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— Illustration of the jet base of M87 down to the EHT-region scale. The right panel shows the actual image of M87 with VLBA at 43 GHz adopted from Hada et al. (2013). The yellow-green circle shows the one-zone region with its diameter 110 μ as which is investigated in K14. The EHT-region detected by Doeleman et al. (2012) is shown as the blue circle. Since Hada et al. (2011) indicate that the central engine of M87 is located at ∼ 41 μ as eastward of the radio core at 43 GHz, we put the the EHT-region around there. The left panel shows the illustration of internal structure inside the EHT-region. The red-colored region represents an SSA-thick compact region inside the SSA-thin region. The black-colored region conceptually shows a possible BH shadow image. According to the smallness of closure phase reported in Akiyama et al. (2015), a certain level of symmetry is kept in this picture.
Source publication
We explore the degree of magnetization at the jet base of M87 by using the
observational data of the event horizon telescope (EHT) at 230~GHz obtained by
Doeleman et al. By utilizing the method in Kino et al., we derive the energy
densities of magnetic fields ($U_{B}$) and electrons and positrons ($U_{\pm}$)
in the compact region detected by EHT (E...
Contexts in source publication
Context 1
... show an illustration of our scenario in Figure 1. In this solution, most of the correlated flux density detected by EHT is attributed to the emission from the SSA-thin region. ...
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Citations
... Leptonic jet models, in which energetic electrons radiate the multi-wavelength photons via synchrotron and inverse Compton scattering, are considered as the standard scenario (e.g., Abdo et al. 2009;MAGIC Collaboration et al. 2020). However, at least for M87, if we try to reproduce the observational data by the leptonic jet model, the magnetic field strength required to explain the multi-wavelength data is lower than that estimated by the observed core-shift in radio band (Kino et al. 2015;Jiang et al. 2021). If we use the core-shift-based magnetic field, the calculated gamma-ray flux is far below the observed gamma-ray flux (e.g., Lucchini et al. 2019;EHT MWL Science Working Group et al. 2021). ...
Radio galaxies are a subclass of active galactic nuclei that drive relativistic jets from their center and are observed in radio to very-high-energy gamma rays. The emission mechanisms and regions are still unknown. High-energy gamma rays can be explained by the emission from the magnetically arrested disks (MADs) around the central supermassive black hole, for which the magnetic flux threading the black hole is in a saturation level, although the emission from the MADs does not explain the optical and X-ray data. We construct a multi-wavelength emission model in which the optical and X-ray emission is emitted by jets and the gamma rays by MADs. Our model takes into account the particle injection by the magnetic reconnection at the jet base close to the black hole and particle entrainment from the ambient gas at the jet emission zone. We apply our model to M87 and find that our model can explain the simultaneous multi-wavelength data. In our model, the emission from the jets is the synchrotron radiation of the nonthermal electrons accelerated by magnetic reconnection, and the emission from the MADs is the synchrotron radiation mainly of the nonthermal protons accelerated by turbulence. We also find that the strong plasma entrainment is necessary to explain the multi-wavelength data. Our model will be tested by variability analysis among the multi-wavelength data.
... Walker et al. [10] explained the long-term sideways shifts observed in pc-scale jets as the propagation of a helical pattern created by KHI along the jet. However, it is unclear whether the newly discovered fast oscillation can be described by KHI, as the region observed by KaVA may be highly magnetized, e.g., [33]. Rather, currentdriven instability (CDI) such as sausage instability (m = 0) or kink instability (m = 1) can cause oscillations in the magnetically dominated regions e.g., [34][35][36]. ...
Recent VLBI monitoring has found transverse motions of the M87 jet. However, due to the limited cadence of previous observations, details of the transverse motion have not been fully revealed yet. We have regularly monitored the M87 jet at KVN and VERA Array (KaVA) 22 GHz from December 2013 to June 2016. The average time interval of the observation is ~ 0.1 year, which is suitable for tracking short-term structural changes. From these observations, the M87 jet is well represented by double ridge lines in the region 2 - 12 mas from the core. We found that the ridge lines exhibit transverse oscillations in all observed regions with an average period of $0.94\pm0.12$ years. When the sinusoidal fit is performed, we found that the amplitude of this oscillation is an order of $\sim0.1$ mas, and the oscillations in the northern and southern limbs are almost in phase. Considering the amplitude, it does not originate from Earth's parallax. We propose possible scenarios of the transverse oscillation, such as the propagation of jet instabilities or magneto-hydrodynamic (MHD) waves or perturbed mass injection around magnetically dominated accretion flows.
... Walker et al. [10] explained the long-term sideways shifts observed in pc-scale jets as the propagation of a helical pattern created by KHI along the jet. However, it is unclear whether the newly discovered fast oscillation can be described by KHI, as the region observed by KaVA may be highly magnetized, e.g., [33]. Rather, current-driven instability (CDI) such as sausage instability (m = 0) or kink instability (m = 1) can cause oscillations in the magnetically dominated regions e.g., [34][35][36]. ...
