تقرير
Evidence for X-ray Emission in Excess to the Jet Afterglow Decay 3.5 yrs After the Binary Neutron Star Merger GW 170817: A New Emission Component
| العنوان: | Evidence for X-ray Emission in Excess to the Jet Afterglow Decay 3.5 yrs After the Binary Neutron Star Merger GW 170817: A New Emission Component |
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| المؤلفون: | Hajela, A., Margutti, R., Bright, J. S., Alexander, K. D., Metzger, B. D., Nedora, V., Kathirgamaraju, A., Margalit, B., Radice, D., Guidorzi, C., Berger, E., MacFadyen, A., Giannios, D., Chornock, R., Heywood, I., Sironi, L., Gottlieb, O., Coppejans, D., Laskar, T., Cendes, Y., Duran, R. Barniol, Eftekhari, T., Fong, W., McDowell, A., Nicholl, M., Xie, X., Zrake, J., Bernuzzi, S., Broekgaarden, F. S., Kilpatrick, C. D., Terreran, G., Villar, V. A., Blanchard, P. K., Gomez, S., Hosseinzadeh, G., Matthews, D. J., Rastinejad, J. C. |
| سنة النشر: | 2021 |
| المجموعة: | Astrophysics |
| مصطلحات موضوعية: | Astrophysics - High Energy Astrophysical Phenomena |
| الوصف: | For the first $\sim3$ years after the binary neutron star merger event GW 170817 the radio and X-ray radiation has been dominated by emission from a structured relativistic off-axis jet propagating into a low-density medium with n $< 0.01\,\rm{cm^{-3}}$. We report on observational evidence for an excess of X-ray emission at $\delta t>900$ days after the merger. With $L_x\approx5\times 10^{38}\,\rm{erg\,s^{-1}}$ at 1234 days, the recently detected X-ray emission represents a $\ge 3.2\,\sigma$ (Gaussian equivalent) deviation from the universal post jet-break model that best fits the multi-wavelength afterglow at earlier times. In the context of JetFit afterglow models, current data represent a departure with statistical significance $\ge 3.1\,\sigma$, depending on the fireball collimation, with the most realistic models showing excesses at the level of $\ge 3.7\,\sigma$. A lack of detectable 3 GHz radio emission suggests a harder broad-band spectrum than the jet afterglow. These properties are consistent with the emergence of a new emission component such as synchrotron radiation from a mildly relativistic shock generated by the expanding merger ejecta, i.e. a kilonova afterglow. In this context, we present a set of ab-initio numerical-relativity BNS merger simulations that show that an X-ray excess supports the presence of a high-velocity tail in the merger ejecta, and argues against the prompt collapse of the merger remnant into a black hole. Radiation from accretion processes on the compact-object remnant represents a viable alternative. Neither a kilonova afterglow nor accretion-powered emission have been observed before, as detections of BNS mergers at this phase of evolution are unprecedented. Comment: 30 pages, 13 figures, Accepted for publication in ApJL |
| نوع الوثيقة: | Working Paper |
| DOI: | 10.3847/2041-8213/ac504a |
| URL الوصول: | http://arxiv.org/abs/2104.02070 |
| رقم الأكسشن: | edsarx.2104.02070 |
| قاعدة البيانات: | arXiv |
| DOI: | 10.3847/2041-8213/ac504a |
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