Abstract
Radiatively inefficient accretion flow models have been shown to accurately account for the spectrum and luminosity observed from Sgr A* in the X-ray regime down to mm wavelengths. However, ...observations at a few GHz cannot be explained by thermal electrons alone but require the presence of an additional non-thermal particle population. Here, we propose a model for the origin of such a population in the accretion flow via means of a pulsar orbiting the supermassive black hole in our Galaxy. Interactions between the relativistic pulsar wind with the disc lead to the formation of a bow shock in the wind. During the pulsar’s transit through the accretion disc, relativistic pairs, accelerated at the shock front, are injected into the disc. The radio-emitting particles are long lived and remain within the disc long after the pulsar’s transit. Periodic pulsar transits through the disc result in regular injection episodes of non-thermal particles. We show that for a pulsar with spin-down luminosity L
sd ∼ 3 × 1035 erg s−1 and a wind Lorentz factor of γw ∼ 104 a quasi-steady synchrotron emission is established with luminosities in the 1–10 GHz range comparable to the observed one.
Aims. We have studied a mechanism for producing intrinsic broken power-law γ-ray spectra in compact sources. This is based on the principles of automatic photon quenching, according to which γ-rays ...are being absorbed on spontaneously produced soft photons whenever the injected luminosity in γ-rays lies above a certain critical value. Methods. We derived an analytical expression for the critical γ-ray compactness in the case of power-law injection. For the case where automatic photon quenching is relevant, we calculated analytically the emergent steady-state γ-ray spectra. We also performed numerical calculations in order to back up our analytical results. Results. We show that a spontaneously quenched power-law γ-ray spectrum obtains a photon index 3Γ/2, where Γ is the photon index of the power-law at injection. Thus, large spectral breaks of the γ-ray photon spectrum, e.g. ΔΓ ≳ 1, can be obtained by this mechanism. We also discuss additional features of this mechanism that can be tested observationally. Finally, we fit the multiwavelength spectrum of a newly discovered blazar (PKS 0447-439) by using such parameters to explain the break in the γ-ray spectrum by means of spontaneous photon quenching, under the assumption that its redshift lies in the range 0.1 < z < 0.24.
The recent IceCube discovery of 0.1–1 PeV neutrinos of astrophysical origin opens up a new era for high-energy astrophysics. Although there are various astrophysical candidate sources, a firm ...association of the detected neutrinos with one (or more) of them is still lacking. A recent analysis of plausible astrophysical counterparts within the error circles of IceCube events showed that likely counterparts for nine of the IceCube neutrinos include mostly BL Lacs, among which Mrk 421. Motivated by this result and a previous independent analysis on the neutrino emission from Mrk 421, we test the BL Lac–neutrino connection in the context of a specific theoretical model for BL Lac emission. We model the spectral energy distribution (SED) of the BL Lacs selected as counterparts of the IceCube neutrinos using a one-zone leptohadronic model and mostly nearly simultaneous data. The neutrino flux for each BL Lac is self-consistently calculated, using photon and proton distributions specifically derived for every individual source. We find that the SEDs of the sample, although different in shape and flux, are all well fitted by the model using reasonable parameter values. Moreover, the model-predicted neutrino flux and energy for these sources are of the same order of magnitude as those of the IceCube neutrinos. In two cases, namely Mrk 421 and 1H 1914−194, we find a suggestively good agreement between the model prediction and the detected neutrino flux. Our predictions for all the BL Lacs of the sample are in the range to be confirmed or disputed by IceCube in the next few years of data sampling.
Context.
Black-hole X-ray binaries (BHXRBs) in the hard and hard-intermediate spectral (and temporal) states exhibit in their power spectra characteristic frequencies called type-C quasi-periodic ...oscillations (QPOs). Various models that can explain them with various degrees of success have been proposed, but a definitive answer is still missing.
Aims.
The hot Comptonizing corona interacting with the cold accretion disk, both of which are central in understanding BHXRBs, is essentially a dynamical system. Our aim is to investigate if the radiative coupling between the two components can produce QPOs.
Methods.
We write and solve the time-dependent equations that describe energy conservation in the system corona – accretion disk. We examine both constant and variable mass accretion rates. By necessity, in this first investigation we use a simple model, but it contains all the essential ingredients.
Results.
For a constant mass accretion rate and certain justifiable conditions, the dynamic corona – disk system exhibits oscillations, which die out after a few cycles. The characteristic frequencies of these oscillations are similar to the ones observed in the power spectra of BHXRBs. For most parameters, the natural frequencies persist even in the case of variable accretion rates.
Conclusions.
We argue that type-C QPOs in BHXRBs could, in principle, arise from the interaction of the hot Comptonizing corona with the much colder accretion disk. If this picture is correct, it has immediate implications for other systems that contain the above constituents, such as active galactic nuclei.
Aims. We investigate the behavior of the frequency-centered light curves expected within the standard model of gamma ray bursts, allowing the maximum electron energy (γmax) to be a free parameter ...that may take low values. Methods. We solve the spatially averaged kinetic equations that describe the simultaneous evolution of particles and photons, obtaining the multi-wavelength spectra as a function of time. From these we construct the frequency-centered light curves with an emphasis on the X-ray and optical bands. Results. We show that in cases where γmax takes low values, the produced X-ray light curves show a plateau as the synchrotron component gives its place to the synchrotron self-Compton one in the X-ray band.
