arXiv subjects

M. Ohno

Publications and source records attributed to M. Ohno.

At least 19 recordsLinked to original sources

arXiv2023

Impact of iso-structural template layer on stabilizing pyrochlore Bi$_2$Rh$_2$O$_7$

We present an epitaxial stabilization of pyrochlore Bi$_2$Rh$_2$O$_7$ on Y-stabilized ZrO$_2$ (YSZ) (111) substrate by inserting a pyrochlore Eu$_2$Ti$_2$O$_7$ template layer, otherwise Bi-based layered structures being formed directly on YSZ (111) substrate. This result reveals that "iso-structural crystal phase" plays an important role in the interfacial phase control. The Bi$_2$Rh$_2$O$_7$ film exhibits $p$-type electrical conduction with the lowest longitudinal resistivity ($\rho_\mathrm{xx}$) among the reported Rh pyrochlore oxides. Such parameters as $\rho_\mathrm{xx}$, carrier density, and mobility show almost no temperature dependence in the measured range of 2$-$300 K, indicating Bi$_2$Rh$_2$O$_7$ as one of the rare examples of conducting pyrochlore oxides.

cond-mat.mtrl-sci↗

arXiv2023

Novel supercell compounds of layered Bi-Rh-O with $p$-type metallic conduction materialized as a thin film form

Layered oxides have been intensively studied due to their high degree of freedom in designing various electromagnetic properties and functionalities. While Bi-based layered supercell (LSC) compounds [Bi$_n$O$_{n+\delta}$]-[$M$O$_2$] ($M$ = Mn, Mn/Al, Mn/Fe, or Mn/Ni; $n=2, 3$) are a group of prospective candidates, all of the reported compounds are insulators. Here, we report on the synthesis of two novel metallic LSC compounds [Bi$_{n}$O$_{n+\delta}$]-[RhO$_2$] ($n=2, 3$) by pulsed laser deposition and subsequent annealing. With tuning the thickness of the sublattice from Bi$_2$O$_{2+\delta}$ to Bi$_3$O$_{3+\delta}$, a dimensionality-dependent electrical transport is revealed from a conventional metallic transport in $n=2$ to a localized transport in $n=3$. Our successful growth will be an important step for further exploring novel layered oxide compounds.

cond-mat.mtrl-sci↗

arXiv2022

The Second Catalog of Interplanetary Network Localizations of Konus Short Duration Gamma-Ray Bursts

We present the catalog of Interplanetary Network (IPN) localizations for 199 short-duration gamma-ray bursts (sGRBs) detected by the Konus-Wind (KW) experiment between 2011 January 1 and 2021 August 31, which extends the initial sample of IPN localized KW sGRBs (arXiv:1301.3740) to 495 events. We present the most comprehensive IPN localization data on these events, including probability sky maps in HEALPix format.

astro-ph.HE↗

arXiv2021

Molecular beam deposition of a new layered pnictide with distorted Sb square nets

While the family of layered pnictides $ABX_2$ ($A$ : rare or alkaline earth metals, $B$ : transition metals, $X$ : Sb/Bi) can host Dirac dispersions based on Sb/Bi square nets, nearly half of them has not been synthesized yet for possible combinations of the $A$ and $B$ cations. Here we report the fabrication of EuCdSb$_{\mathrm{2}}$ with the largest $B$-site ionic radius, which is stabilized for the first time in thin film form by molecular beam deposition. EuCdSb$_{\mathrm{2}}$ crystallizes in an orthorhombic $Pnma$ structure and exhibits antiferromagnetic ordering of the Eu magnetic moments at $T_\mathrm{N}=15$K. Our successful growth will be an important step for further exploring novel Dirac materials using film techniques.

cond-mat.mtrl-sci↗

arXiv2021

A software toolkit to simulate activation background for high energy detectors onboard satellites

