Non-thermal emission from mildly relativistic dynamical ejecta of neutron star mergers: spectrum and sky image
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| Format: | Preprint |
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2024
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| _version_ | 1866910458500349952 |
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| author | Sadeh, Gilad Linder, Noya Waxman, Eli |
| author_facet | Sadeh, Gilad Linder, Noya Waxman, Eli |
| contents | Binary neutron star mergers are expected to produce fast dynamical ejecta, with mildly relativistic velocities extending to $β=v/c>0.6$. In a preceding paper, we derived an analytic description of the time-dependent radio to X-ray synchrotron flux produced by collisionless shocks driven by such fast ejecta into the interstellar medium, for spherical ejecta with broken power-law mass (or energy) distributions, $M(>γβ)\propto(γβ)^{-s}$ with $s=s_\text{KN}$ at $γβ<γ_0β_0$ and $s=s_\text{ft}$ at $γβ>γ_0β_0$ (where $γ$ is the Lorentz factor). Here, we extend our analysis and provide analytic expressions for the self-absorption frequency, the cooling frequency, and the observed angular size of the emitting region (which appears as a ring in the sky). For parameter values characteristic of merger calculation results -- a "shallow" mass distribution, $1<s_\text{KN}<3$, for the bulk of the ejecta (at $γβ\approx0.2$), and a steep, $s_\text{ft}>5$, "fast tail" mass distribution -- the analytic results reproduce well (to tens of percent accuracy) the results of detailed numeric calculations, a significant improvement over earlier order-of-magnitude estimates (based on extrapolations of results valid for $γβ\ll1$). |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2403_07047 |
| institution | arXiv |
| publishDate | 2024 |
| record_format | arxiv |
| spellingShingle | Non-thermal emission from mildly relativistic dynamical ejecta of neutron star mergers: spectrum and sky image Sadeh, Gilad Linder, Noya Waxman, Eli High Energy Astrophysical Phenomena Binary neutron star mergers are expected to produce fast dynamical ejecta, with mildly relativistic velocities extending to $β=v/c>0.6$. In a preceding paper, we derived an analytic description of the time-dependent radio to X-ray synchrotron flux produced by collisionless shocks driven by such fast ejecta into the interstellar medium, for spherical ejecta with broken power-law mass (or energy) distributions, $M(>γβ)\propto(γβ)^{-s}$ with $s=s_\text{KN}$ at $γβ<γ_0β_0$ and $s=s_\text{ft}$ at $γβ>γ_0β_0$ (where $γ$ is the Lorentz factor). Here, we extend our analysis and provide analytic expressions for the self-absorption frequency, the cooling frequency, and the observed angular size of the emitting region (which appears as a ring in the sky). For parameter values characteristic of merger calculation results -- a "shallow" mass distribution, $1<s_\text{KN}<3$, for the bulk of the ejecta (at $γβ\approx0.2$), and a steep, $s_\text{ft}>5$, "fast tail" mass distribution -- the analytic results reproduce well (to tens of percent accuracy) the results of detailed numeric calculations, a significant improvement over earlier order-of-magnitude estimates (based on extrapolations of results valid for $γβ\ll1$). |
| title | Non-thermal emission from mildly relativistic dynamical ejecta of neutron star mergers: spectrum and sky image |
| topic | High Energy Astrophysical Phenomena |
| url | https://arxiv.org/abs/2403.07047 |