Papers by Shigehiro Nagataki
The Astrophysical Journal
For several decades, the origin of ultra-high-energy cosmic rays (UHECRs) has been an unsolved qu... more For several decades, the origin of ultra-high-energy cosmic rays (UHECRs) has been an unsolved question of high-energy astrophysics. One approach for solving this puzzle is to correlate UHECRs with high-energy neutrinos, since neutrinos are a direct probe of hadronic interactions of cosmic rays and are not deflected by magnetic fields. In this paper, we present three different approaches for correlating the arrival directions of neutrinos with the arrival directions of UHECRs. The neutrino data are provided by the IceCube Neutrino Observatory and ANTARES, while the UHECR data with energies above ∼50 EeV are provided by the Pierre Auger Observatory and the Telescope Array. All experiments provide increased statistics and improved reconstructions with respect to our previous results reported in 2015. The first analysis uses a high-statistics neutrino sample optimized for point-source searches to search for excesses of neutrino clustering in the vicinity of UHECR directions. The second...
arXiv (Cornell University), Aug 31, 2001
We estimate the fluxes of very high energy (VHE) gamma-rays and neutrinos from the Galactic Cente... more We estimate the fluxes of very high energy (VHE) gamma-rays and neutrinos from the Galactic Center which are by-products of the hadronic interactions between primary protons which are accelerated up to ∼ 10 19 eV and ambient matter. We find that these signals depend strongly on the spectrum index of the primary protons. This means that detection of these signals from the Galactic Center will constrain the spectrum of the primary particles, which, in turn, should constrain the acceleration mechanism at the Galactic Center. We show that GeV-TeV gamma-rays will be detected by the ground-based Cherenkov telescopes such as CANGAROOIII and the next-generation satellites such as GLAST. Thus the acceleration region of the CRs below ∼ 10 19 eV will be determined accurately by gamma-ray telescopes, which should help our understanding on the particle acceleration. We estimate the event rate of VHE neutrinos for the planned 1 km 2 detectors such as IceCube, ANTARES and NESTOR. The event rate also depends on the spectrum index of the primary protons. In the optimistic case, the event rate amounts to ∼ 10 4 events per year and the signals from the Galactic Center dominate the atmospheric neutrino background.
In this paper, simulations of propagation of UHE-protons from nearby galaxies are presented. We f... more In this paper, simulations of propagation of UHE-protons from nearby galaxies are presented. We found good parameter sets to explain the arrival distribution of UHECRs reported by AGASA and the energy spectrum reported by HiRes. Using a good parameter set, we demonstrated what distribution of arrival direction of UHECRs will be as a function of event numbers. We show that 1000-10000 events are necessary to clearly see the source distribution. We also showed that effects of interactions and trapping of UHE-Nuclei in a galaxy cluster are very important. Especially, when a UHECR source is a bursting source such as a GRB/AGN flare, heavy UHE-Nuclei are trapped for a long time in the galaxy cluster, which changes the spectrum and chemical composition of UHECRs coming from the galaxy cluster. We also showed that such effects can be important when there have been sources of UHE-Nuclei in the Milky Way. Since light nuclei escape from the Milky Way in a short timescale, the chemical composit...
Journal of Physics: Conference Series, 2020
We present the results of a search for point sources of photons with energies higher than 1 EeV b... more We present the results of a search for point sources of photons with energies higher than 1 EeV based on the Telescope Array surface detector data for 9 years. No significant excess of photon signal over UHECR background was found. The photon-flux upper limits were set for each direction in the Telescope Array field of view as well as for stacked directions of dwarf spheroidal galaxies.
Publications of the Astronomical Society of Japan, 2021
We present our follow-up observations to search for an electromagnetic counterpart of the IceCube... more 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 seven 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 were continuously performed, including our monitoring imaging observations, spectroscopic observations, and polarimetric observations in optical and near-infrared wavelengths. TXS 0506+056 showed a large-amplitude (∼1.0 mag) variability in a time scale of several days or longer, although no significant variability was detected in a time scale of a day or shorter. TXS 0506+056 also showed a bluer-when-brighter trend in optical and near-infrared wavelengths. Str...