A software toolkit for the simulation of activation background for high energy detectors onboard satellites is presented on behalf of the HERMES-SP collaboration. The framework employs direct Monte Carlo and analytical calculations allowing computations two orders of magnitude faster and more precise than a direct Monte Carlo simulation. The framework was developed in a way that the model of the satellite can be replaced easily. Therefore the framework can be used for different satellite missions. As an example, the proton induced activation background of the HERMES CubeSat is quantified.

astro-ph.IM↗

arXiv2019

Spectral analysis of Fermi-LAT gamma-ray bursts with known redshift and their potential use as cosmological standard candles

Long duration Gamma-Ray Bursts (LGRBs) may serve as standard candles to constrain cosmological parameters by probing the Hubble diagram well beyond the range of redshift currently accessible using type-Ia supernovae. The standardization of GRBs is based on phenomenological relations between two or more parameters found from spectral modeling, of which one is strongly dependent on the cosmological model. The Amati relation links the source-frame energy ${E_{\mathrm{i,p}}}$ at which the prompt gamma-ray spectral energy distribution $νF_ν$ peaks, and the isotropic-equivalent bolometric energy ${E_{\mathrm{iso}}}$ emitted during the prompt phase. We performed spectral analysis of 26 GRBs with known redshift that have been detected by the Fermi-Large Area Telescope (LAT) during its nine years of operations from July 2008 to September 2017, thus extending the computation of ${E_{\mathrm{iso}}}$ to the 100 MeV range. Multiple components are required to fit the spectra of a number of GRBs. We found that the Amati relation is satisfied by the 25 LGRBs, with best fit parameters similar to previous studies that used data from different satellite experiments, while the only short GRB with known redshift is an outlier. Using the Amati relation we extend the Hubble diagram to redshift 4.35 and constrain the Hubble constant and dark-energy density in the $Λ$CDM model, with Fermi-LAT GRBs alone and together with another sample of 94 GRBs and with the latest Supernovae type-Ia data. Our results are consistent with the currently acceptable ranges of those cosmological parameters within errors.

astro-ph.HE↗

arXiv2019

Estimation of the detected background by the future gamma-ray transient mission CAMELOT

This study presents a background estimation for the Cubesats Applied for MEasuring and LOcalising Transients (CAMELOT), which is a proposed fleet of nanosatellites for the all-sky monitoring and timing based localization of gamma-ray transients with precise localization capability at low Earth orbits. CAMELOT will allow to observe and precisely localize short gamma-ray bursts (GRBs) associated with kilonovae, long GRBs associated with core-collapse massive stars, magnetar outbursts, terrestrial gamma-ray flashes, and gamma-ray counterparts to gravitational wave sources. The fleet of at least nine 3U CubeSats is proposed to be equipped with large and thin CsI(Tl) scintillators read out by multi-pixel photon counters (MPPC). A careful study of the radiation environment in space is necessary to optimize the detector casing, estimate the duty cycle due to the crossing of the South Atlantic Anomaly and polar regions, and to minimize the effect of the radiation damage of MPPCs.

astro-ph.HE↗

arXiv2016

Investigation of Primordial Black Hole Bursts using Interplanetary Network Gamma-ray Bursts

The detection of a gamma-ray burst (GRB) in the solar neighborhood would have very important implications for GRB phenomenology. The leading theories for cosmological GRBs would not be able to explain such events. The final bursts of evaporating Primordial Black Holes (PBHs), however, would be a natural explanation for local GRBs. We present a novel technique that can constrain the distance to gamma-ray bursts using detections from widely separated, non-imaging spacecraft. This method can determine the actual distance to the burst if it is local. We applied this method to constrain distances to a sample of 36 short duration GRBs detected by the Interplanetary Network (IPN) that show observational properties that are expected from PBH evaporations. These bursts have minimum possible distances in the 10^13-10^18 cm (7-10^5 AU) range, consistent with the expected PBH energetics and with a possible origin in the solar neighborhood, although none of the bursts can be unambiguously demonstrated to be local. Assuming these bursts are real PBH events, we estimate lower limits on the PBH burst evaporation rate in the solar neighborhood.