Recent VLBI monitoring has found transverse motions of the M87 jet. However, due to the limited cadence of previous observations, details of the transverse motion have not been fully revealed yet. We have regularly monitored the M87 jet at KVN and VERA Array (KaVA) 22 GHz from December 2013 to June 2016. The average time interval of the observation is ∼0.1 year, which is suitable for tracking short-term structural changes. From these observations, the M87 jet is well represented by double ridge lines in the region 2–12 mas from the core. We found that the ridge lines exhibit transverse oscillations in all observed regions with an average period of 0.94±0.12 years. When the sinusoidal fit is performed, we found that the amplitude of this oscillation is an order of ∼0.1 mas, and the oscillations in the northern and southern limbs are almost in phase. Considering the amplitude, it does not originate from Earth’s parallax. We propose possible scenarios of the transverse oscillation, such as the propagation of jet instabilities or magneto-hydrodynamic (MHD) waves or perturbed mass injection around magnetically dominated accretion flows.
... Consequently, M87 has been subject to wide studies at multi-frequencies from the radio to γ-rays [12], as well as the X-rays [13]. Furthermore, an extended study has also been conducted on its jet collimation using the Very Long Baseline Interferometry (VLBI) at sub-millimeter wavelengths [14][15][16][17][18][19][20][21][22]. The synchrotron spectrum of M87 jet was first studied in [23]. ...
We explore the plasma matter content in the innermost accretion disk/jet in M87* as relevant for an enthusiastic search for the signatures of anti-matter in the next generation of the Event Horizon Telescope (ngEHT). We model the impact of non-zero positron-to-electron ratio using different emission models, including a constant electron to magnetic pressure (constant βe model) with a population of non-thermal electrons as well as an R-beta model populated with thermal electrons. In the former case, we pick a semi-analytic fit to the force-free region of a general relativistic magnetohydrodynamic (GRMHD) simulation, while in the latter case, we analyze the GRMHD simulations directly. In both cases, positrons are being added at the post-processing level. We generate polarized images and spectra for some of these models and find out that at the radio frequencies, both of the linear and the circular polarizations are enhanced with every pair added. On the contrary, we show that, at higher frequencies, a substantial positron fraction washes out the circular polarization. We report strong degeneracies between different emission models and the positron fraction, though our non-thermal models show more sensitivities to the pair fraction than the thermal models. We conclude that a large theoretical image library is indeed required to fully understand the trends probed in this study, and to place them in the context of a large set of parameters which also affect polarimetric images, such as magnetic field strength, black hole spin, and detailed aspects of the electron temperature and the distribution function.
... Consequently, M87 has been subject to wide studies at multi-frequencies from the radio to γ-rays [10], as well as the X-rays [11]. Furthermore, there have been also an extended study on its jet collimation using the Very Long Baseline Interferometry (VLBI) at sub-millimeter wavelengths [12][13][14][15][16][17][18][19][20]. The synchrotron spectrum of M87 jet was first studied in [21]. ...
We explore the plasma matter content in the innermost accretion disk/jet in M87* as relevant for an enthusiastic search for the signatures of anti-matter in the next generation of the Event Horizon Telescope (ngEHT). We model the impact of non-zero positron-to-electron ratio using different emission models including a constant electron to magnetic pressure (constant $\beta_e$ model) with a population of non-thermal electrons as well as a R-beta model populated with thermal electrons. In the former case, we pick a semi-analytic fit to the force-free region of a general relativistic magnetohydrodynamic (GRMHD) simulation, while in the latter case, we analyze the GRMHD simulations directly. In both cases, positrons are being added at the post-processing level. We generate polarized images and spectra for some of these models and find out that at the radio frequencies, both of the linear and the circular polarizations get enhanced per adding pairs. On the contrary, we show that at higher frequencies a substantial positron fraction washes out the circular polarization. We report strong degeneracies between different emission models and the positron fraction, though our non-thermal models show more sensitivities to the pair fraction than the thermal models. We conclude that a large theoretical image library is indeed required to fully understand the trends probed in this study, and to place them in the context of large set of parameters which also affect polarimetric images, such as magnetic field strength, black hole spin, and detailed aspects of the electron temperature and the distribution function.
... Based on millimeter/submillimeter VLBI observations, the jet base of M87 has been indicated to be magnetic-energydominated based on the energetics at the optically thick region against the synchrotron self-absorption (SSA) process (Kino et al. , 2015b. Now it is widely considered that the magnetic field plays an important role in the formation of the relativistic jet (e.g., Blandford et al. 2019). ...
