Research

Title: The centimeter-to-submillimeter broad-band radio spectrum of the central compact component in a nearby type-II Seyfert galaxy NGC 1068.
Authors: Tomonari Michiyama, Yoshiyuki Inoue, Akihiro Doi

We analyze all the available Atacama Large Millimeter / submillimeter Array archival data of the nearby Type-II Seyfert galaxy NGC 1068, including new 100 GHz data with the angular resolution of 0\farcs05, which was not included in previous continuum spectral analysis. By combining with the literature data based on the Very Large Array, we investigate the broadband radio continuum spectrum of the central ≲7 pc region of NGC 1068. We found that the flux density is between ≈10-20 mJy at 5-700 GHz. Due to the inability of the model in previous studies to account for the newly added 100 GHz data point, we proceeded to update the models and make the necessary adjustments to the parameters. One possible interpretation of this broadband radio spectrum is a combination of emission from the jet base, the dusty torus, and the compact X-raying corona with the magnetic field strength of ≈20 G on scales of ≈30 Schwarzschild radii from the central black hole. In order to firmly identify the compact corona by omitting any other possible extended components (e.g., free-free emission from ionized gas around), high-resolution/sensitivity observations achieved by next-generation interferometers will be necessary.

Title: On the Zeeman Effect in Magnetically-Arrested Disks.
Authors: Yoshiyuki Inoue

Magnetically arrested disk (MAD) has been argued as the key accretion phase to realize the formation of relativistic jets. However, due to the lack of magnetic field measurements of accreting systems, MAD has not been observationally confirmed yet. Here we propose that a strong magnetic field accompanied by MAD would induce the Zeeman splitting of relativistically broadened Fe Kα fluorescence lines in X-ray binaries and active galactic nuclei, where we consider a two-phase medium in the inner accretion disk, magnetically dominated hot corona and cold reflector. Such a geometrical configuration is suggested from X-ray observations and recently confirmed by numerical simulations. Although turbulence in accretion flows would broaden the split lines, future X-ray high-energy resolution satellites, XRISM and Athena, would be capable of seeing the Zeeman effect on the Fe lines in X-ray binaries in the case with the MAD configuration. The signature of the Zeeman split lines would provide observational evidence for MAD.

Title: MeV Gamma-Ray Source Contribution to the Inner Galactic Diffuse Emission .
Authors: Naomi Tsuji, Yoshiyuki Inoue, Hiroki Yoneda, Reshmi Mukherjee, Hirokazu Odaka

The origin of the inner Galactic emission, measured by COMPTEL with a flux of ∼10−2 MeV cm−2 s−1 sr−1 in the 1-30 MeV energy range from the inner Galactic region, has remained unsettled since its discovery. In this paper, we elaborate on a model of individual MeV gamma-ray sources unresolved by COMPTEL. This is conducted for sources crossmatched between the Swift-BAT and Fermi-LAT catalogs by interpolating the energy spectra in the hard X-ray and GeV gamma-ray ranges, as well as unmatched sources between the two catalogs. We find that the source contribution to the COMPTEL emission would be at least ~20%. Combined with the Galactic diffuse emission, which is not well constrained, the COMPTEL emission can be roughly reproduced in some cases.

Title: ALMA Detection of Parsec-scale Blobs at the Head of a Kiloparsec-scale Jet in the Nearby Seyfert Galaxy NGC 1068.
Authors: Tomonari Michiyama, Yoshiyuki Inoue, Akihiro Doi, Dmitry Khangulyan We present Atacama Large Millimeter/submillimeter Array observations at ≈100 GHz with 0.05 arcsec (3 pc) resolution of the kiloparsec-scale jet seen in the nearby Seyfert galaxy NGC 1068, and we report the presence of parsec-scale blobs at the head of the jet. The combination of the detected radio flux (≈0.8 mJy), spectral index (≈0.5), and the blob size (≈10 pc) suggests a strong magnetic field of B≈240μG. Such a strong magnetic field most likely implies magnetic field amplification by streaming cosmic rays. The estimated cosmic-ray power by the jet may exceed the limit set by the star formation activity in this galaxy. This result suggests that even modest-power jets can increase the galactic cosmic-ray content while propagating through the galactic bulge.

Title: High energy emission component, population, and contribution to the extragalactic gamma-ray background of gamma-ray emitting radio galaxies.
Authors: Yasushi Fukazawa, Hiroto Matake, Taishu Kayanoki, Yoshiyuki Inoue, Justin Finke

In this study, we systematically studied the X-ray to GeV gamma-ray spectra of 61 {\it Fermi} Large Area Telescope (LAT) detected radio galaxies. We found an anticorrelation between peak frequency and peak luminosity in the high-energy spectral component of radio galaxies, similar to blazars. With this sample, we also constructed a gamma-ray luminosity function (GLF) of gamma-ray-loud radio galaxies. We found that blazar-like GLF shapes can reproduce their redshift and luminosity distribution, but the logN-logS relation prefers models with more low-z radio galaxies. This indicates many low-z gamma-ray-loud radio galaxies. By utilizing our latest GLF, the contribution of radio galaxies to the extragalactic gamma-ray background is found to be 1–10%. We further investigated the nature of gamma-ray-loud radio galaxies. Compared to radio or X-ray flux-limited radio galaxy samples, the gamma-ray selected sample tends to lack high radio power galaxies like FR-II radio galaxies. We also found that only ∼10% of radio galaxies are GeV gamma-ray loud. Radio galaxies may contribute to the cosmic MeV gamma-ray background comparable to blazars if gamma-ray-quiet radio galaxies have X-ray to gamma-ray spectra like Cen A, with a small gamma-ray to X-ray flux ratio.

