122184067
A Jet Deceleration Model on TeV BL Lacertae Objects
The current understanding of the kinetics of known TeV BL Lac objects' jets is that they substantially decelerate from a subparsec scale with a large Lorentz factor, emitting TeV radiation to a parsec scale, where the observed radio component is predominantly subluminal or mildly relativistic. A decelerating jet model of TeV BL Lac objects including jet dynamics and particle injection is proposed. The jet plasma is assumed to be continuously injected at the base of the jet and to dissipate at some distance from the central core. It is found that the deceleration profile of the jet depends on the density distribution of the external medium, showing slower variation in an external medium with a fast-falling density profile. The dissipated kinetic energy of the jet is assumed to be transferred to electron acceleration. The relativistic electrons are injected along the jet and then produce synchrotron and inverse Compton emission. The general characteristics of the physical quantities of the jet are discussed. It is shown that the resulting spectral energy distributions (SEDs) mainly depend on the energy distribution of injected electrons in the dissipation region, the magnetic structure, and the viewing angle of the jet. The model describes the underlying undisturbed jet and is applied to fit the quiescent infrared to X-ray spectra of several TeV BL Lac objects. In this scenario, the dissipated bulk kinetic energy of TeV BL Lac objects can provide relativistic electrons for radiation, and their initial magnetic fields are under equipartition with the emitting electrons.
14071619
The Mass Distribution of Black Holes in BL Lacertae Objects
In this {\it Letter}, we make an attempt to estimate the masses of black holes and their distributions in BL Lac objects. We find there is a bimodal population of black hole masses in BL Lacs: the first has a lower-mass peak centred at $\sim 7.0 \times 10^6\sunm$ composed of high frequency-peaked BL Lacs (HBLs) and the second is a higher-mass ($>10^9\sunm$) population composed of low frequency-peaked BL Lacs (LBLs). The low mass family of black holes in HBLs does not satisfy the Magorrian et al. relation whereas the high mass family in LBLs does this relation and is in agreement with Laor's limit. The origination of the bimodal distribution of black hole mass remains open.
17321754
Implications of Bulk Velocity Structures in AGN Jets
Synchrotron self-Compton (SSC) models and External Compton (EC) models of AGN jets with continually longitudinal and transverse bulk velocity structures have been constructed. The observed spectra show complex and interesting patterns in different velocity structures and viewing angles. These models were used to calculate the synchrotron and inverse Compton spectra of two typical BL Lac objects (BLO) (Mrk 421 and 0716+714) and (one) Flat Spectrum Radio Quasars (FSRQs) (3C 279), and to discuss the implications of jet bulk velocity structures in a unification of the BLO and FR I radio galaxies (FRI). By calculating the synchrotron spectra and SSC spectra of BL Lac object jets with continually bulk velocity structures, we have found that the spectra are much different from those in jets with a uniform velocity structure under increasing viewing angles. The unification of BLO and FRI is less constrained by the viewing angles, and would be imprinted by velocity structures intrinsic to the jets, themselves. By considering jets with bulk velocity structures constrained by the apparent speed, we discuss the velocity structures imprinted on the observed spectra for different viewing angles. We find that the spectra are greatly impacted by longitudinal velocity structures, because the volume elements are compressed or expanded. Finally, we present the EC spectra of FSRQs and FR II radio galaxies (FRII), and find that they are weakly affected by the velocity structures compared to synchrotron and SSC spectra.
118677286
Gamma-ray Burst Prompt Emission: Jitter Radiation in Stochastic Magnetic Field Revisited
We revisit the radiation mechanism of relativistic electrons in the stochastic magnetic field and apply it to the high-energy emissions of gamma-ray bursts (GRBs). We confirm that jitter radiation is a possible explanation for GRB prompt emission in the condition of a large electron deflection angle. In the turbulent scenario, the radiative spectral property of GRB prompt emission is decided by the kinetic energy spectrum of turbulence. The intensity of the random and small-scale magnetic field is determined by the viscous scale of the turbulent eddy. The microphysical parameters epsilon(e) and epsilon(B) can be obtained. The acceleration and cooling timescales are estimated as well. Due to particle acceleration in magnetized filamentary turbulence, the maximum energy released from the relativistic electrons can reach a value of about 10(14) eV. The GeV GRBs are possible sources of high-energy cosmic-ray.