astro-ph.HE↗

arXiv2015

Thermal Conductivity in the Frustrated Two-Leg Spin-Ladder System BiCu2PO6

We have measured temperature and magnetic-field dependences of the thermal conductivity of single crystals of the frustrated two-leg spin-ladder system BiCu2PO6 in magnetic fields up to 14 T. It has been found that the temperature dependence of the thermal conductivity along every principal crystallographic axis shows two peaks in zero field but that the magnitude of the thermal conductivity along the b-axis parallel to spin ladders, $κ$b, is significantly larger than those of the thermal conductivity along the a-axis, $κ$a, and along the c-axis, $κ$c, at high temperatures above 7 K. These results suggest that the thermal conductivity due to spins probably exists only in $κ$b. Furthermore, it has been found that both magnetic-field dependences of $κ$a and $κ$b at 3 K show kinks at ~ 7 T and ~ 10 T, where the spin state may change.

cond-mat.str-el↗

arXiv2015

Thermal Conductivity of the S = 1/2 Quasi-One-Dimensional Ferromagnetic Spin System CsCuCl3

We have measured the thermal conductivity along the c-axis, \k{appa}||c, parallel to ferromagnetic spin-chains of single crystals of the S = 1/2 quasi-one-dimensional spin system CsCuCl3 in magnetic fields up to 14 T, in order to investigate the thermal conductivity due to spins, \k{appa}spin, and the change of thermal conductivity corresponding to the change of the spin state. In the temperature dependence of \k{appa}||c, no contribution of \k{appa}spin has been observed, while a dip has been observed at the antiferromagnetic phase transition temperature, TN. Furthermore, it has been found that \k{appa}||c at a low temperature of 5.1 K below TN changes with increasing field perpendicular to the c-axis in good correspondence to the field-induced change of the spin state.

cond-mat.str-el↗

arXiv2015

Thermal Conductivity in the Triangular-Lattice Antiferromagnet Ba3CoSb2O9

We have measured the thermal conductivity in the ab-plane, $κ$ab, and along the c-axis, $κ$c, of single crystals of the S = 1/2 triangular-lattice antiferromagnet Ba3CoSb2O9 in zero field and magnetic fields. In zero field, it has been found that both $κ$ab and $κ$c show a similar broad peak around 40 K, suggesting that the thermal conductivity due to phonons is dominant in this compound and that the mean free path of phonons is suppressed so much by strong magnetic-fluctuations due to the magnetic frustration. It has also been found that both $κ$ab and $κ$c show a kink at the antiferromagnetic transition temperature TN. In magnetic fields parallel to the ab-plane up to 14 T, magnetic-field dependences of both $κ$ab and $κ$c at temperatures below and above TN have been found to be understood taking into account the phonon-magnon scattering in the so-called 120$°$ structure phase and the up-up-down (UUD) phase, while the minima of $κ$ab and $κ$c observed in the middle of the UUD phase have not been understood. This suggests the occurrence of some change of the magnetic state in the middle of the UUD phase.

cond-mat.str-el↗

arXiv2015

Multiwavelength Evidence for Quasi-periodic Modulation in the Gamma-ray Blazar PG 1553+113

We report for the first time a gamma-ray and multi-wavelength nearly-periodic oscillation in an active galactic nucleus. Using the Fermi Large Area Telescope (LAT) we have discovered an apparent quasi-periodicity in the gamma-ray flux (E >100 MeV) from the GeV/TeV BL Lac object PG 1553+113. The marginal significance of the 2.18 +/-0.08 year-period gamma-ray cycle is strengthened by correlated oscillations observed in radio and optical fluxes, through data collected in the OVRO, Tuorla, KAIT, and CSS monitoring programs and Swift UVOT. The optical cycle appearing in ~10 years of data has a similar period, while the 15 GHz oscillation is less regular than seen in the other bands. Further long-term multi-wavelength monitoring of this blazar may discriminate among the possible explanations for this quasi-periodicity.

