arXiv subjects

Yoshiyuki Inoue

Publications and source records attributed to Yoshiyuki Inoue.

At least 55 records · Page 3Linked to original sources

arXiv2022

Spatially resolved study of the SS 433/W50 west region with Chandra: X-ray structure and spectral variation of non-thermal emission

The X-ray binary SS 433, embedded in the W50 nebula (or supernova remnant W50), shows bipolar jets that are ejected with mildly relativistic velocities, and extend toward the east and west out to scales of tens of parsecs. Previous X-ray observations revealed twin lobes along the jet precession axis that contain compact bright knots dominated by synchrotron radiation, which provide evidence of electron acceleration in this system. Particle acceleration in this system is substantiated by the recently detected gamma rays with energies up to at least 25 TeV. To further elucidate the origin of the knots and particle acceleration sites in SS 433/W50, we report here on detailed, spatially resolved X-ray spectroscopy of its western lobe with Chandra. We detect synchrotron emission along the jet precession axis, as well as optically thin thermal emission that is more spatially extended. Between the two previously known knots, w1 and w2, we discover another synchrotron knot, which we call w1.5. We find no significant synchrotron emission between SS 433 and the innermost X-ray knot (w1), suggesting that electrons only begin to be accelerated at w1. The X-ray spectra become gradually steeper from w1 to w2, and then rapidly so immediately outside of w2. Comparing with a model taking into account electron transport and cooling along the jet, this result indicates that the magnetic field in w2 is substantially enhanced, which also explains its brightness. We discuss possible origins of the enhanced magnetic field of w2 as well as scenarios to explain the other two knots.

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arXiv2022

Event reconstruction of Compton telescopes using a multi-task neural network

We have developed a neural network model to perform event reconstruction of Compton telescopes. This model reconstructs events that consist of three or more interactions in a detector. It is essential for Compton telescopes to determine the time order of the gamma-ray interactions and whether the incident photon deposits all energy in a detector or it escapes from the detector. Our model simultaneously predicts these two essential factors using a multi-task neural network with three hidden layers of fully connected nodes. For verification, we have conducted numerical experiments using Monte Carlo simulation, assuming a large-area Compton telescope using liquid argon to measure gamma rays with energies up to $3.0\,\mathrm{MeV}$. The reconstruction model shows excellent performance of event reconstruction for multiple scattering events that consist of up to eight hits. The accuracies of hit order prediction are around $60\%$ while those of escape flags are higher than $70\%$ for up to eight-hit events of $4π$ isotropic photons. Compared with two other algorithms, a classical model and a physics-based probabilistic one, the present neural network method shows high performance in estimation accuracy particularly when the number of scattering is small, 3 or 4. Since simulation data easily optimize the network model, the model can be flexibly applied to a wide variety of Compton telescopes.

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arXiv2022

Interstellar Gas Heating by Primordial Black Holes

Interstellar gas heating is a powerful cosmology-independent observable for exploring the parameter space of primordial black holes (PBHs) formed in the early Universe that could constitute part of the dark matter (DM). We provide a detailed analysis of the various aspects for this observable, such as PBH emission mechanisms. Using observational data from the Leo T dwarf galaxy, we constrain the PBH abundance over a broad mass-range, $M_{\rm PBH} \sim \mathcal{O}(1) M_{\odot}-10^7 M_{\odot}$, relevant for the recently detected gravitational wave signals from intermediate-mass BHs. We also consider PBH gas heating of systems with bulk relative velocity with respect to the DM, such as Galactic clouds.

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arXiv2022

High energy emission component, population, and contribution to the extragalactic gamma-ray background of gamma-ray emitting radio galaxies

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 log$N$-log$S$ 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 $\sim$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.

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arXiv2022

Advancing the Landscape of Multimessenger Science in the Next Decade

The last decade has brought about a profound transformation in multimessenger science. Ten years ago, facilities had been built or were under construction that would eventually discover the nature of objects in our universe could be detected through multiple messengers. Nonetheless, multimessenger science was hardly more than a dream. The rewards for our foresight were finally realized through IceCube's discovery of the diffuse astrophysical neutrino flux, the first observation of gravitational waves by LIGO, and the first joint detections in gravitational waves and photons and in neutrinos and photons. Today we live in the dawn of the multimessenger era. The successes of the multimessenger campaigns of the last decade have pushed multimessenger science to the forefront of priority science areas in both the particle physics and the astrophysics communities. Multimessenger science provides new methods of testing fundamental theories about the nature of matter and energy, particularly in conditions that are not reproducible on Earth. This white paper will present the science and facilities that will provide opportunities for the particle physics community renew its commitment and maintain its leadership in multimessenger science.

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arXiv2021

Impacts of Jets and Winds From Primordial Black Holes

Primordial black holes (PBHs) formed in the early Universe constitute an attractive candidate for dark matter. Within the gaseous environment of the interstellar medium, PBHs with accretion disks naturally launch outflows such as winds and jets. PBHs with significant spin can sustain powerful relativistic jets and generate associated cocoons. Jets and winds can efficiently deposit their kinetic energies and heat the surrounding gas through shocks. Focusing on the Leo T dwarf galaxy, we demonstrate that these considerations can provide novel tests of PBHs over a significant $\sim 10^{-2} M_{\odot} - 10^6 M_{\odot}$ mass range, including the parameter space associated with gravitational wave observations by the LIGO and VIRGO Collaborations. Observing the morphology of emission could allow to distinguish between jet and wind contributions, and hence indirectly detect spinning PBHs.