17685255
Knot in centaurus A: A stochastic magnetic field for diffusive synchrotron radiation?
The emission of relativistic electrons moving in the random and small-scale magnetic field is presented by diffusive synchrotron radiation (DSR). In this Letter, we revisit the perturbative treatment of DSR. We propose that a random and small-scale magnetic field might be generated by the turbulence. As an example, multiband radiation of the knot in Cen A comes from the electrons with energy gamma(e) similar to 10(3 -) 10(4) in the magnetic field of 10(-3) G. The multiband spectrum of DSR is well determined by the feature of a stochastic magnetic field. These results put strong constraints on the models of particle acceleration.
118436895
Mechanism of very high energy radiation in BL Lacertae object 3C 66A
Aims. Our goal is to understand the nature of blazars and the mechanisms for generating high-energy.-rays, through investigation of the blazar 3C 66A. Methods. We model the high-energy spectrum of 3C 66A, which was observed recently with the Fermi-LAT and VERITAS telescopes. The spectrum has a hard change from the energy range of 0.2-100 GeV to 200-500 GeV in recent almost contemporaneous observations of two telescopes. Results. The de-absorbed VERITAS spectrum depends strongly on redshift, which is highly uncertain. If z = 0.444 is adopted, we are able to use the SSC model to produce the Fermi-LAT component and the EC model to the VERITAS component. However, if z = 0.1, the intrinsic VERITAS spectrum will be softer, and there will be a smooth link between the Fermi-LAT and VERITAS spectra that can be explained using an SSC model.
118979006
Collisions among Clouds inside Dusty Tori in Active Galactic Nuclei: Observational Consequences
A geometrically thick dusty torus in NGC 1068 has been unambiguously resolved by an infrared interferometry telescope. This implies that clouds composing the dusty torus are undergoing supersonic collisions with each other. We show that the collisions form strong nonrelativistic shocks, which accelerate populations of relativistic electrons. The torus reprocesses emission from the accretion disk into an infrared band. We show that the energy density of the infrared photons inside the torus is much higher than that of the magnetic field in the clouds, and the seed photons of inverse Compton scattering are mainly from the infrared. The maximum energy of the relativistic electrons can reach a Lorentz factor of 105. We calculate the spectrum of the synchrotron and inverse Compton scattering radiation from the electrons in the torus. The relativistic electrons in the torus radiate nonthermal emission from radio to γ-ray, which isotropically diffuses in the region of the torus. We find that the most prominent character is a peak at ~0.5-1 GeV. We apply this model to NGC 1068 and find that the observed radio emission from the core component S1 can be explained by the synchrotron emission from the relativistic electrons. We predict that there is γ-ray emission with a luminosity of 1040 ergs s-1 peaking at ~1 GeV from the torus, which could be detected by the Gamma-Ray Large-Array Space Telescope in the future. This will provide a new clue to understanding the physics in the torus. The nonthermal radiation from the dusty torus may explain the radio emission from Seyfert galaxies. The cosmological implications of the nonthermal emission to the γ-ray background radiation are also discussed.
122834865
Performance of CMS hadron calorimeter timing and synchronization using test beam, cosmic ray, and LHC beam data
This paper discusses the design and performance of the time measurement technique and of the synchronization systems of the CMS hadron calorimeter. Time measurement performance results are presented from test beam data taken in the years 2004 and 2006. For hadronic showers of energy greater than 100 GeV, the timing resolution is measured to be about 1.2 ns. Time synchronization and out-of-time background rejection results are presented from the Cosmic Run At Four Tesla and LHC beam runs taken in the Autumn of 2008. The inter-channel synchronization is measured to be within ±2 ns.
