scholarly journals The First- and Second-Order Fermi Acceleration Processes in BL Lacertae Objects

Galaxies ◽  
2018 ◽  
Vol 6 (4) ◽  
pp. 125
Author(s):  
Bidzina Kapanadze
Keyword(s):  
Shock Front ◽  
High Energy ◽  
Second Order ◽  
X Rays ◽  
Fermi Acceleration ◽  
Bl Lacertae Objects ◽  
Component Structure ◽  
Stochastic Acceleration ◽  
First Order ◽  
Bl Lacertae

BL Lacertae objects constitute a rare class of active galactic nuclei with extreme observational features attributed to the Doppler-boosted emission from a relativistic jet, closely aligned to our line-of-sight. Their spectral energy distribution, extending over 17–19 orders of frequency from radio to the TeV energy range, is of non-thermal origin and shows a typical two-component structure. The lower-energy component, ranging from the radio to X-rays in the high-energy peaked BL Lacertae sources, is widely accepted to be a synchrotron radiation emitted by ultra-relativistic charged particles, to be initially accelerated via the Blandford–Znajek mechanism or magneto-hydrodynamic processes in the vicinity of the central super-massive black hole. However, the accelerated particles should lose the energy, sufficient for the emission of the keV-GeV photons, very quickly and the source can maintain its flaring state on the daily-weekly timescales only if some additional acceleration mechanisms are continuously at work. According to different studies and simulations,the particles can gain tremendous energies due to the propagation of relativistic shocks through the jet: By means of first-order Fermi mechanism at the shock front, or they undergo an efficient stochastic (second-order Fermi) acceleration close to the shock front, in the turbulent jet medium. Our intensive X-ray spectral study of TeV-detected, bright BL Lacertae objects (Mrk 421, 1ES 1959+650, Mrk 501) often show the signatures of the stochastic acceleration, while those related to the first-order Fermi process arefound relatively rarely. The TeV-undetected sources (1H 1516+660, BZB J1341+3959, BZB J1237+6258) mostly do not show the signatures of the efficient stochastic acceleration in their jets.

scholarly journals BL Lacertae Objects: A Short Review

2019 ◽  
pp. 121-142
Author(s):  
B. Kapanadze
Keyword(s):  
Spectral Energy Distribution ◽  
High Energy ◽  
Second Order ◽  
X Rays ◽  
Fermi Acceleration ◽  
Energy Component ◽  
Bl Lacertae Objects ◽  
Stochastic Acceleration ◽  
X Ray ◽  
Bl Lacertae

BL Lacertae objects (BLLs) constitute a class of active galactic nuclei (AGNs) with extreme observational features explained by non-thermal radiation from a relativistic jet nearly pointed along the observer’s line-of-sight. Their spectral energy distribution (SED), extending over 17-19 orders of the frequency, is of non-thermal origin and shows a typical two-humped structure. The lower-energy component, ranging from the radio to X-rays, is explained via synchrotron radiation emitted by ultra-relativistic electrons/positrons/protons, to be initially accelerated via the Blandford-Znajek mechanism or magneto-hydrodynamic processes in the vicinity of a central supermassive black hole. Afterwards, the particles should undergo further acceleration to ultra-relativistic energies by means of different mechanisms (first and second-order Fermi processes, relativistic magnetic reconnection, shear acceleration, jet-star interaction etc.) locally, in the jet emission zone. Our intensive X-ray spectral study of TeV-detected, high-energy-peaked BLLs (HBLs) often show the signatures of an effective second-order Fermi (stochastic) acceleration close to the shock front, while the processes related to the first-order Fermi acceleration are relatively rarely presented. The TeV-undetected HBLs and low-energy-peaked BLLs (LBLs) mostly do not show the signatures of efficient stochastic acceleration in their jets. Concerning the higher-energy component, the most frequently considered scenario incorporates an inverse Compton (IC) scattering of synchrotron photons by their ”parent” electron-positron population (synchrotron self-Compton model, SSC). However, this simple scenario sometimes is challenged by uncorrelated X-ray and TeV variability, more easily explained by multizone SSC, external Compton (EC) and hadronic scenarios.

Transient changes in muscle high-energy phosphates during moderate exercise

1993 ◽  
Vol 75 (2) ◽  
pp. 648-656 ◽  
Author(s):  
G. D. Marsh ◽  
D. H. Paterson ◽  
J. J. Potwarka ◽  
R. T. Thompson
Keyword(s):  
Oxygen Consumption ◽  
Steady State ◽  
Recovery Period ◽  
High Energy ◽  
Second Order ◽  
Moderate Intensity ◽  
High Energy Phosphates ◽  
Order Model ◽  
Time Constants ◽  
First Order

The purpose of this study was to use 31P-nuclear magnetic resonance spectroscopy to examine changes in wrist flexor muscle metabolism during the transitions from rest to steady-state exercise (on-transient) and back to rest (off-transient). Five healthy young males (mean age 25 +/- 2 yr) performed a series of square-wave exercise tests, each consisting of 5 min of moderate-intensity work followed by a 5-min recovery period. The subjects repeated this protocol six times, and each individual's results were pooled before analysis. ATP and intracellular pH did not change significantly during exercise or recovery. Phosphocreatine (PCr) declined progressively at the onset of exercise, reaching a plateau after approximately 2 min. A reciprocal increase in Pi occurred during the onset of exercise. During the recovery period PCr was resynthesized, whereas Pi returned to resting levels. The data were plotted as a function of time and fit with both first- and second-order exponential growth or decay models; however, the second-order model did not significantly improve the fit of the data. Time constants for the first-order model of the on- and off-transient responses for both PCr and Pi were approximately 30 s. These values are nearly identical to the time constants for oxygen consumption during submaximal exercise that have been reported previously by several authors. The results of this study show that the metabolism of muscle PCr during steady-state exercise and recovery can be accurately described by a monoexponential model and, further, suggest that a first-order proportionality exists between metabolic substrate utilization and oxygen consumption.