astro-ph.HE↗

arXiv2015

The Third Catalog of Active Galactic Nuclei Detected by the Fermi Large Area Telescope

The third catalog of active galactic nuclei (AGNs) detected by the Fermi-LAT (3LAC) is presented. It is based on the third Fermi-LAT catalog (3FGL) of sources detected between 100 MeV and 300 GeV with a Test Statistic (TS) greater than 25, between 2008 August 4 and 2012 July 31. The 3LAC includes 1591 AGNs located at high Galactic latitudes (|b|>10°), a 71% increase over the second catalog based on 2 years of data. There are 28 duplicate associations, thus 1563 of the 2192 high-latitude gamma-ray sources of the 3FGL catalog are AGNs. Most of them (98%) are blazars. About half of the newly detected blazars are of unknown type, i.e., they lack spectroscopic information of sufficient quality to determine the strength of their emission lines. Based on their gamma-ray spectral properties, these sources are evenly split between flat-spectrum radio quasars (FSRQs) and BL~Lacs. The most abundant detected BL~Lacs are of the high-synchrotron-peaked (HSP) type. About 50% of the BL~Lacs have no measured redshifts. A few new rare outliers (HSP-FSRQs and high-luminosity HSP BL~Lacs) are reported. The general properties of the 3LAC sample confirm previous findings from earlier catalogs. The fraction of 3LAC blazars in the total population of blazars listed in BZCAT remains non-negligible even at the faint ends of the BZCAT-blazar radio, optical and X-ray flux distributions, which is a clue that even the faintest known blazars could eventually shine in gamma rays at LAT-detection levels. The energy-flux distributions of the different blazar populations are in good agreement with extrapolation from earlier catalogs.

astro-ph.HE↗

arXiv2015

A Missing-Link in the Supernova-GRB Connection: The Case of SN 2012ap

Gamma Ray Bursts (GRBs) are characterized by ultra-relativistic outflows, while supernovae are generally characterized by non-relativistic ejecta. GRB afterglows decelerate rapidly usually within days, because their low-mass ejecta rapidly sweep up a comparatively larger mass of circumstellar material. However supernovae, with heavy ejecta, can be in nearly free expansion for centuries. Supernovae were thought to have non-relativistic outflows except for few relativistic ones accompanied by GRBs. This clear division was blurred by SN 2009bb, the first supernova with a relativistic outflow without an observed GRB. Yet the ejecta from SN 2009bb was baryon loaded, and in nearly-free expansion for a year, unlike GRBs. We report the first supernova discovered without a GRB, but with rapidly decelerating mildly relativistic ejecta, SN 2012ap. We discovered a bright and rapidly evolving radio counterpart driven by the circumstellar interaction of the relativistic ejecta. However, we did not find any coincident GRB with an isotropic fluence of more than a sixth of the fluence from GRB 980425. This shows for the first time that central engines in type Ic supernovae, even without an observed GRB, can produce both relativistic and rapidly decelerating outflows like GRBs.

astro-ph.HE↗

arXiv2015

Observations of Gamma-ray Bursts with ASTRO-H and Fermi

ASTRO-H, the sixth Japanese X-ray observatory, which is scheduled to be launched by the end of Japanese fiscal year 2015 has a capability to observe the prompt emission from Gamma-ray Bursts (GRBs) utilizing BGO active shields for the soft gamma-ray detector (SGD). The effective area of the SGD shield detectors is very large and its data acquisition system is optimized for short transients such as short GRBs. Thus, we expect to perform more detailed time-resolved spectral analysis with a combination of ASTRO-H and Fermi LAT/GBM to investigate the gamma-ray emission mechanism of short GRBs. In addition, the environment of the GRB progenitor should be a remarkable objective from the point of view of the chemical evolution of high-z universe. If we can maneuver the spacecraft to the GRBs, we can perform a high-resolution spectroscopy of the X-ray afterglow of GRBs utilizing the onboard micro calorimeter and X-ray CCD camera.