119176140
A general relativistic external Compton-scattering model for TeV emission from M87
M87 is the first detected non-blazar extragalactic Tera-Ele ctron-Volt (TeV) source with rapid variation and very flat spectrum in the TeV band. To explain the two-peaks in the spectral energy distribution (SED) of the nucleus of M87 which is similar to those of blazars, the most commonly adopted models are the synchrotron self-Compton scattering (SSC) models and the external inverse Compton scattering (EIC) models. Considering that there is no correlated variation in the soft band (from r adio to X-ray) matching the TeV variation, and the TeV sources should not suffer from the γγ absorption due to the flat TeV spectrum, the EIC models are advantageous in modeling the TeV emission from M87. In this paper, we propose a self-consistent EIC model to explain the flat TeV spectrum of M87 within the framework of fully general relativity, where the background soft photons are from the advection-dominated accretion flo w (ADAF) around the central black hole, and the high energy electrons are from the mini-jets which are powered by the magnetic reconnection in the main jet (Giannios et al. 2010). In our model, both the TeV flares obser ved in the years of 2005 and 2008 could be well explained: the γγ absorption for TeV photons is very low, even inside the region very close to the black hole 20Rg ∼ 50Rg; at the same region, the average EIC cooling time (∼ 10 2 ∼ 10 3 s) is short, which is consistent with the observed time scale of TeV variation. Furthermore, we also discuss the possibility that the accompanying X-ray flare in 2008 is due to the direct synchrotron radiation of the mini-jets. Subject headings:black hole physics — galaxies: individual (M87)
119360994
The 172 ks Chandra Exposure of the LALA Bootes Field: X-Ray Source Catalog
We present an analysis of a deep, 172 ks Chandra observation of the Large Area Lyman Alpha survey (LALA) Bootes field, obtained with the Advanced CCD Imaging Spectrometer (ACIS-I) on board the Chandra X-Ray Observatory. This is one of the deepest Chandra images of the extragalactic sky; only the 2 Ms Chandra Deep Field North (CDF-N) and 1 Ms Chandra Deep Field South (CDF-S) are substantially deeper. In this paper we present the X-ray source catalog obtained from this image, along with an analysis of source counts and optical identifications. The X-ray image is composed of two individual observations obtained in 2002 and reaches 0.5–2.0 and 2.0–10.0 keV flux limits of 1.5 × 10-16 and 1.0 × 10-15 ergs cm-2 s-1, respectively, for point sources near the aim point. A total of 168 X-ray sources were detected: 160 in the 0.5–7.0 keV band, 132 in the 0.5–2.0 keV band, and 111 in the 2.0–7.0 keV band. The X-ray source counts were derived and compared with those from other Chandra deep surveys; the hard X-ray source density of the LALA Bootes field is 33% higher than that of CDF-S at the flux level of 2.0 × 10-15 ergs cm-2 s-1, confirming the field-to-field variances of the hard-band source counts reported by previous studies. The deep exposure resolves 72% of the 2.0–10.0 keV X-ray background. Our primary optical data are R-band imaging from the NOAO Deep Wide-Field Survey (NDWFS), with a limiting magnitude of R = 25.7 (Vega, 3 σ, and 4'' diameter aperture). We have found optical counterparts for 152 of the 168 Chandra sources (90%); 144 of these are detected in the R-band image, and eight have optical counterparts in other bands (either BW, V, I, or z'). Among the R-band nondetected sources, not more than 11 of them can possibly be at z > 5, based on the hardness ratios of their X-ray emission and nondetections in bluer bands (BW, V). The majority (~76%) of the X-ray sources are found to have log(fX/fR) within 0.0 ± 1; these are believed to be AGNs. Most of the X-ray–faint/optically bright sources [log(fX/fR) 1.0], which are harder in X-ray and are probably obscured AGNs.
209834953
Commissioning of the CMS High-Level Trigger with Cosmic Rays
The CMS High-Level Trigger (HLT) is responsible for ensuring that data samples with potentially interesting events are recorded with high efficiency and good quality. This paper gives an overview of the HLT and focuses on its commissioning using cosmic rays. The selection of triggers that were deployed is presented and the online grouping of triggered events into streams and primary datasets is discussed. Tools for online and offline data quality monitoring for the HLT are described, and the operational performance of the muon HLT algorithms is reviewed. The average time taken for the HLT selection and its dependence on detector and operating conditions are presented. The HLT performed reliably and helped provide a large dataset. This dataset has proven to be invaluable for understanding the performance of the trigger and the CMS experiment as a whole.