Kyoto University · Physics and Astronomy
Professor Tomohiko Oka's research lab specializes in high-energy astrophysics, focusing on multi-messenger astronomy involving gamma rays, neutrinos, and cosmic rays. The lab investigates high-energy emission mechanisms in transient and persistent sources such as blazars, pulsars, and supernova remnants, with particular emphasis on diffusive shock acceleration and particle acceleration in extreme environments. Utilizing data from major observatories including Fermi-LAT, MAGIC, H.E.S.S., IceCube, and X-ray telescopes, the lab explores the connections between high-energy radiation and underlying astrophysical processes. Their work also includes detailed spectral and temporal analyses to constrain source distances, particle populations, and extragalactic background light effects.
Figures are computed from collected data and may differ slightly.
Abstract The blazar TXS 0506+056 got into the spotlight of the astrophysical community in 2017 September, when a high-energy neutrino detected by IceCube (IceCube-170922A) was associated at the 3 σ level with a γ -ray flare from this source. This multi-messenger photon-neutrino association remains, as per today, the most significant association ever observed. TXS 0506+056 was a poorly studied object before the IceCube-170922A event. To better characterize its broadband emission, we organized a m
Abstract The results of gamma-ray observations of the binary system HESS J0632 + 057 collected during 450 hr over 15 yr, between 2004 and 2019, are presented. Data taken with the atmospheric Cherenkov telescopes H.E.S.S., MAGIC, and VERITAS at energies above 350 GeV were used together with observations at X-ray energies obtained with Swift-XRT, Chandra, XMM-Newton, NuSTAR, and Suzaku. Some of these observations were accompanied by measurements of the H α emission line. A significant detection of
Abstract We analyze the GeV gamma-ray emission data from the vicinity of the supernova remnant (SNR) HB9 (G160.9+2.6) from the Fermi-LAT 12 yr observations to quantify the evolution of diffusive shock acceleration (DSA) in the SNR. In the vicinity of HB9, there are molecular clouds whose locations do not coincide with the SNR shell in the line of sight. We detect significant gamma-ray emissions above 1 GeV spatially coinciding with the two prominent cloud regions, as well as emission from the SN
Abstract We report on a long-lasting, elevated gamma-ray flux state from VER J0521+211 observed by VERITAS, MAGIC, and Fermi-LAT in 2013 and 2014. The peak integral flux above 200 GeV measured with the nightly binned light curve is (8.8 ± 0.4) × 10 −7 photons m −2 s −1 , or ∼37% of the Crab Nebula flux. Multiwavelength observations from X-ray, UV, and optical instruments are also presented. A moderate correlation between the X-ray and TeV gamma-ray fluxes was observed, and the X-ray spectrum app
Abstract PSR J0218+4232 is one of the most energetic millisecond pulsars known and has long been considered as one of the best candidates for very high-energy (VHE; >100 GeV) γ -ray emission. Using 11.5 yr of Fermi Large Area Telescope (LAT) data between 100 MeV and 870 GeV, and ∼90 hr of Major Atmospheric Gamma Imaging Cherenkov (MAGIC) observations in the 20 GeV to 20 TeV range, we searched for the highest energy γ -ray emission from PSR J0218+4232. Based on the analysis of the LAT data, we
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