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1
The X-ray counterpart to the gravitational-wave event GW170817

Troja, E.,Piro, L.,van Eerten, H.,Wollaeger, R. T.,Im, M.,Fox, O. D.,Butler, N. R.,Cenko, S. B.,Sakamoto, T.,Fryer, C. L.,Ricci, R.,Lien, A.,Ryan Jr, R. E.,Korobkin, O.,Lee, S.-K.,Burgess, J. M.,Lee, Nature Publishing Group 2017 Nature Vol. No.
- 원문보기
A long-standing paradigm in astrophysics is that collisions—or mergers—of two neutron stars form highly relativistic and collimated outflows (jets) that power γ-ray bursts of short (less than two seconds) duration. The observational support for this model, however, is only indirect. A hitherto outstanding prediction is that gravitational-wave events from such mergers should be associated with γ-ray bursts, and that a majority of these bursts should be seen off-axis, that is, they should point away from Earth. Here we report the discovery observations of the X-ray counterpart associated with the gravitational-wave event GW170817. Although the electromagnetic counterpart at optical and infrared frequencies is dominated by the radioactive glow (known as a ‘kilonova’) from freshly synthesized rapid neutron capture (r-process) material in the merger ejecta, observations at X-ray and, later, radio frequencies are consistent with a short γ-ray burst viewed off-axis. Our detection of X-ray emission at a location coincident with the kilonova transient provides the missing observational link between short γ-ray bursts and gravitational waves from neutron-star mergers, and gives independent confirmation of the collimated nature of the γ-ray-burst emission.
2
The Spectral Sharpness Angle of Gamma-ray Bursts

Hoi-Fung Yu,Hendrik J. van Eerten,Jochen Greiner,Re’em Sari,P. Narayana Bhat,Andreas von Kienlin,William S. Paciesas,Robert D. Preece 한국우주과학회 2016 Journal of Astronomy and Space Sciences Vol.33 No.2
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  ScienceON
  
  코리아스칼라
We explain the results of Yu et al. (2015b) of the novel sharpness angle measurement to a large number of spectra obtained from the Fermi gamma-ray burst monitor. The sharpness angle is compared to the values obtained from various representative emission models: blackbody, single-electron synchrotron, synchrotron emission from a Maxwellian or power-law electron distribution. It is found that more than 91% of the high temporally and spectrally resolved spectra are inconsistent with any kind of optically thin synchrotron emission model alone. It is also found that the limiting case, a single temperature Maxwellian synchrotron function, can only contribute up to 58+23 -18% of the peak flux. These results show that even the sharpest but non-realistic case, the single-electron synchrotron function, cannot explain a large fraction of the observed spectra. Since any combination of physically possible synchrotron spectra added together will always further broaden the spectrum, emission mechanisms other than optically thin synchrotron radiation are likely required in a full explanation of the spectral peaks or breaks of the GRB prompt emission phase.