تقرير
The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/VIRGO GW170817. III. Optical and UV Spectra of a Blue Kilonova From Fast Polar Ejecta
| العنوان: | The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/VIRGO GW170817. III. Optical and UV Spectra of a Blue Kilonova From Fast Polar Ejecta |
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| المؤلفون: | Nicholl, M., Berger, E., Kasen, D., Metzger, B. D., Elias, J., Briceno, C., Alexander, K. D., Blanchard, P. K., Chornock, R., Cowperthwaite, P. S., Eftekhari, T., Fong, W., Margutti, R., Villar, V. A., Williams, P. K. G., Brown, W., Annis, J., Bahramian, A., Brout, D., Brown, D. A., Chen, H. -Y., Clemens, J. C., Dennihy, E., Dunlap, B., Holz, D. E., Marchesini, E., Massaro, F., Moskowitz, N., Pelisoli, I., Rest, A., Ricci, F., Sako, M., Soares-Santos, M., Strader, J. |
| سنة النشر: | 2017 |
| المجموعة: | Astrophysics |
| مصطلحات موضوعية: | Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Cosmology and Nongalactic Astrophysics, Astrophysics - Solar and Stellar Astrophysics |
| الوصف: | We present optical and ultraviolet spectra of the first electromagnetic counterpart to a gravitational wave (GW) source, the binary neutron star merger GW170817. Spectra were obtained nightly between 1.5 and 9.5 days post-merger, using the SOAR and Magellan telescopes; the UV spectrum was obtained with the \textit{Hubble Space Telescope} at 5.5 days. Our data reveal a rapidly-fading blue component ($T\approx5500$ K at 1.5 days) that quickly reddens; spectra later than $\gtrsim 4.5$ days peak beyond the optical regime. The spectra are mostly featureless, although we identify a possible weak emission line at $\sim 7900$ \AA\ at $t\lesssim 4.5$ days. The colours, rapid evolution and featureless spectrum are consistent with a "blue" kilonova from polar ejecta comprised mainly of light $r$-process nuclei with atomic mass number $A\lesssim 140$. This indicates a sight-line within $\theta_{\rm obs}\lesssim 45^{\circ}$ of the orbital axis. Comparison to models suggests $\sim0.03$ M$_\odot$ of blue ejecta, with a velocity of $\sim 0.3c$. The required lanthanide fraction is $\sim 10^{-4}$, but this drops to $<10^{-5}$ in the outermost ejecta. The large velocities point to a dynamical origin, rather than a disk wind, for this blue component, suggesting that both binary constituents are neutron stars (as opposed to a binary consisting of a neutron star and a black hole). For dynamical ejecta, the high mass favors a small neutron star radius of $\lesssim 12$ km. This mass also supports the idea that neutron star mergers are a major contributor to $r$-process nucleosynthesis. Comment: ApJL, in press (GW170817, LVC) |
| نوع الوثيقة: | Working Paper |
| DOI: | 10.3847/2041-8213/aa9029 |
| URL الوصول: | http://arxiv.org/abs/1710.05456 |
| رقم الأكسشن: | edsarx.1710.05456 |
| قاعدة البيانات: | arXiv |
| DOI: | 10.3847/2041-8213/aa9029 |
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