ЖУРНАЛ ЭКСПЕРИМЕНТАЛЬНОЙ И ТЕОРЕТИЧЕСКОЙ ФИЗИКИ, 2020
R. U. Abbasi , M. Abe , T. Abu-Zayyad , M. Allen , R. Azuma , E. Barcikowski , J. W. Belz , D. R.... more R. U. Abbasi , M. Abe , T. Abu-Zayyad , M. Allen , R. Azuma , E. Barcikowski , J. W. Belz , D. R. Bergman , S. A. Blake , R. Cady , B. G. Cheon , J. Chiba , M. Chikawa , A. di Matteo , T. Fujii , K. Fujita , R. Fujiwara , M. Fukushima , G. Furlich , W. Hanlon , M. Hayashi , Y. Hayashi , N. Hayashida , K. Hibino , K. Honda , D. Ikeda , N. Inoue , T. Ishii , R. Ishimori , H. Ito , D. Ivanov , H. M. Jeong , S. Jeong , C. C. H. Jui , K. Kadota , F. Kakimoto , O. Kalashev , K. Kasahara , H. Kawai , S. Kawakami , S. Kawana , K. Kawata , E. Kido , H. B. Kim , J. H. Kim , J. H. Kim , S. Kishigami , S. Kitamura , Y. Kitamura , V. Kuzmin , M. Kuznetsov , Y. J. Kwon , K. H. Lee , B. Lubsandorzhiev , J. P. Lundquist , K. Machida , K. Martens , T. Matsuyama , J. N. Matthews , R. Mayta , M. Minamino , K. Mukai , I. Myers , K. Nagasawa , S. Nagataki , K. Nakai , R. Nakamura , T. Nakamura , T. Nonaka , H. Oda , S. Ogio , J. Ogura , M. Ohnishi , H. Ohoka , T. Okuda , Y. Omura , M. Ono , R. Onogi , A. Oshima , S. Ozawa , I. H. Park , M. S. Pshirkov , J. Remington , D. C. Rodriguez , G. Rubtsov , D. Ryu , H. Sagawa , R. Sahara , K. Saito , Y. Saito , N. Sakaki , T. Sako , N. Sakurai , L. M. Scott , T. Seki , K. Sekino , P. D. Shah , F. Shibata , T. Shibata , H. Shimodaira , B. K. Shin , H. S. Shin , J. D. Smith , P. Sokolsky , B. T. Stokes , S. R. Stratton , T. A. Stroman , T. Suzawa , Y. Takagi , Y. Takahashi , M. Takamura , M. Takeda , R. Takeishi , A. Taketa , M. Takita , Y. Tameda , H. Tanaka , K. Tanaka , M. Tanaka , Y. Tanoue , S. B. Thomas , G. B. Thomson , P. Tinyakov , I. Tkachev , H. Tokuno , T. Tomida , S. Troitsky , Y. Tsunesada , K. Tsutsumi , Y. Uchihori , S. Udo , F. Urban , T. Wong , K. Yada , M. Yamamoto , H. Yamaoka , K. Yamazaki , J. Yang , K. Yashiro , H. Yoshii , Y. Zhezher a*, Z. Zundel a a Authors and Affiliations see below Поступила в редакцию 9 мая 2019 г., после переработки 24 января 2020 г. Принята к публикации 29 января 2020 г.
