray flux reached a maximum of 11x the Crab flux (>400 GeV), with rise/decay timescales of ~1 hour, plus a few smaller-amplitude flares superimposed on the decaying phase. The emission in the X-ray and VHE bands is strongly correlated, both in flux and spectrum, with no evidence of lags. The VHE spectrum shows a curvature that is variable with time and stronger at higher fluxes. The huge VHE variations (22x) are only accompanied by small-amplitude X-ray and optical variations (factor 2 and 15% respectively). The source has shown for the first time in an HBL a large Compton dominance (L_C/L_S ~10) -- rapidly evolving -- and a cubic relation between VHE and X-ray flux variations, during a decaying phase. These results challenge the common scenarios for the TeV-blazar emission.