Research News

2019-03-12

Papers soon-to-be published in Nature Communications

A recent paper authored by several iTHEMS members has been accepted for publication in Nature Communications. The authors from iTHEMS include Hirotaka Ito (ABBL /iTHEMS), Shigehiro Nagataki (ABBL/iTHEMS) and Don Warren (iTHEMS). Congratulations! There will be a press release. Here is the explanation on the article by Hirataka Ito: "The photospheric origin of the Yonetoku relation in gamma-ray bursts” by Hirotaka Ito, Jin Matsumoto, Shigehiro Nagataki, Donald C. Warren, Maxim V. Barkov & Daisuke Yonetoku Accepted for publication in Nature Communications. arXiv:1806.00590 Gamma-ray bursts (GRBs), an intense flash of gamma-rays that is observed almost every day, are the brightest event in the Universe. Decades of studies have revealed that they are originating from a relativistic jet launched at the death of massive star. However, exactly how the gamma-rays are emitted from the jet is still veiled in mystery. One unresolved question is the origin of the correlation between the spectral peak energy and peak luminosity discovered in observations. This “Yonetoku relation” is the tightest correlation found in the properties of GRB emission, providing the best diagnostic for the emission mechanism. In this study, we focused on the so-called “photospheric emission” model which is one of the leading models for the emission mechanism of GRBs. To test the validity of the model, global dynamics of relativistic jet and radiation transfer must be taken into account. To tackle this issue, we performed three-dimensional relativistic hydrodynamical simulations and radiation transfer calculations to evaluate photospheric emission from relativistic jet that is breaking out of massive star envelope. Our simulations revealed that the Yonetoku relation is reproduced as a natural consequence of the jet-stellar interactions. This result strongly suggests that photospheric emission is the emission mechanism of GRBs.

2018-12-13

Di-Omega in QCD on the front page of an in-house magazine

Di-Omega in QCD reported in the previous iTHEMS NewsLetter became a front page of the latest news letter of "Science and technology companies pension fund". It is amazing that the pension fund organization is interested in elementary particle physics!

2018-11-08

Susumu Inoue (iTHEMS Research Scientist) was highlighted in a recent article of RIKEN RESEARCH "Highly energetic neutrino traced back to a blazar"

"The spectrum measured by MAGIC strongly points to the neutrino being generated by a high-energy proton in the blazar’s jet interacting with low-energy photons,” says Susumu Inoue of RIKEN’s Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS) program, who is part of the MAGIC team.

2018-10-11

X-ray telescope reveals the Milky Way’s halo of hot gas is fed by supernovae

The Milky Way is a spiral galaxy up to 100,000 light years across, and our Sun is just one of hundreds of billions of stars within it. The galaxy has a halo, which is partly made up of gas accumulated from the vast expanses of intergalactic space but is also molded and supplemented by matter ejected from the galaxy’s stars. The balance between these two sources is not fully understood, and there is ongoing debate about the halo’s size and shape. RIKEN Researchers have mapped this halo gas using the Suzaku X-ray telescope and revealed how exploding stars have helped to shape this blazing shroud.

2018-09-26

Tightening the noose on neutron star radii

The study by Oliver Just (Nagataki's lab.) and his collaborators in Germany and Greece has added much needed clarity to limiting the neutron star radius, a parameter that provides vital clues about the microphysics of neutron stars and hence also about the microphysics of nuclei on Earth. “Before our study, the radius of a neutron star was only weakly constrained from below,” Just says.

2018-09-10

Book on "Origins of the Gravitational Wave"

Kotaro Kyutoku (Assistant Prof. in KEK and iTHEMS visiting researcher. Former iTHEMS SPDR) has published a book "Origins of the Gravitational Wave" in Japanese with Masaru Shibata (Max Planck Institute and Kyoto Univ.). It contains excellent explanations on general relativity and black holes, structure of neutron stars, supernova explosion, gamma-ray burst, gravitational wave, mergers of black holes and neutron stars, and current/future gravitational wave detectors on earth and space. Everybody who is interested in GW should have one in his/her bookshelf. English translation will be called for.

2018-09-03

The Di-Omega Picture

The image of Di-Omega (an exotic particle with 6 strange quarks) was selected as the front page picture of the August issue of RIKEN NEWS (vol.446, 2018). This is based on the work done by HAL QCD Collaboration composed of 6 institutions (RIKEN Nishina Center, RIKEN iTHEMS, YITP in Kyoto Univ., CCS in Univ. Tsukuba, RCNP in Osaka Univ. and Nihon Univ.).

2018-07-17

High-energy neutrinos from a gamma-ray emitting supermassive black hole: the dawn of the electroweak sector of multi-messenger astronomy

Background: Since 2010, the IceCube Observatory, utilizing a cubic-km volume of ice in Antartica, has been detecting neutrinos with energies exceeding 100 TeV (~10^13 times the energy of a visible photon), which likely originate from astrophysical sources outside of the Milky Way Galaxy. However, their sources remained unknown, mainly due to the limited accuracy of their localizations in the sky. From 2016, IceCube initiated a new, automated alert program that rapidly identifies significant neutrino candidates and widely disseminates their sky positions, so that telescopes around the world can immediately search for potential counterparts at various wavelengths. Result: On September 22, 2017, a neutrino with energy ~300 TeV (dubbed IceCube-170922A) was detected with relatively good sky localization, and was rapidly followed up by numerous telescopes operating across the electromagnetic spectrum. The Fermi-LAT satellite and the MAGIC telescopes identified an object (named TXS 0506+056) shining brightly in gamma-rays (Fig. 1). The object is classified as a “blazar”, a type of supermassive black hole that is actively ejecting “jets" of plasma at relativistic velocities nearly toward us. This is the first time that a likely source of high-energy neutrinos has been identified with reasonable confidence [1]. These results were published in the July 13 issue of Science magazine, in a paper authored by more than 1100 scientits in 16 collaborations, including Susumu Inoue of iTHEMS as a member of the MAGIC Collaboration [2]. Implications: The production of such high-energy neutrinos requires the acceleration of hadrons (proton or nuclei) to extremely high energies. This implies special physical conditions in the jets from supermassive black holes, and offer valuable clues on the formation mechanism of the jets, which is not well understood. This may also be the first step in solving the long-standing mystery of the origin of ultra-high-energy cosmic rays, the highest energy particles known to exist in the Universe [3]. Finally, it may shed new light on the properties of neutrinos at energies far beyond the capability of terrestrial accelerator facilities. Prospects: Following on the heels of GW170817, the binary neutron star merger event discovered in August 2017 in gravitational waves and then identified in electromagnetic waves, this signals the dawn of the “electroweak" sector of multi-messenger astronomy involving neutrinos and photons. Vigorous efforts will continue in the next years, with bright prospects for elucidating the physics of supermassive black holes and their jets, the origin of high-energy neutrinos and cosmic rays, etc. Figure 1: Image of the sky at optical wavelengths of the region of interest. Overlayed are the positional uncertainties of the neutrino IceCube-170922A, and those of the blazar TXS 0506+056 at optical wavelengths and in gamma rays observed by Fermi and MAGIC.

2018-05-11

Shigehiro Nagataki (Deputy Program Director, iTHEMS) was featured in RIKEN NEWS, pp.02-05, No. 443 (2018 May issue) with the title "Why the massive stars explode?"

2017-12-18

An article about ithems was published in the RIKEN NEWS 2017 December p.10-13

2017-10-21

Masato Taki (Senior Research Scientist, iTHEMS) authored a new book on deep learning