Proceedings of Gamma-Ray Bursts 2012 Conference — PoS(GRB 2012), 2012
I have developed 2-and 3-dimensional general relativistic magnetohydrodynamic (GRMHD) code. I per... more I have developed 2-and 3-dimensional general relativistic magnetohydrodynamic (GRMHD) code. I performed numerical simulations of collapsars using these codes and realistic progenitor models. In the GRMHD simulation, it was shown that a jet is launched from the central region of the progenitor as long as the central black hole is rotating rapidly. I performed simulations of collapsars with different Kerr parameters a= 0, 0.5, 0.9, 0.95. It is shown that a more rapidly rotating black hole is driving a more energetic jet. No jet is seen for the case of Schwartzschild black hole case, while the total energy of the jet is as large as 10 50 erg for a rapidly rotating Kerr black hole case (a=0.95). In order to explain the high luminosity of a GRB, it is concluded that a rapidly rotating black hole is favored ('faster is better'). I also started to perform 3-dimensional GRMHD simulation of collapsars.
The Astrophysical Journal, 2018
The Telescope Array observatory utilizes fluorescence detectors and surface detectors to observe ... more The Telescope Array observatory utilizes fluorescence detectors and surface detectors to observe air showers produced by ultra high energy cosmic rays in the Earth's atmosphere. Cosmic ray events observed in this way are termed hybrid data. The depth of air shower maximum is related to the mass of the primary particle that generates the shower. This paper reports on shower maxima data collected over 8.5 years using the Black Rock Mesa and Long Ridge fluorescence detectors in conjunction with the array of surface detectors. We compare the means and standard deviations of the observed X max distributions with Monte Carlo X max distributions of unmixed protons, helium, nitrogen, and iron, all generated using the QGSJet II-04 hadronic model. We also perform an unbinned maximum likelihood test of the observed data, which is subjected to variable systematic shifting of the data X max distributions to allow us to test the full distributions, and compare them to the Monte Carlo to see which elements are not compatible with the observed data. For all energy bins, QGSJet II-04 protons are found to be compatible with Telescope Array hybrid data at the 95% confidence level after some systematic X max shifting of the data. Three other QGSJet II-04 elements 3 are found to be compatible using the same test procedure in an energy range limited to the highest energies where data statistics are sparse.
Brazilian Journal of Physics, 2014
Highlights from the Telescope Array experiment Grigory I. Rubtsov a, * on behalf of the Telescope... more Highlights from the Telescope Array experiment Grigory I. Rubtsov a, * on behalf of the Telescope Array Collaboration †
Journal of Cosmology and Astroparticle Physics, 2016
This paper presents the results of different searches for correlations between very high-energy n... more This paper presents the results of different searches for correlations between very high-energy neutrino candidates detected by IceCube and the highest-energy cosmic rays measured by the Pierre Auger Observatory and the Telescope Array. We first consider samples of cascade neutrino events and of high-energy neutrino-induced muon tracks, which provided evidence for a neutrino flux of astrophysical origin, and study their cross-correlation with the ultrahigh-energy cosmic ray (UHECR) samples as a function of angular separation. We also study their possible directional correlations using a likelihood method stacking the neutrino arrival directions and adopting different assumptions on the size of the UHECR magnetic deflections. Finally, we perform another likelihood analysis stacking the UHECR directions and using a sample of through-going muon tracks optimized for neutrino point-source searches with sub-degree angular resolution. No indications of correlations at discovery level are obtained for any of the searches performed. The smallest of the p-values comes from the search for correlation between UHECRs with IceCube high-energy cascades, a result that should continue to be monitored.
The Telescope Array (TA) collaboration has reported a hotspot, a cluster of 19 cosmic ray events ... more The Telescope Array (TA) collaboration has reported a hotspot, a cluster of 19 cosmic ray events with energies above $57$ EeV in a circle of $20^\circ$ radius centered at ${\rm R.A.}(\alpha)=146.^\circ7$, ${\rm Dec.}(\delta)=43.^\circ2$. We explore the hypothesis that the hotspot could originate from a single source. By considering the energy dependent deflections that are expected to affect arrival directions of cosmic rays propagating in cosmic magnetic fields, we identify the nearby starburst galaxy M82 and the bright nearby blazar Mrk 180 as two likely candidates. Furthermore, we constrain these hotspot cosmic rays to be light nuclei by adopting a specific magnetic field in the supergalactic plane. We discuss the prospects of discriminating between the candidate sources with current and future spectral data.