astro-ph.HE↗

arXiv2015

Gamma-ray flaring activity from the gravitationally lensed blazar PKS 1830-211 observed by Fermi LAT

The Large Area Telescope (LAT) on board the Fermi Gamma-ray Space Telescope routinely detects the highly dust-absorbed, reddened, and MeV-peaked flat spectrum radio quasar PKS 1830-211 (z=2.507). Its apparent isotropic gamma-ray luminosity (E>100 MeV) averaged over $\sim$ 3 years of observations and peaking on 2010 October 14/15 at 2.9 X 10^{50} erg s^{-1}, makes it among the brightest high-redshift Fermi blazars. No published model with a single lens can account for all of the observed characteristics of this complex system. Based on radio observations, one expects time delayed variability to follow about 25 days after a primary flare, with flux about a factor 1.5 less. Two large gamma-ray flares of PKS 1830-211 have been detected by the LAT in the considered period and no substantial evidence for such a delayed activity was found. This allows us to place a lower limit of about 6 on the gamma rays flux ratio between the two lensed images. Swift XRT observations from a dedicated Target of Opportunity program indicate a hard spectrum and with no significant correlation of X-ray flux with the gamma-ray variability. The spectral energy distribution can be modeled with inverse Compton scattering of thermal photons from the dusty torus. The implications of the LAT data in terms of variability, the lack of evident delayed flare events, and different radio and gamma-ray flux ratios are discussed. Microlensing effects, absorption, size and location of the emitting regions, the complex mass distribution of the system, an energy-dependent inner structure of the source, and flux suppression by the lens galaxy for one image path may be considered as hypotheses for understanding our results.

astro-ph.HE↗

arXiv2014

ASTRO-H White Paper - Accreting Pulsars, Magnetars, and Related Sources

As the endpoints of massive star evolution, neutron stars are enigmatic celestial objects characterized by extremely dense and exotic nuclear matter, magnetospheres with positrons (antimatter), rapid rotation and ultra-strong magnetic fields. Such an extreme environment has provided an accessible astrophysical laboratory to study physics under conditions unattainable on Earth and to tackle a range of fundamental questions related to: the aftermath of stellar evolution and the powerful explosions of massive stars, the equation of state and physics of some of the most exotic and magnetic stars in the Universe, the workings of the most powerful particle accelerators in our Galaxy and beyond, and the sources of gravitational waves that are yet to be detected. Recent observations revealed a great diversity of neutron stars, including ultra-strongly magnetized pulsars, referred to as "magnetars", and unusual types of accreting X-ray pulsars. In this white paper, we highlight the prospects of the upcoming X-ray mission, ASTRO-H, in studying these highly magnetized neutron stars.

astro-ph.HE↗

arXiv2014

ASTRO-H White Paper - Chemical Evolution in High-z Universe

In this paper, we demonstrate ASTRO-H's capability to measure the chemical evolution in the high-z (z <~ 3) universe by observing X-ray afterglows of gamma-ray bursts (GRBs) and distant Blazars. Utilizing these sources as background light sources, the excellent energy resolution of ASTRO-H/SXS allows us to detect emission and absorption features from heavy elements in the circumstellar material in the host galaxies, from the intergalactic medium (IGM) and in the ejecta of GRB explosions. In particular, we can constrain the existence of the warm-hot intergalactic material (WHIM), thought to contain most of the baryons at redshift of z < ~3, with a typical exposure of one day for a follow-up observation of a GRB afterglow or 300 ks exposure for several distant Blazars. In addition to the chemical evolution study, the combination of the SGD, HXI, SXI and SXS will measure, for the first time, the temporal behavior of the spectral continuum of GRB afterglows and Blazars over a broad energy range and short time scales allowing detailed modeling of jets. The ability to obtain these data from GRB afterglows will depend critically on the availability of GRB triggers and the capability of ASTRO-H to respond rapidly to targets of opportunity. At the present time it seems as if Swift will still be functioning normally during the first two years of ASTRO-H operations providing the needed triggering capability.

astro-ph.HE↗