Old Posts

Title: Constraining Primordial Black Holes with Dwarf Galaxy Heating.
Authors: Philip Lu, Volodymyr Takhistov, Graciela B. Gelmini, Kohei Hayashi, Yoshiyuki Inoue, Alexander Kusenko

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 O(1)M_sun-10^7M_sun, relevant for the recently detected gravitational wave signals from intermediate-mass BHs.

Title: Origin of Galactic Spurs: New Insight from Radio/X-ray All-sky Maps.
Authors: Jun Kataoka, Marino Yamamoto, Yuki Nakamura, Soichiro Ito, Yoshiaki Sofue, Yoshiyuki Inoue, Takeshi Nakamori, Tomonori Totani

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.

Title: Follow-up Observations for IceCube-170922A: Detection of Rapid Near-Infrared Variability and Intensive Monitoring of TXS 0506+056.
Authors: Tomoki Morokuma, Yousuke Utsumi, Kouji Ohta, Masayuki Yamanaka, Koji S. Kawabata, Yoshiyuki Inoue, Masaomi Tanaka, Michitoshi Yoshida, Ryosuke Itoh, Mahito Sasada, Nozomu Tominaga, Hiroki Mori, Miho Kawabata, Tatsuya Nakaoka, Maiko Chogi, Taisei Abe, Ruochen Huang, Naoki Kawahara, Hiroki Kimura, Hiroki Nagashima, Kengo Takagi, Yuina Yamazaki, Wei Liu, Ryou Ohsawa, Shigeyuki Sako, Katsuhiro L. Murata, Kumiko Morihana, Christina K. Gilligan, Keisuke Isogai, Mariko Kimura, Yasuyuki Wakamatsu, Ryuhei Ohnishi, Masaki Takayama, Satoshi Honda, Yoshiki Matsuoka, Takuji Yamashita, Shigehiro Nagataki, Yasuyuki T. Tanaka

Now I am seeking a postdoctoral researcher at Osaka University. The candidate will work on the study of AGN coronal emission using theory, X-ray data, and radio (ALMA) data.

The position is posted here: https://jobregister.aas.org/ad/c9248b30

Application Deadline: Friday, November 13, 2020

活動銀河核コロナの研究に関する特任研究員(理論 and/or 観測)を一名、公募しております。 応募締切は令和2年11月13日(金) 日本時間 15:00必着です。 国立天文台で雇用され、大阪大学(豊中キャンパス)に派遣される形になります。

詳しくはこちらをご参照ください。 https://jobregister.nao.ac.jp/ja-JP/jobVacancyList https://www.nao.ac.jp/contents/job-vacancy/job-20201012-alma-osaka.pdf

興味のある方々からの積極的なご応募をお待ちしております。

質問等あれば、お気軽にお問い合わせください。

Title: Physical Conditions and Particle Acceleration in the Kiloparsec Jet of Centaurus A.
Authors: Takahiro Sudoh, Dmitry Khangulyan, Yoshiyuki Inoue

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 ($\eta_B\sim10^{-2}$) 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, $\eta_B\sim\eta_e\sim0.1$. 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.

朝日カルチャーセンター新宿教室の「宇宙の爆発現象シリーズ」第4回において、「巨大ブラックホールを通して紐解く宇宙の歴史」というタイトルで話しました。

Title: Blazar Radio and Optical Survey (BROS): A catalog of blazar candidates showing flat radio spectrum and their optical identification in Pan-STARRS1 Surveys.
Authors: Ryosuke Itoh, Yousuke Utsumi, Yoshiyuki Inoue, Kouji Ohta, Akihiro Doi, Tomoki Morokuma, Koji S. Kawabata, Yasuyuki T. Tanaka

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 $\delta>−40^\circ$ and outside the galactic plane ($|b|>10^\circ$). We list compact flat-spectrum radio sources of $\aloha>−0.6$ 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.

I renovate my website. Now it relys on Hugo. I adopt the Beautiful Hugo as the theme.

Title: Cosmological Evolution of FSRQs based on the Swift/BAT 105-month Catalog and Their Contribution to the Cosmic MeV Gamma-ray Background Radiation.
Authors: Koyo Toda, Yasushi Fukazawa, Yoshiyuki Inoue

We present a new X-ray luminosity function of flat-spectrum radio quasars (FSRQs) utilizing the latest 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∼1−2 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 ∼3% 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.