All-sky Survey High Resolution Air-shower telescope project, ASHRA, is newly proposed internation... more All-sky Survey High Resolution Air-shower telescope project, ASHRA, is newly proposed international joint collaboration efforts. ASHRA is designed to detect three different high energy particle species, i.e., high energy gamma rays (> 1TeV), very high energy cosmic rays (> 10 18 eV) and high energy neutrinos (> 10 16 eV). Here we discuss impacts on astrophysics to measure these particle species.
The Astrophysical Journal, 2003
We predict the arrival distribution of UHECRs above 4 × 10 19 eV with the event number expected b... more We predict the arrival distribution of UHECRs above 4 × 10 19 eV with the event number expected by future experiments in the next few years. We perform event simulations with the source model which is adopted in our recent study and can explain the current AGASA observation. At first, we calculate the harmonic amplitude and the two point correlation function for the simulated event sets. We find that significant anisotropy on large angle scale will be observed when ∼ 10 3 cosmic rays above 4 × 10 19 eV are detected by future experiments. The Auger array will detect cosmic rays with this event number in a few years after its operation. The statistics of the two point correlation function will also increase. The angle scale at which the events have strong correlation with each other corresponds to deflection angle of UHECR in propagating in the EGMF, which in turn can be determined by the future observations. We further investigate the relation between the number of events clustered at a direction and the distance of their sources. Despite the limited amount of data, we find that the C2 triplet events observed by the AGASA may originate from the source within 100 Mpc from us at 2σ confidence level. Merger galaxy Arp 299 (NGC 3690 + IC 694) is the best candidate for their source. If data accumulate, the UHECR sources within ∼ 100 Mpc can be identified from observed event clusterings significantly. This will provide some kinds of information about poorly known parameters which influence the propagation of UHECRs, such as extragalactic and galactic magnetic field, chemical composition of observed cosmic rays. Also, we will reveal their origin with our method to identify the sources of UHECR. Finally, we predict the arrival distribution of UHECRs above 10 20 eV, which is expected to be observed if the current HiRes spectrum is correct, and discuss their statistical features and implications.
The Astrophysical Journal, 2007
Regenerated high-energy emissions from gamma-ray bursts (GRBs) are studied in detail. If the intr... more Regenerated high-energy emissions from gamma-ray bursts (GRBs) are studied in detail. If the intrinsic primary spectrum extends to the TeV range, these very high-energy photons are absorbed by the cosmic infrared background (CIB). Created high-energy electron-positron pairs up-scatter mainly cosmic microwave background (CMB) photons, and secondary photons are generated in the GeV-TeV range. These secondary delayed photons may be observed in the near future, which are useful for a consistency check of the intrinsic primary spectrum. In this paper, we focus on effects of the CIB on delayed secondary emissions. In particular, we show that not only up-scattered CMB photons but also up-scattered CIB ones are important, especially for low redshift bursts. They also give us additional information on the CIB, whose photon density is not definitely determined so far.
The Astrophysical Journal, 2006
We simulate neutrino production in a gamma-ray burst (GRB) with the most detailed method to date.... more We simulate neutrino production in a gamma-ray burst (GRB) with the most detailed method to date. We show that the highest energy neutrinos from GRBs mainly come from kaons. Although there is little chance to detect such neutrinos, attempts of detection are very important to prove physical conditions in GRBs.
