Observations of Mrk 421 with INTEGRAL.
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G. G. Lichti, V. Beckmann, C. Boisson, J. Buckley,P. Charlot, W. Collmar, B. Degrange, A. Djannati-Atai,J. Finley, G. Fossati, G. Henri, K. Katarzynski, D. Kieda, K. Mannheim, A. Marcowith, M. Punch, A. Saggione,L. Saugé, V. Schönfelder, A. Sillanpaa, D. Smith,H. Sol, F. Tavecchio, L. Takalo, M. Tornikoski,A. von Kienlin, T. Weekes
An accepted ToO Proposal for multiwavelength observations(829 ks)
Points in red are >3σ detections!
Shortest variability time scale: 2.9 hours size of emission region
δ = Doppler factor ( 10)z = 0.031 (redshift)c = speed of light
l < 3 · 1015 cm = 203 AU
for Θ 0° β > 0.98
X-ray & TeV flares occurred simul-taneously to within 1.5 hours
BeppoSAX observationsLightcurves at X-Ray & TeV Energies
Flare at TeV and X-ray energiesnearly coincident same electron population respon-sible for X-ray and γ-ray radiation?
from Maraschi et al., Ap. J. 526, L81, 1999
of RXTE: 2-60 keVCorrelation between X-ray and TeV γ-ray lightcurves(after Blazejowski et al., Ap. J. 630, 130, 2005)
X-ray and TeV γ-ray intensitycorrelate, yet only loosely!
However:The X-rays lag behind the TeV γ-rays in contradiction to the SSC model!
ASCA data show:
soft X-rays (0.5-2 keV)lag the X-rays from2-7.5 keV
Interpretation:radiative cooling of e-!
However reality of thesetime lags questioned!
from Takahashi et al.,Ap. J. 470, L89, 1996
decay phaseEvolution of the X-Ray Photon Indices
Higher fluxes haveflatter (harder) spectra!
The evolution of the spectrumis dictated by the interplay of acceleration, cooling and con-finement times. The clockwiseevolution is consistent withstochastic Fermi accelerationand synchrotron cooling.
F = A·E-n·exp(-E/Ecut)A = 0.28 ± 0.02n = 1.91 ± 0.03
Ecut = (98 ± 16) keV
For a spectrum with exponential cut off theemission-maximum energy Ep is given by:
Ep = (2 – n) • Ecut
Inserting the values from above one obtains: Ep = (8.8 3.3) keV
This is an averaged value over the whole observation.It is the highest peak energy ever measured for Mrk 421!
Ep correlates nicely with the bolometric energy (BeppoSAX data from Massaro et al., Ap. J. 413, 489, 2004):
Total bolometric luminosity:~1045 erg/s
Neither the spectra at X-ray nor at TeV energies can be fitted with a simple power law complexer spectral shapes have to be used
X-ray data of BeppoSAX(Massaro et al., A&A 413, 489, 2004)
TeV data(Aharonian et al., A&A 350, 757, 1999)
Krennrich et al. (Ap. J. 560, L45, 2001) performed fits to TeV dataof Mrk 421 with different analytical functions:
Power laws do not fit the spectra very well: χ2red = 41
χ2red = 6.3
The TeV data of Mrk 421can be well fitted by apower law with an expo-nential cut off!
χ2red = 2.8
χ2red = 3.0
However at X-rays a power law with exponential cut off doesnot fit the data well! Fossati et al. (Ap. J. 541, 166, 2000) used a continuous combination of 2 power laws:
m & n are thepower-law indices forE >> E0 and E << E0, respectively.
Since this model has 5 parameters which cannot simply be re-lated to physical quantities a log-parabolic function was used:
Fixing the energy E0 at a useful energy(in the middle of the considered energyrange) this function has only 3 parameters.
Calculation of the peak energy ofthespectral energy density νFν
The spectral energydensity at Ep:
The log-parabolic function can be analyticallyintegrated leading to the bolometric luminosity:
Limitation of the function: restricted to symmetric distributions!
Assumption:p = probability of a particle to gain an energy ε in an acceleration step iγi = ε · γi-1 = ε · ε · γi-2 = · · · · · · = εi · γo (ε > 1 & independent of energy)Ni = p · Ni-1 = p · p · Ni-2 = · · · = pi · No (p < 1 & independent of energy)
Eliminating i yields:
g, q > 0 andconstant
Assumption: p depends on energy:
The probability for particle acceleration decreases with increasing energy!
Using γi = ε · γi-1 one obtains:
It can be shown analytically thata and b are linearly correlated.This is supported by BeppoSAX data!(Massaro et al., A&A 413, 489, 2004)
Most synchrotron spectra of BL lacs are curved (due to radiativelosses and escape of high-energy electrons from emitting region).
0.41 1.31 4.14 TeV
13.1 TeVAbsorption of TeV γ-rays atintergalactic photon field
300 GeV – 20 TeV γ-rays interact mostefficiently with IR photons (1 – 50 µm)via γTeV + γIR e+ e-