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arXiv2021

A Fundamental Plane in X-ray Binary Activity of External Galaxies

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 ~130 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 $L_{X,\rm tot}$, star formation rate $\dotρ_\star$, and stellar mass $M_\star$. As previously reported, $L_{X,\rm tot}$ is correlated with $\dotρ_\star$ and $M_\star$. In particular, we find that there is a fundamental plane in those three parameters as $\log L_{X,\rm tot}={38.80^{+0.09}_{-0.12}}+\log(\dotρ_\star + αM_\star)$, where $α= {(3.36\pm1.40)\times10^{-11}}\ {\rm yr^{-1}}$. 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 ~9% and ~0.04%, 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.

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arXiv2021

Spatial variations of magnetic field along active galactic nuclei jets on sub-pc to Mpc scales

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 Kataoka & Stawarz (2005), we analyzed the data in 12 FR I and 30 FR II 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 FR I and FR II 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 single jet source.

astro-ph.GA↗

arXiv2021

Cross-match between the latest Swift-BAT and Fermi-LAT catalogs

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.

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arXiv2021

Gamma-ray and Neutrino Signals from Accretion Disk Coronae of Active Galactic Nuclei

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.

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arXiv2021

Constraining Primordial Black Holes with Dwarf Galaxy Heating

Black holes formed in the early universe, prior to the formation of stars, can exist as dark matter and also contribute to the black hole merger events observed in gravitational waves. We set a new limit on the abundance of primordial black holes (PBHs) by considering interactions of PBHs with the interstellar medium, which result in the heating of gas. We examine generic heating mechanisms, including emission from the accretion disk, dynamical friction, and disk outflows. Using the data from the Leo T dwarf galaxy, we set a new cosmology-independent limit on the abundance of PBHs in the mass range $\mathcal{O}(1) M_{\odot}-10^7 M_{\odot}$, relevant for the recently detected gravitational wave signals from intermediate-mass BHs.

astro-ph.CO↗

arXiv2021

Origin of Galactic Spurs: New Insight from Radio/X-ray All-sky Maps

In this study, we analyze giant Galactic spurs seen in both radio and X-ray all-sky maps to reveal their origins. We discuss two types of giant spurs: one is the brightest diffuse emission near the map's center, which is likely to be related to Fermi bubbles (NPSs/SPSs, north/south polar spurs, respectively), and the other is weaker spurs that coincide positionally with local spiral arms in our Galaxy (LAS, local arm spur). Our analysis finds that the X-ray emissions, not only from the NPS but from the SPS are closer to the Galactic center by ~5 deg compared with the corresponding radio emission. Furthermore, larger offsets of 10-20 deg are observed in the LASs; however, they are attributed to different physical origins. Moreover, the temperature of the X-ray emission is kT ~ 0.2 keV for the LAS, which is systematically lower than those of the NPS and SPS (kT ~ 0.3 keV) but consistent with the typical temperature of Galactic halo gas. We argue that the radio/X-ray offset and the slightly higher temperature of the NPS/SPS X-ray gas are due to the shock compression/heating of halo gas during a significant Galactic explosion in the past, whereas the enhanced X-ray emission from the LAS may be due to the weak condensation of halo gas in the arm potential or star formation activity without shock heating.

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arXiv2020

Follow-up Observations for IceCube-170922A: Detection of Rapid Near-Infrared Variability and Intensive Monitoring of TXS 0506+056

We present our follow-up observations to search for an electromagnetic counterpart of the IceCube high-energy neutrino, IceCube-170922A. Monitoring observations of a likely counterpart, TXS 0506+056, are also described. First, we quickly took optical and near-infrared images of 7 flat-spectrum radio sources within the IceCube error region right after the neutrino detection and found a rapid flux decline of TXS 0506+056 in Kanata/HONIR J-band data. Motivated by this discovery, intensive follow-up observations of TXS 0506+056 are continuously done, including our monitoring imaging observations, spectroscopic observations, and polarimetric observations in optical and near-infrared wavelengths. TXS 0506+056 shows a large amplitude (~1.0 mag) variability in a time scale of several days or longer, although no significant variability is detected in a time scale of a day or shorter. TXS 0506+056 also shows a bluer-when-brighter trend in optical and near-infrared wavelengths. Structure functions of variabilities are examined and indicate that TXS 0506+056 is not a special blazar in terms of optical variability. Polarization measurement results of TXS 0506+056 are also discussed.