The Astrophysical Journal, 2004
Recently, the High Resolution Fly's Eye (HiRes) experiment claims that there is no small scale an... more Recently, the High Resolution Fly's Eye (HiRes) experiment claims that there is no small scale anisotropy in the arrival distribution of ultra-high energy cosmic rays (UHECRs) above E > 10 19 eV contrary to the Akeno Giant Air Shower Array (AGASA) observation. In this paper, we discuss the statistical significance of this discrepancy between the two experiments. We calculate arrival distribution of UHECRs above 10 19 eV predicted by the source models constructed using the Optical Redshift Survey galaxy sample. We apply the new method developed by us for calculating arrival distribution in the presence of the galactic magnetic field. The great advantage of this method is that it enables us to calculate UHECR arrival distribution with lower energy (∼ 10 19 eV) than previous studies within reasonable time by following only the trajectories of UHECRs actually reaching the earth. It has been realized that the small scale anisotropy observed by the AGASA can be explained with the source number density ∼ 10 −5∼−6 Mpc −3 assuming weak extragalactic magnetic field (B ≤ 1 nG). We find that the predicted small scale anisotropy for this source number density is also consistent with the current HiRes data. We thus conclude that the statement by the HiRes experiment that they do not find small scale anisotropy in UHECR arrival distribution is not statistically significant at present. We also show future prospect of determining the source number density with increasing amount of observed data.
The Astrophysical Journal, 2008
In this paper we perform a new estimate of the high energy neutrinos expected from GRBs associate... more In this paper we perform a new estimate of the high energy neutrinos expected from GRBs associated with the first generation of stars in light of new models and constraints on the epoch of reionization and a more detailed evaluation of the neutrino emission yields. We also compare the diffuse high energy neutrino background from Population III stars with the one from "ordinary stars" (Population II), as estimated consistently within the same cosmological and astrophysical assumptions. In disagreement with previous literature, we find that high energy neutrinos from Population III stars will not be observable with current or near future neutrino telescopes, falling below both IceCube sensitivity and atmospheric neutrino background under the most extreme assumptions for the GRB rate. This rules them out as a viable diagnostic tool for these still elusive metal-free stars.
The Astrophysical Journal, 2003
We present numerical simulations on the propagation of UHE protons with energies of (10 19.5 − 10... more We present numerical simulations on the propagation of UHE protons with energies of (10 19.5 − 10 22) eV in extragalactic magnetic fields over 1 Gpc. We use the ORS galaxy sample, which allow us to accurately quantify the contribution of nearby sources to the energy spectrum and the arrival distribution, as a source model. The sample is corrected taking the selection effect and absence of galaxies in the zone of avoidance (|b| < 20 •) into account. We calculate three observable quantities, cosmic ray spectrum, harmonic amplitude, and two point correlation function from our data of numerical simulations. With these quantities, we compare the results of our numerical calculations with the observation. We find that the arrival distribution of UHECRs become to be most isotropic as restricting sources to luminous galaxies (M lim = −20.5). However, it is not isotropic enough to be consistent with the AGASA observation, even for M lim = −20.5. In order to obtain sufficiently isotropic arrival distribution, we randomly select sources, which contribute to the observed cosmic ray flux, from the ORS sample more luminous than −20.5 mag, and investigate dependence of the results on their number. We show that the three observable quantities including the GZK cutoff of the energy spectrum can be reproduced in the case that the number fraction ∼ 10 −1.7 of the ORS galaxies more luminous than −20.5 mag is selected as UHECR sources. In terms of the source number density, this constraint corresponds to ∼ 10 −6 Mpc −3. However, since mean number of sources within the GZK sphere is only ∼ 0.5 in this case, the AGASA 8 events above 10 20.0 eV, which do not constitute the clustered events with each other, can not be reproduced. On the other hand, if the cosmic ray flux measured by the HiRes, which is consistent with the GZK cutoff, is correct and observational features about the arrival distribution of UHECRs are same as the AGASA, our source model can explain both the arrival distribution and the flux at the same time. Thus, we conclude that large fraction of the AGASA 8 events above 10 20 eV might originate in the topdown scenarios, or that the cosmic ray flux measured by the HiRes experiment might be better. We also discuss the origin of UHECRs below 10 20.0 eV through comparisons between the number density of astrophysical source candidates and our result (∼ 10 −6 Mpc −3).
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Papers by Shigehiro Nagataki