The swift observations of distant high-energy peaked BL Lacertae objects

2020 ◽  
Vol 365 (4) ◽  
Author(s):  
S. Kapanadze ◽  
B. Kapanadze ◽  
S. Vercellone ◽  
P. Romano ◽  
L. Neparidze
Keyword(s):  
High Energy ◽  
Bl Lacertae Objects ◽  
Bl Lacertae

Comparison of X-Ray– and Radio-selected BL Lacertae Objects in High-Energy Gamma-Ray Observations

1997 ◽  
Vol 476 (1) ◽  
pp. L11-L14 ◽  
Author(s):  
Y. C. Lin ◽  
D. L. Bertsch ◽  
B. L. Dingus ◽  
J. A. Esposito ◽  
C. E. Fichtel ◽  
...  
Keyword(s):  
Gamma Ray ◽  
High Energy ◽  
Bl Lacertae Objects ◽  
X Ray ◽  
Bl Lacertae ◽  
High Energy Gamma ◽  
Energy Gamma

scholarly journals Second order reflection from crystals used in soft X-ray spectroscopy

Nukleonika ◽  
2015 ◽  
Vol 60 (2) ◽  
pp. 263-265
Author(s):  
Ireneusz Książek
Keyword(s):  
Proportional Counter ◽  
Low Voltage ◽  
Pulse Height ◽  
Line Emission ◽  
Second Order ◽  
X Rays ◽  
X Ray ◽  
First Order ◽  
Order Reflection

Abstract In this note the ratio of the second to the first order reflection is determined for the KAP and PbSt crystals, for wavelengths corresponding to the Al K-line emission. The source of the radiation was a low-voltage stabilized X-ray tube. The X-rays were detected with a Bragg spectrometer equipped with a proportional counter detector. The signal measured by the proportional counter was subsequently pulse height analyzed.

X-rays and relativistic beaming in radio-selected BL Lacertae objects

1994 ◽  
Author(s):  
R. I. Kollgaard ◽  
E. D. Feigelson ◽  
D. C. Gabuzda ◽  
R. M. Sambruna ◽  
C. M. Urry
Keyword(s):  
X Rays ◽  
Bl Lacertae Objects ◽  
Bl Lacertae ◽  
Relativistic Beaming

scholarly journals A fast, very-high-energy γ-ray flare from BL Lacertae during a period of multi-wavelength activity in June 2015

2019 ◽  
Vol 623 ◽  
pp. A175 ◽  
Author(s):  
◽  
V. A. Acciari ◽  
S. Ansoldi ◽  
L. A. Antonelli ◽  
A. Arbet Engels ◽  
...  
Keyword(s):  
Spectral Energy Distribution ◽  
Interaction Model ◽  
High Energy ◽  
Spectral Energy ◽  
Polarization Angle ◽  
X Rays ◽  
Bl Lacertae ◽  
Multi Wavelength ◽  
Very High Energy ◽  
Very High

The mechanisms producing fast variability of the γ-ray emission in active galactic nuclei (AGNs) are under debate. The MAGIC telescopes detected a fast, very-high-energy (VHE, E  >  100 GeV) γ-ray flare from BL Lacertae on 2015 June 15. The flare had a maximum flux of (1.5 ± 0.3) × 10−10 photons cm−2 s−1 and halving time of 26 ± 8 min. The MAGIC observations were triggered by a high state in the optical and high-energy (HE, E  >  100 MeV) γ-ray bands. In this paper we present the MAGIC VHE γ-ray data together with multi-wavelength data from radio, optical, X-rays, and HE γ rays from 2015 May 1 to July 31. Well-sampled multi-wavelength data allow us to study the variability in detail and compare it to the other epochs when fast, VHE γ-ray flares have been detected from this source. Interestingly, we find that the behaviour in radio, optical, X-rays, and HE γ-rays is very similar to two other observed VHE γ-ray flares. In particular, also during this flare there was an indication of rotation of the optical polarization angle and of activity at the 43 GHz core. These repeating patterns indicate a connection between the three events. We also test modelling of the spectral energy distribution based on constraints from the light curves and VLBA observations, with two different geometrical setups of two-zone inverse Compton models. In addition we model the γ-ray data with the star-jet interaction model. We find that all of the tested emission models are compatible with the fast VHE γ-ray flare, but all have some tension with the multi-wavelength observations.

scholarly journals Radio to X-ray Energy Distribution of BL Lacertae Objects

1994 ◽  
Vol 159 ◽  
pp. 506-507
Author(s):  
P. Giommi ◽  
S. G. Ansari ◽  
A. Micol
Keyword(s):  
Energy Distribution ◽  
High Energy ◽  
Optical Spectra ◽  
Archival Data ◽  
Parent Population ◽  
Energy Distributions ◽  
Bl Lacertae Objects ◽  
X Ray ◽  
Bl Lacertae

We have constructed radio to X-ray energy distributions for a large number of BL Lacertae objects using archival data. We find that Radio to optical spectra of RBLs and XBLs are very similar. Large differences are seen at higher frequencies where RBLs very frequently show a cutoff near the optical band while XBLs usually do not show any turnover before UV/X-ray energies. Our data is consistent with a picture where RBL and XBL are from the same parent population, the XBL simply being those (rare) objects where the break in the energy distribution is located at high energy.

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