... 14 In general, there is a limitation for constraining a magnetization degree at a jet base from the spectral energy distribution (SED) fitting of multiwavelength (MWL) data as collected flux data do not share a common single emission region due to the different angular resolutions of various telescopes. To overcome the limitation of MWL SED fitting, Kino et al. (2014) and Kino et al. (2015b) explore the energetics at the M87 jet base based on VLBI data together with the well-established process of synchrotron self-absorption (SSA). In Figure 8 . ...
... In Figure 8 . Unfortunately, the submillimeter radio-emitting 40 μas region (Kino et al. , 2015b; EHT MWL Science Working Group et al. 2021) is within the light cylinder, which is not described by TT03. Therefore, it is not possible to directly compare the obtained σ profile with the constrained σ in those previous works. ...
Motivated by the measured velocity profile of the M87 jet using the Korean very-long-baseline interferometry (VLBI) network (KVN) and VLBI Exploration of Radio Astrometry (VERA) Array (KaVA) by Park et al. indicating that the starting position of the jet acceleration is farther from the central engine of the jet than predicted in general relativistic magnetohydrodynamic simulations, we explore how to mitigate the apparent discrepancy between the simulations and the KaVA observation. We use a semi-analytic jet model proposed by Tomimatsu & Takahashi consistently solving the transmagnetic field structure but neglecting any dissipation effects. By comparing the jet model with the observed M87 jet velocity profile, we find that the model can reproduce the logarithmic feature of the velocity profile and can fit the observed data when choosing c /(100 r g ) ≲ Ω F ≲ c /(70 r g ), where r g is the gravitational radius. While a total specific energy ( ) of the jet changes the terminal bulk Lorentz factor of the jet, a slower angular velocity of the black hole magnetosphere (Ω F ) makes a light-cylinder radius ( r lc ) larger, and it consequently pushes out a location of a starting point of the jet acceleration. Using the estimated Ω F we further estimate the magnetic field strength on the event horizon scale in M87 by assuming Blandford–Znajek process is in action. The corresponding magnetic flux threading the event horizon of M87 is in good agreement with a magnetically arrested disk regime.
... These mechanisms can efficiently create e + e − pairs when the accretion rate is high. However, the estimated multiplicity is ∼ 100-10 3 , which is still lower than the required multiplicity estimated by radio observations (κ ± 10 5 ; see, e.g., Kino et al. 2015). ...
Supermassive black holes in active galactic nuclei launch relativistic jets, as indicated by observed superluminal radio blobs. The energy source of these jets is widely discussed in the theoretical framework of the Blandford–Znajek process, the electromagnetic energy extraction from rotating black holes (BHs), while the formation mechanism of the radio blobs in the electromagnetically dominated jets has been a long-standing problem. Recent high-resolution magnetohydrodynamic simulations of magnetically arrested disks exhibited magnetic reconnection in a transient magnetically dominated part of the equatorial disk near the BH horizon, which led to a promising scenario of efficient MeV gamma-ray production and subsequent electron–positron pair loading into the BH magnetosphere. We develop this scenario to build a theoretical framework on energetics, timescales, and particle number density of the superluminal radio blobs and discuss observable signatures in other wave bands. We analytically show that the nonthermal electrons emit broadband photons from optical to multi-MeV bands. The electron–positron pairs produced in the magnetosphere are optically thick for synchrotron self-absorption, so that the injected energy is stored in the plasma. The stored energy is enough to power the superluminal radio blobs observed in M87. This scenario predicts rather dim radio blobs around Sgr A*, which are consistent with no clear detection by current facilities. In addition, this scenario inevitably produces strong X-ray flares in a short timescale, which will be detectable by future X-ray satellites.
... Based on mm/sub-mm VLBI observations, the jet base of M87 has been indicated to be magnetic-energy dominated based on the energetics at the optically thick region against synchrotron self-absorption (SSA) process (Kino et al. , 2015b. Now it is widely considered that magnetic field plays an important role in the formation of the relativistic jet (e.g., Blandford et al. 2019). ...
... 4 In general, there is a limitation for constraining a magnetization degree at a jet base from spectral energy distribution (SED) fitting of multi-wavelengths (MWL) data since collected flux data do not share a common single emission region due to different angular resolution of various telescopes. To overcome the limitation of MWL SED fitting, Kino et al. (2014) and Kino et al. (2015b) explore the energetics at the M87 jet base based on VLBI data alone together with the well-established process of synchrotron self-absorption (SSA). In Figure 7, we include these values in the literatures by setting σ = E EM /E MA ≈ U B /U ± . ...
... In Figure 7, we include these values in the literatures by setting σ = E EM /E MA ≈ U B /U ± . Unfortunately, sub-mm radio-emitting 40 µas region in (Kino et al. , 2015bEHT MWL Science Working Group et al. 2021) is within the light cylinder, which is not described by TT03. Therefore, it is not possible to directly compare the obtained σ profile with the constrained σ those previous works. ...