Title: Interstellar Gas Heating by Primordial Black Holes.
Authors: Volodymyr Takhistov, Philip Lu, Graciela B. Gelmini, Kohei Hayashi, Yoshiyuki Inoue, Alexander Kusenko

Title: A fundamental plane in X-ray binary activity of external galaxies.
Authors: Yoshiyuki Inoue, Kiyoto Yabe, Yoshihiro Ueda

We construct a new catalog of extragalactic X-ray binaries (XRBs) by matching the latest Chandra source catalog with local galaxy catalogs. Our XRB catalog contains 4430 XRBs hosted by 237 galaxies within $\sim130$ Mpc. As XRBs dominate the X-ray activity in galaxies, the catalog enables us to study the correlations between the total X-ray luminosity of a galaxy, star formation rate, and stellar mass. We find that there is a fundamental plane in those three parameters. In order to investigate this relation, we construct a phenomenological binary population synthesis model. We find that the high mass XRB and low mass XRB fraction in formed compact object binary systems is $\sim 9$% and $\sim0.04$%, respectively. Utilizing the latest XMM-Newton, and Swift X-ray source catalog data sets, additional XRB candidates are also found resulting in 5757 XRBs hosted by 311 galaxies.

Title: Spatial variations of magnetic field along active galactic nuclei jets on sub-pc to Mpc scales.
Authors: Soichiro Ito, Yoshiyuki Inoue, Jun Kataoka

We report the systematic analysis of knots, hotspots, and lobes in 57 active galactic nuclei (AGNs) to investigate the variation of the magnetic field along with the jet from the sub-pc base to the terminus in kpc-to-Mpc scales. Expanding the number of radio/X-ray samples in \citet{2005ApJ…622..797K}, we analyzed the data in 12 FRI and 30 FRII radio galaxies, 12 quasars, and 3 BL Lacs that contained 76 knots, 42 hotspots, and 29 radio lobes. We first derived the equipartition magnetic fields in the cores and then estimated those in various jet components by assuming $B_{\rm est}$ $\propto$ $d^{-1}$, where $d$ is the distance from the jet base. On the other hand, the magnetic field in large-scale jets (knots, hotspots, and lobes), $B_{\rm eq}$, can be estimated from the observed flux and spatial extent under the equipartition hypothesis. We show that the magnetic field decreases as the distance along the jet increases, but generally gentler than $\propto d^{-1}$. The increase in $B_{\rm eq}/B_{\rm est}$ at a larger $d$ may suggest the deceleration of the jet around the downstream, but there is no difference between FRI and FRII jets. Moreover, the magnetic fields in the hotspots are systematically larger than those of knots and lobes. Finally, we applied the same analysis to knots and lobes in Centaurus~A to check whether the above discussion will hold even in a {\it single} jet source.

Title: Cross-match between the latest Swift-BAT and Fermi-LAT catalogs.
Authors: Naomi Tsuji, Hiroki Yoneda, Yoshiyuki Inoue, Tsuguo Aramaki, Georgia Karagiorgi, Reshmi Mukherjee, Hirokazu Odaka

We report the results of a cross-match study between the hard X-ray and GeV gamma-ray catalogs, by making use of the latest 105-month Swift-BAT and 10-yr Fermi-LAT catalogs, respectively. The spatial cross-matching between the two catalogs results in the matching of 132 point-like sources, including ~5% of false-match sources. Additionally, 24 sources that have been identified as the same identifications are matched. Among the 75 extended sources in the Fermi-LAT catalog, 31 sources have spatial coincidences with at least one Swift-BAT source inside their extent. All the matched sources consist of blazars (>60%), pulsars and pulsar wind nebulae (~13%), radio galaxies (~7%), binaries (~5%), and others. Compared to the original catalogs, the matched sources are characterized by a double-peaked photon index distribution, higher flux, and larger gamma-ray variability index. This difference arises from the different populations of sources, particularly the large proportion of blazars (i.e., FSRQ and BL Lac). We also report 13 cross-matched and unidentified sources. The matched sources in this study would be promising in the intermediate energy band between the hard X-ray and GeV gamma-ray observations, that is the unexplored MeV gamma-ray domain.

Title: Gamma-ray and Neutrino Signals from Accretion Disk Coronae of Active Galactic Nuclei.
Authors: Yoshiyuki Inoue, Dmitry Khangulyan, Akihiro Doi

To explain X-ray spectra of active galactic nuclei (AGN), non-thermal activity in AGN coronae such as pair cascade models has been extensively discussed in the past literature. Although X-ray and gamma-ray observations in the 1990s disfavored such pair cascade models, recent millimeter-wave observations of nearby Seyferts establish the existence of weak non-thermal coronal activity. Besides, the IceCube collaboration reported NGC 1068, a nearby Seyfert, as the hottest spot in their 10-yr survey. These pieces of evidence are enough to investigate the non-thermal perspective of AGN coronae in depth again. This article summarizes our current observational understandings of AGN coronae and describes how AGN coronae generate high-energy particles. We also provide ways to test the AGN corona model with radio, X-ray, MeV gamma-ray, and high-energy neutrino observations.