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arXiv2020

Snowmass 2021 Letter of Interest: The GRAMS Project: MeV Gamma-Ray Observations and Antimatter-Based Dark Matter Searches

The Gamma-Ray and AntiMatter Survey (GRAMS) project is a proposed next-generation balloon/satellite mission targeting both MeV gamma-ray observations and antimatter-based dark matter searches. A cost-effective, large-scale Liquid Argon Time Projection Chamber (LArTPC) detector technology will allow GRAMS to have a significantly improved sensitivity to MeV gamma rays while extensively probing dark matter parameter space via antimatter measurements.

astro-ph.HE↗

arXiv2020

Physical Conditions and Particle Acceleration in the Kiloparsec Jet of Centaurus A

The non-thermal emission from the kiloparsec-scale jet of Centaurus A exhibits two notable features, bright diffuse emission and many compact knots, which have been intensively studied in X-ray and radio observations. H.E.S.S. recently reported that the very-high-energy gamma-ray emission from this object is extended along the jet direction beyond a kiloparsec from the core. Here, we combine these observations to constrain the physical conditions of the kpc-jet and study the origin of the non-thermal emission. We show that the diffuse jet is weakly magnetized ($η_B\sim10^{-2}$) and energetically dominated by thermal particles. We also show that knots are the sites of both amplified magnetic field and particle (re-)acceleration. To keep sufficient energy in thermal particles, the magnetic and non-thermal particle energy in the knot regions are tightly constrained. The most plausible condition is an energy equipartition between them, $η_B\simη_e\sim0.1$. Such weak magnetic energy implies that particles in the knots are in the slow cooling regime. We suggest that the entire kpc-scale diffuse emission could be powered by particles that are accelerated at and escaped from knots.

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arXiv2020

Blazar Radio and Optical Survey (BROS): A catalog of blazar candidates showing flat radio spectrum and their optical identification in Pan-STARRS1 Surveys

Utilizing the latest and the most sensitive radio and optical catalogs, we completed a new blazar candidate catalog, Blazar Radio and Optical Survey (BROS), which includes 88,211 sources located at declination $δ> -40^{\circ}$ and outside the galactic plane ($|b| > 10^{\circ}$). We list compact flat-spectrum radio sources of $α> -0.6$ ($α$ is defined as $F_ν \propto ν^α$ ) from 0.15~GHz TGSS and 1.4~GHz NVSS catalogs. We further identify optical counterparts of the selected sources by cross-matching with Pan-STARRS1 photometric data. Color-color and color-magnitude plots for the selected BROS sources clearly show two distinct populations, An "quasar-like" population consisting of both flat-spectrum radio quasars and BL Lac type objects. On the other hand, an "elliptical-like" population of mostly BL Lac-type objects is buried in the elliptical galaxy. We emphasize that the latter population is missed by previous catalogs but newly emerged in the present BROS catalog, due to the lower radio flux threshold of our selection. Model calculations show that the "elliptical-like" population consists of elliptical galaxies located at redshift z $\lesssim$ 0.5, which is also supported by the logN-logS distribution of the power-law index of $1.49 \pm 0.05$. This BROS catalog is useful for identifying the electromagnetic counterparts of ultra-high-energy cosmic rays and PeV neutrinos recently detected by IceCube, as well as nearby BL Lac objects detectable by future high sensitivity TeV telescopes, such as Cherenkov Telescope Array.

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arXiv2020

Cosmological Evolution of Flat-Spectrum Radio Quasars based on the {\it Swift}/BAT 105-month Catalog and Their Contribution to the Cosmic MeV Gamma-ray Background Radiation

We present a new X-ray luminosity function of flat-spectrum radio quasars (FSRQs) utilizing the latest {\it Swift}/BAT 105-month X-ray source catalog. Contrary to previous studies of FSRQs in the X-ray band, using the luminosity-dependent density evolution model, we find that FSRQs show evolutionary peaks at $z\sim1-2$ depending on luminosities. Our result is rather consistent with the evolution of FSRQs seen in the radio and GeV bands, although the number density is a factor of 5--10 smaller. We further explore the contribution of FSRQs to the cosmic MeV gamma-ray background radiation. We find that FSRQs can explain only $\sim3$\% of the observed MeV gamma-ray background fluxes around 1 MeV, indicating other populations are required. Future MeV gamma-ray observations will be keys for understanding the origin of the MeV gamma-ray background radiation.

astro-ph.HE↗

arXiv2020

On the Origin of High Energy Neutrinos from NGC 1068: The Role of Non-Thermal Coronal Activity

NGC 1068, a nearby type-2 Seyfert galaxy, is reported as the hottest neutrino spot in the 10-year survey data of IceCube. Although there are several different possibilities for the generation of high-energy neutrinos in astrophysical sources, feasible scenarios allowing such emission in NGC 1068 have not yet been firmly defined. We show that the flux level of GeV and neutrino emission observed from NGC 1068 implies that the neutrino emission can be produced only in the vicinity of the supermassive black hole in the center of the galaxy. The coronal parameters, such as magnetic field strength and corona size, making this emission possible are consistent with the spectral excess registered in the millimeter range. The suggested model and relevant physical parameters are similar to those revealed for several nearby Seyferts. Due to the internal gamma-ray attenuation, the suggested scenario cannot be verified by observations of NGC 1068 in the GeV and TeV gamma-ray energy bands. However, the optical depth is expected to become negligible for MeV gamma rays, thus future observations in this band will be able to prove our model.

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