arXiv subjects

K. Ishio

Publications and source records attributed to K. Ishio.

75 records · Page 5Linked to original sources

arXiv2017

Observation of the Black Widow B1957+20 millisecond pulsar binary system with the MAGIC telescopes

B1957+20 is a millisecond pulsar located in a black widow type compact binary system with a low mass stellar companion. The interaction of the pulsar wind with the companion star wind and/or the interstellar plasma is expected to create plausible conditions for acceleration of electrons to TeV energies and subsequent production of very high energy γ rays in the inverse Compton process. We performed extensive observations with the MAGIC telescopes of B1957+20. We interpret results in the framework of a few different models, namely emission from the vicinity of the millisecond pulsar, the interaction of the pulsar and stellar companion wind region, or bow shock nebula. No significant steady very high energy γ-ray emission was found. We derived a 95% confidence level upper limit of 3.0 x 10 -12 cm -2 s -1 on the average γ-ray emission from the binary system above 200 GeV. The upper limits obtained with MAGIC constrain, for the first time, different models of the high-energy emission in B1957+20. In particular, in the inner mixed wind nebula model with mono-energetic injection of electrons, the acceleration efficiency of electrons is constrained to be below ~(2-10)% of the pulsar spin down power. For the pulsar emission, the obtained upper limits for each emission peak are well above the exponential cut-off fits to the Fermi-LAT data, extrapolated to energies above 50 GeV. The MAGIC upper limits can rule out a simple power-law tail extension through the sub-TeV energy range for the main peak seen at radio frequencies.

astro-ph.HE↗

arXiv2017

First Multi-wavelength Campaign on the Gamma-ray-loud Active Galaxy IC 310

The extragalactic VHE gamma-ray sky is rich in blazars. These are jetted active galactic nuclei viewed at a small angle to the line-of-sight. Only a handful of objects viewed at a larger angle are known so far to emit above 100 GeV. Multi-wavelength studies of such objects up to the highest energies provide new insights into the particle and radiation processes of active galactic nuclei. We report the results from the first multi-wavelength campaign observing the TeV detected nucleus of the active galaxy IC 310, whose jet is observed at a moderate viewing angle of 10 deg - 20 deg. The multi-instrument campaign was conducted between 2012 Nov. and 2013 Jan., and involved observations with MAGIC, Fermi, INTEGRAL, Swift, OVRO, MOJAVE and EVN. These observations were complemented with archival data from the AllWISE and 2MASS catalogs. A one-zone synchrotron self-Compton model was applied to describe the broad-band spectral energy distribution. IC 310 showed an extraordinary TeV flare at the beginning of the campaign, followed by a low, but still detectable TeV flux. Compared to previous measurements, the spectral shape was found to be steeper during the low emission state. Simultaneous observations in the soft X-ray band showed an enhanced energy flux state and a harder-when-brighter spectral shape behaviour. No strong correlated flux variability was found in other frequency regimes. The broad-band spectral energy distribution obtained from these observations supports the hypothesis of a double-hump structure. The harder-when-brighter trend in the X-ray and VHE emission is consistent with the behaviour expected from a synchrotron self-Compton scenario. The contemporaneous broad-band spectral energy distribution is well described with a one-zone synchrotron self-Compton model using parameters that are comparable to those found for other gamma-ray-emitting misaligned blazars.

astro-ph.HE↗

arXiv2017

Multiwavelength observations of a VHE gamma-ray flare from PKS 1510-089 in 2015

Context. PKS 1510-089 is one of only a few flat spectrum radio quasars detected in the VHE (very-high-energy, > 100 GeV) gamma-ray band. Aims. We study the broadband spectral and temporal properties of the PKS 1510-089 emission during a high gamma-ray state. Methods. We performed VHE gamma-ray observations of PKS 1510-089 with the MAGIC telescopes during a long high gamma-ray state in May 2015. In order to perform broadband modelling of the source, we have also gathered contemporaneous multiwavelength data in radio, IR, optical photometry and polarization, UV, X-ray and GeV gamma-ray ranges. We construct a broadband spectral energy distribution (SED) in two periods, selected according to VHE gamma-ray state. Results. PKS 1510-089 has been detected by MAGIC during a few day-long observations performed in the middle of a long, high optical and gamma-ray state, showing for the first time a significant VHE gamma-ray variability. Similarly to the optical and gamma-ray high state of the source detected in 2012, it was accompanied by a rotation of the optical polarization angle and the emission of a new jet component observed in radio. However, due to large uncertainty on the knot separation time, the association with the VHE gamma-ray emission cannot be firmly established. The spectral shape in the VHE band during the flare is similar to the ones obtained during previous measurements of the source. The observed flux variability sets for the first time constraints on the size of the region from which VHE gamma rays are emitted. We model the broadband SED in the framework of the external Compton scenario and discuss the possible emission site in view of multiwavelength data and alternative emission models.

astro-ph.HE↗