Motivated by the measured velocity profile of the M87 jet using the KVN and VERA Array (KaVA) by Park et al. indicating that the starting position of the jet acceleration is farther from the central engine of the jet than predicted in general relativistic magnetohydrodynamic simulations, we explore how to mitigate the apparent discrepancy between the simulations and the KaVA observation. We use a semi-analytic jet model proposed by Tomimatsu and Takahashi. consistently solving the trans-magnetic field structure but neglecting any dissipation effects. By comparing the jet model with the observed M87 jet velocity profile, we find that the model can reproduce the logarithmic feature of the velocity profile, and can fit the observed data when choosing $c/(100r_{g}) \lesssim \Omega_{F} \lesssim c/(70r_{g})$ where $r_{g}$ is the gravitational radius. While a total specific energy (${\cal E}$) of the jet changes the terminal bulk Lorentz factor of the jet, a slower angular velocity of the black hole magnetosphere (funnel region) ($\Omega_{F}$) makes a light-cylinder radius ($r_{\rm lc}$) larger and it consequently pushes out a location of a starting point of the jet acceleration. Using the estimated $\Omega_{F}$ we further estimate the magnetic field strength on the event horizon scale in M87 by assuming Blandford-Znajek (BZ) process is in action. The corresponding magnetic flux threading the event horizon of M87 is in good agreement with a magnetically arrested disc (MAD) regime.
... These mechanisms can efficiently create e + e − pairs when accretion rate is high. However, the estimated multiplicity is ∼ 100 − 10 3 , which is still lower than the required multiplicity estimated by radio observations (κ ± 10 5 ; see e.g., Kino et al. 2015). ...
Supermassive black holes in active galactic nuclei launch relativistic jets, as indicated by observed superluminal radio blobs. The energy source of these jets is widely discussed in the theoretical framework of Blandford-Znajek process, the electromagnetic energy extraction from rotating black holes (BHs), while formation mechanism of the radio blobs in the electromagnetically-dominated jets has been a long-standing problem. Recent high-resolution magnetohydrodynamic simulations of magnetically arrested disks exhibited magnetic reconnection in a transient magnetically-dominated part of the equatorial disk near the BH horizon, which led to a promising scenario of efficient MeV gamma-ray production and subsequent electron-positron pair loading into BH magnetosphere. We develop this scenario to build a theoretical framework on energetics, timescales and particle number density of the superluminal radio blobs and discuss observable signatures in other wavebands. We analytically show that the non-thermal electrons emit broadband photons from optical to multi-MeV bands. The electron-positron pairs produced in the magnetosphere are optically thick for synchrotron-self absorption, so that the injected energy is stored in the plasma. The stored energy is enough to power the superluminal radio blobs observed in M87. This scenario predicts rather dim radio blobs around Sgr A*, which are consistent with no clear detection by current facilities. In addition, this scenario inevitably produces strong X-ray flares in a short timescale, which will be detectable by future X-ray satellites.
... The gamma-ray production sites for radio galaxies are controversial because relativistic beaming effects should be weaker in these objects. Leptonic compact jet models are actively discussed as a standard scenario (e.g., Abdo et al. 2009;MAGIC Collaboration et al. 2020), but, at least in M87, this scenario failed to reproduce the magnetic field strength estimated by core-shift measurements in the radio bands (Kino et al. 2015;Jiang et al. 2021). If we assume the strong magnetic fields given by the radio observations, the resulting gamma-ray spectra are far below the observed flux (Event Horizon Telescope MWL Science Working Group et al. 2021). ...
The origins of the GeV gamma rays from nearby radio galaxies are unknown. Hadronic emission from magnetically arrested disks (MADs) around central black holes is proposed as a possible scenario. Particles are accelerated in a MAD by magnetic reconnection and stochastic turbulence acceleration. We pick out the 15 brightest radio galaxies in the GeV band from The Fourth Catalog of Active Galactic Nuclei Detected by the Fermi Large Area Telescope, Data Release 2 and apply the MAD model. We find that we can explain the data in the GeV bands by the MAD model if the accretion rate is lower than 0.1% of the Eddington rate. For a higher accretion rate, GeV gamma rays are absorbed by two-photon interaction due to copious low-energy photons. If we assume another proposed prescription of the electron-heating rate by magnetic reconnection, the MAD model fails to reproduce the GeV data for the majority of our sample. This indicates that the electron-heating rate is crucial. We also apply the MAD model to Sagittarius A* (Sgr A*) and find that GeV gamma rays observed at the Galactic center do not come from the MAD of Sgr A*. We estimate the cosmic ray (CR) intensity from Sgr A*, but it is too low to explain the high-energy CR intensity on Earth.
