Observing Mkn 421 with XMM-Newton: The EPIC–PN point of view

Abstract

Abstract. We present three observations (four exposures) of Mkn 421 performed by XMM-Newton in November and December 2002, concentrating on the EPIC-PN camera data. The X-ray spectra were soft and steepened toward high energies. The source was highly variable and the hardness ratio plots displayed a clear harder-when-stronger correlation. During two complete flares the source showed strong spectral evolution: a hardness ratio and a time resolved spectral analysis revealed both clockwise and counterclockwise rotating loop patterns, suggesting the presence of temporal lags between different energy band variations. We confirmed this result and estimated the delay with a cross-correlation analysis performed on the single flares, discussing also variability patterns that could reproduce the asymmetry seen in the cross-correlation function. We verified our findings by reproducing the two flares with analytical models. We obtained consistent results: during one flare, Mkn 421 displayed soft lags, while in the other case it showed hard lags. In both cases, the delay increases with the energy difference between the light curves. Finally, we discuss the presence and the frequency dependence of the temporal lags as an effect of particle acceleration, cooling and escape timescales, showing that our data are consistent with this picture.

MULTIWAVELENGTH STUDY OF QUIESCENT STATES OF Mrk 421 WITH UNPRECEDENTED HARD X-RAY COVERAGE PROVIDED BY NuSTAR IN 2013

“…Although the observed range of hardness ratios is relatively large at any specific count rate, the overall trend is clearly present in the binned data shown with thick black lines. There are no apparent circular patterns observed in the count rate versus hardness ratio plane, as previously seen in soft X-ray observations during bright flaring periods (e.g., Takahashi et al 1996;Ravasio et al 2004;Tramacere et al 2009). We note, however, that the circular patterns might not be observable in the NuSTAR data presented here simply …”

“…Mrk 421 and other HBL-type blazars have been extensively studied in the soft X-ray band (e.g., Makino et al 1987;Takahashi et al 1996;Ravasio et al 2004;Tramacere et al 2007bTramacere et al , 2009, revealing a range of spectral slopes in various quiescent and flaring states. Less is known about the hard X-ray (10 keV) properties of blazar jet emission: the data are far fewer and available mostly for flaring episodes, or averaged over relatively long timescales (e.g., Guainazzi et al 1999;Giebels et al 2007;Fossati et al 2008;Ushio et al 2009;Abdo et al 2011).…”

Simultaneous multiwavelength observations of the second exceptionalγ-ray flare of PKS 2155–304 in July 2006

“…This algorithm requires a continuous light curve without interruptions, therefore the few gaps were filled with the running mean value calculated over the 8 closest bins (e.g., Ravasio et al 2004). The results are fully consistent with the DCF analysis, indicating that the small gaps in the VHE light curves -the X-ray light curve is continuous -do not introduce significant distortions for such well sampled data.…”

“…It is indicative of a slow acceleration/injection process, whose timescale is comparable with the other timescales of the system (t acc ≈ t cool ). The information about the flare then propagates from lower to higher energies as particles are gradually accelerated (Kirk et al 1998;Ravasio et al 2004). If the optical variations are indeed associated with the flaring zone, the optical data would support this scenario as well, exhibiting increasing flux just before the X-ray rise at the end of the Chandra observation.…”

Internal shocks in relativistic outflows: collisions of magnetized shells

“…Ravasio et al (2004) pointed out that the asymmetry can be reproduced by modeling light curves as initially rising 6 The absolute scale of B depends on ρ ext (Sect. 2).…”