21 research outputs found
Cross-spectral analysis of the X-ray variability of Mrk 421
Using the cross-spectral method, we confirm the existence of the X-ray hard
lags discovered with cross-correlation function technique during a large flare
of Mrk 421 observed with BeppoSAX . For the 0.1--2 versus 2--10keV light
curves, both methods suggest sub-hour hard lags. In the time domain, the degree
of hard lag, i.e., the amplitude of the 3.2--10 keV photons lagging the lower
energy ones, tends to increase with the decreasing energy. In the Fourier
frequency domain, by investigating the cross-spectra of the 0.1--2/2--10 keV
and the 2--3.2/3.2--10 keV pairs of light curves, the flare also shows hard
lags at the lowest frequencies. However, with the present data, it is
impossible to constrain the dependence of the lags on frequencies even though
the detailed simulations demonstrate that the hard lags at the lowest
frequencies probed by the flare are not an artifact of sparse sampling, Poisson
and red noise. As a possible interpretation, the implication of the hard lags
is discussed in the context of the interplay between the (diffusive)
acceleration and synchrotron cooling of relativistic electrons responsible for
the observed X-ray emission. The energy-dependent hard lags are in agreement
with the expectation of an energy-dependent acceleration timescale. The
inferred magnetic field (B ~ 0.11 Gauss) is consistent with the value inferred
from the Spectral Energy Distributions of the source. Future investigations
with higher quality data that whether or not the time lags are
energy-/frequency-dependent will provide a new constraint on the current models
of the TeV blazars.Comment: 11 pages, 6 figures, accepted by MNRA
Three dimensional imaging of short pulses
We exploit a slightly noncollinear second-harmonic cross-correlation scheme
to map the 3D space-time intensity distribution of an unknown complex-shaped
ultrashort optical pulse. We show the capability of the technique to
reconstruct both the amplitude and the phase of the field through the coherence
of the nonlinear interaction down to a resolution of 10 m in space and 200
fs in time. This implies that the concept of second-harmonic holography can be
employed down to the sub-ps time scale, and used to discuss the features of the
technique in terms of the reconstructed fields.Comment: 16 pages, 6 figure
SYLOS lasers - the frontier of few-cycle, multi-TW, kHz lasers for ultrafast applications at extreme light infrastructure attosecond light pulse source
Nonlinear space-time dynamics of ultrashort wave packets in water
We have monitored the space\u2013time transformation of a 150-fs pulse undergoing self-focusing and filamentation in water, by means of the nonlinear gating technique. We have observed that pulse splitting and subsequent recombination apply to axial temporal intensity only, whereas the space-integrated pulse profile preserves its original shape