•Correlations of Mn species from serum and cerebrospinal fluid based on an extended sample set of 180 samples.•Differentiated analysis of such correlations with respect to the three different regions ...of origin of the samples (from Munich, Germany, from the Emilia Romagna region in Italy, and from Sweden).•Proof of a change in Mn-carrier from Mn-transferrin to Mn-citrate, depending on the total Mn concentration in serum.•The reliability of ultrafiltration versus SEC under practical conditions for occupational health laboratories was elucidated aiming whether the same results are gained by both methods and under which conditions (i.e., simpler procedure of pre-cleaning of tubes, or concentration dependence of performance).•For both methods (SEC-ICP-DRC-MS, and: UF→ICP-DRC-MS) quality control data including precision of analytical performance and recovery are provided
After high-dose-short-term exposure (usually from occupational exposure) and even more under low-dose long term exposure (mainly environmental) manganese (Mn) biomonitoring is still problematic since these exposure scenarios are not necessarily reflected by a significant increase of total Mn in blood or serum. Usually, Mn concentrations of exposed and unexposed persons overlap and individual differentiation is often not possible. In this paper Mn speciation on a large sample size (n=180) was used in order to be able to differentiate between highly Mn-exposed or low or unexposed individuals at low total Mn concentration in serum (Mn(S)). The whole sample set consisted of three subsets from Munich, Emilia Romagna region in Italy and from Sweden. It turned out that also at low total Mn(S) concentrations a change in major Mn carriers in serum takes place from Mn-transferrin (Mn-Tf(S)) towards Mn-citrate (Mn-Cit(S)) with high statistical significance (p<0.000002). This carrier switch from Mn-Tf(S) to Mn-Cit(S) was observed between Mn(S) concentrations of 1.5μg/L to ca. 1.7μg/L. Parallel to this carrier change, for sample donors from Munich where serum and cerebrospinal fluid were available, the concentration of Mn beyond neural barriers – analysed as Mn in cerebrospinal fluid (Mn(C)) – positively correlates to Mn-Cit(S) when Mn(S) concentration was above 1.7μg/L. The correlation between Mn-Cit(S) and Mn(C) reflects the facilitated Mn transport through neural barrier by means of Mn-citrate. Regional differences in switch points from Mn-Tf(S) to Mn-Cit(S) were observed for the three sample subsets. It is currently unknown whether these differences are due to differences in location, occupation, health status or other aspects. Based on our results, Mn-Cit(S) determination was considered as a potential means for estimating the Mn load in brain and CSF, i.e., it could be used as a biomarker for Mn beyond neural barrier. For a simpler Mn-Cit(S) determination than size exclusion chromatography inductively coupled plasma mass spectrometry (SEC-ICP-MS), ultrafiltration (UF) of serum samples was tested for suitability, the latter possibly being a preferred choice for routine occupational medicine laboratories. Our results revealed that UF could be an alternative if methodical prerequisites and limitations are carefully considered. These prerequisites were determined to be a thorough cleaning procedure at a minimum Mn(S) concentration >1.5μg/L, as at lower concentrations a wide scattering of the measured concentrations in comparison to the standardized SEC-ICP-MS results were observed.
Context . Recent associations of high-energy neutrinos with active galactic nuclei (AGN) have revived the interest in leptohadronic models of radiation from astrophysical sources. The rapid increase ...in the amount of acquired multi-messenger data will require fast numerical models that may be applied to large source samples. Aims . We develop a time-dependent leptohadronic code, LeHaMoC , that offers several notable benefits compared to other existing codes, such as versatility and speed. Methods . LeHaMoC solves the Fokker-Planck equations of photons and relativistic particles (i.e. electrons, positrons, protons, and neutrinos) produced in a homogeneous magnetized source that may also be expanding. The code utilizes a fully implicit difference scheme that allows fast computation of steady-state and dynamically evolving physical problems. Results . We first present test cases where we compare the numerical results obtained with LeHaMoC against exact analytical solutions and numerical results computed with ATHE v A, a well-tested code of similar philosophy but a different numerical implementation. We find a good agreement (within 10–30%) with the numerical results obtained with ATHE v A without evidence of systematic differences. We then demonstrate the capabilities of the code through illustrative examples. First, we fit the spectral energy distribution from a jetted AGN in the context of a synchrotron-self Compton model and a proton-synchrotron model using Bayesian inference. Second, we compute the high-energy neutrino signal and the electromagnetic cascade induced by hadronic interactions in the corona of NGC 1068. Conclusions . LeHaMoC is easily customized to model a variety of high-energy astrophysical sources and has the potential to become a widely utilized tool in multi-messenger astrophysics.
A hadronic minute-scale GeV flare from quasar 3C 279? Petropoulou, M.; Nalewajko, K.; Hayashida, M. ...
Monthly notices of the Royal Astronomical Society. Letters,
05/2017, Letnik:
467, Številka:
1
Journal Article
Recenzirano
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Abstract The flat spectrum radio quasar 3C 279 is a known γ-ray variable source that has recently exhibited minute-scale variability at energies >100 MeV. One-zone leptonic models for blazar emission ...are severely constrained by the short time-scale variability that implies a very compact emission region at a distance of hundreds of Schwarzschild radii from the central black hole. Here, we investigate a hadronic scenario where GeV γ-rays are produced via proton synchrotron radiation. We also take into account the effects of the hadronically initiated electromagnetic cascades (EMC). For a γ-ray emitting region in rough equipartition between particles and kG magnetic fields, located within the broad-line region (BLR), the development of EMC redistributes the γ-ray luminosity to softer energy bands and eventually leads to broad-band spectra that differ from the observed ones. Suppression of EMC and energy equipartition are still possible, if the γ-ray emitting region is located beyond the BLR, is fast moving with Doppler factor (>70) and contains strong magnetic fields (>100 G). Yet, these conditions cannot be easily met in parsec-scale jets, thus disfavouring a proton synchrotron origin of the Fermi-LAT flare.
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