Signatures of synchrotron emission and of electron acceleration   in the X-ray spectra
of Mrk 421

Tramacere, A.; Massaro, F.; Cavaliere, A.

doi:10.1051/0004-6361:20066723

Cited by 126 publications

(194 citation statements)

References 28 publications

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“…In particular, Kardashev (1962) showed that a log-parabolic spectrum results from a Fokker-Planck equation with a momentum-diffusion term and a monoenergetic or quasi-monoenergetic particle injection. The results presented in Tramacere et al (2007b) rely on the theoretical prediction from the Kardashev (1962) that the curvature term (r) is inversely proportional to the diffusion term (D):…”

Section: E P -B Trendmentioning

confidence: 84%

“…Its flux variations go along with significant spectral variations (Fossati et al 2000a;Massaro et al 2004) and the spectral shape in general exhibits a curvature that is described well by a logparabolic model (Massaro et al 2004;Tramacere et al 2007b).…”

Section: Introductionmentioning

confidence: 98%

“…Stawarz & Petrosian (2008) showed that a distribution with similar spectral properties can be obtained as a steady-state energy spectra of particles undergoing momentum diffusion due to resonant interactions with turbulent MHD modes. Tramacere et al (2007b) suggested that the connection between the X-ray curvature and the emitting particles, and its evolution with the source state, could be investigated in testing the prediction of the scenarios listed above. In particular, both stochastic (Kardashev 1962) and energy-dependent acceleration mechanisms predict an anticorrelation between the curvature and the SED peak energy (E p ).…”

Section: Introductionmentioning

confidence: 99%

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Swift observations of the very intense flaring activity of Mrk 421 during 2006. I. Phenomenological picture of electron acceleration and predictions for MeV/GeV emission

Tramacere¹,

Giommi

Perri

et al. 2009

A&A

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276

295

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Aims. We present the results of a deep spectral analysis of all Swift observations of Mrk 421 between April 2006 and July 2006, when it reached its highest X-ray flux recorded until the end of 2006. The peak flux was about 85 milli-Crab in the 2.0-10.0 keV band, and the peak energy (E p ) of the spectral energy distribution (SED) was often at energies higher than 10 keV. We study trends between the spectral parameters, and the physical insights the parameters provide into the underlying acceleration and emission mechanisms. Methods. We performed a spectral analysis of Swift observations to investigate trends between the spectral parameters. We searched for acceleration and energetic features phenomenologically linked to the SSC model parameters, by predicting their effects in the γ-ray band, and in particular, the spectral shape expected in the Fermi Gamma-ray Space Telescope-LAT band. Results. We confirm that the X-ray spectrum is described well by a log-parabolic distribution close to E p , that the peak flux of the SED (S p ) is correlated with E p , and that E p is anti-correlated with the curvature parameter (b). The spectral evolution in the Hardness-ratio-flux plane shows both clockwise and counter-clockwise patterns. During the most energetic flares, the UV-to-soft-X-ray spectral shape requires an electron distribution spectral index of s 2.3. Conclusions. We demonstrate that the UV-to-X-ray emission from Mrk 421 is probably generated by a population of electrons that is actually curved, and has a low energy power-law tail. The observed spectral curvature is consistent with both stochastic acceleration or energy-dependent acceleration probability mechanisms, whereas the power-law slope of XRT-UVOT data is close to that inferred from the GRBs X-ray afterglow and in agreement with the universal first-order relativistic shock acceleration models. This scenario implies that magnetic turbulence may play a twofold role: spatial diffusion relevant to the first order process and momentum diffusion relevant to the second order process.

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Section: E P -B Trendmentioning

confidence: 84%

Section: Introductionmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

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Swift observations of the very intense flaring activity of Mrk 421 during 2006. I. Phenomenological picture of electron acceleration and predictions for MeV/GeV emission

Tramacere¹,

Giommi

Perri

et al. 2009

A&A

Self Cite

276

295

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“…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).…”

Section: Introductionmentioning

confidence: 99%

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

Baloković¹,

Paneque²,

Madejski³

et al. 2016

ApJ

113

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We present coordinated multiwavelength observations of the bright, nearby BL Lacertae object Mrk 421 taken in 2013 January-March, involving GASP-WEBT, Swift, NuSTAR, Fermi-LAT, MAGIC, VERITAS, and other collaborations and instruments, providing data from radio to very high energy(VHE) γ-ray bands. NuSTAR yielded previously unattainable sensitivity in the 3-79keV range, revealing that the spectrum softens when the source is dimmer until the X-ray spectral shape saturates into a steep 3 G » power law, with no evidence for an exponential cutoff or additional hard components up to ∼80keV. For the first time, we observed both the synchrotron and the inverse-Compton peaks of the spectral energy distribution (SED) simultaneously shifted to frequencies below the typical quiescent state by an order of magnitude. The fractional variability as a function of photon energy shows a double-bump structure that relates to the two bumps of the broadband SED. In each bump, the variability increases with energy, which, in the framework of the synchrotron self-Compton model, implies that the electrons with higher energies are more variable. The measured multi band variability, the significant X-ray-to-VHE correlation down to some of the lowest fluxes ever observed in both bands, the lack of correlation between optical/UV and X-ray flux, the low degree of polarization and its significant (random) variations, the short estimated electron cooling time, and the significantly longer variability timescale observed in the NuSTAR light curves point toward in situ electron acceleration and suggest that there are multiple compact regions contributing to the broadband emission of Mrk 421 during low-activity states.

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“…Landau et al 1986;Massaro et al 2004;Chen et al 2014) and such curved spectra of blazars are known to arise due to log parabolic electron distributions (e.g. Tramacere et al 2007Tramacere et al ,2009Paggi et al 2009). …”

Section: Introductionmentioning

confidence: 99%

Signature of inverse Compton emission from blazars

Gaur

Mohan

Wierzcholska

et al. 2017

Monthly Notices of the Royal Astronomical Society

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Blazars are classified into high, intermediate and low energy peaked sources based on the location of their synchrotron peak. This lies in infra-red/optical to ultra-violet bands for low and intermediate peaked blazars. The transition from synchrotron to inverse Compton emission falls in the X-ray bands for such sources. We present the spectral and timing analysis of 14 low and intermediate energy peaked blazars observed with XMMNewton spanning 31 epochs. Parametric fits to X-ray spectra helps constrain the possible location of transition from the high energy end of the synchrotron to the low energy end of the inverse Compton emission. In seven sources in our sample, we infer such a transition and constrain the break energy in the range 0.6 10 keV. The Lomb-Scargle periodogram is used to estimate the power spectral density (PSD) shape. It is well described by a power law in a majority of light curves, the index being flatter compared to general expectation from AGN, ranging here between 0.01 and 1.12, possibly due to short observation durations resulting in an absence of long term trends. A toy model involving synchrotron self-Compton (SSC) and external Compton (EC; disk, broad line region, torus) mechanisms are used to estimate magnetic field strength 0.03 -0.88 G in sources displaying the energy break and infer a prominent EC contribution. The timescale for variability being shorter than synchrotron cooling implies steeper PSD slopes which are inferred in these sources.

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Signatures of synchrotron emission and of electron acceleration in the X-ray spectra of Mrk 421

Cited by 126 publications

References 28 publications

Swift observations of the very intense flaring activity of Mrk 421 during 2006. I. Phenomenological picture of electron acceleration and predictions for MeV/GeV emission

Swift observations of the very intense flaring activity of Mrk 421 during 2006. I. Phenomenological picture of electron acceleration and predictions for MeV/GeV emission

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

Signature of inverse Compton emission from blazars

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