Inferring Kilonova Ejecta Photospheric Properties from Early Blackbody Spectra
We present simple analytic corrections to the standard blackbody fitting used for early kilonova emission. We consider a spherical, relativistically expanding shell that radiates thermally at a single temperature in its own rest frame. Due to relativistic effects, including Doppler boosting, time de...
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IOP Publishing
2025-01-01
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| Series: | The Astrophysical Journal |
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| Online Access: | https://doi.org/10.3847/1538-4357/adecee |
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| author | Gilad Sadeh |
| author_facet | Gilad Sadeh |
| author_sort | Gilad Sadeh |
| collection | DOAJ |
| description | We present simple analytic corrections to the standard blackbody fitting used for early kilonova emission. We consider a spherical, relativistically expanding shell that radiates thermally at a single temperature in its own rest frame. Due to relativistic effects, including Doppler boosting, time delay, and temperature evolution, the observed temperature is smeared across different polar angles by approximately ∼10%. While the observed spectrum remains roughly consistent with a single-temperature blackbody, neglecting relativistic effects leads to significant systematic inaccuracies: the inferred photospheric velocity and temperature are overestimated by up to ∼50% for mildly relativistic velocities. By applying our analytic corrections, these deviations are reduced to within 10%, even in cases where the photosphere is receding and cooling is considered. Applying our corrections to observed kilonovae (AT2017gfo and the thermal component of GRB 211211A) reveals that standard blackbody fitting overestimated the inferred velocities and temperatures by 10%–40%; such deviations can alter the inferred formation of heavy elements. |
| format | Article |
| id | doaj-art-98e534ab55dd4edca54a7c8c5ffeb6f3 |
| institution | Kabale University |
| issn | 1538-4357 |
| language | English |
| publishDate | 2025-01-01 |
| publisher | IOP Publishing |
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| series | The Astrophysical Journal |
| spelling | doaj-art-98e534ab55dd4edca54a7c8c5ffeb6f32025-08-20T03:27:29ZengIOP PublishingThe Astrophysical Journal1538-43572025-01-01988113010.3847/1538-4357/adeceeInferring Kilonova Ejecta Photospheric Properties from Early Blackbody SpectraGilad Sadeh0https://orcid.org/0009-0003-0141-6171Dept. of Particle Phys. & Astrophys., Weizmann Institute of Science , Rehovot 76100, IsraelWe present simple analytic corrections to the standard blackbody fitting used for early kilonova emission. We consider a spherical, relativistically expanding shell that radiates thermally at a single temperature in its own rest frame. Due to relativistic effects, including Doppler boosting, time delay, and temperature evolution, the observed temperature is smeared across different polar angles by approximately ∼10%. While the observed spectrum remains roughly consistent with a single-temperature blackbody, neglecting relativistic effects leads to significant systematic inaccuracies: the inferred photospheric velocity and temperature are overestimated by up to ∼50% for mildly relativistic velocities. By applying our analytic corrections, these deviations are reduced to within 10%, even in cases where the photosphere is receding and cooling is considered. Applying our corrections to observed kilonovae (AT2017gfo and the thermal component of GRB 211211A) reveals that standard blackbody fitting overestimated the inferred velocities and temperatures by 10%–40%; such deviations can alter the inferred formation of heavy elements.https://doi.org/10.3847/1538-4357/adeceeUltraviolet transient sourcesGravitational wave sourcesRelativistic fluid dynamicsNeutron stars |
| spellingShingle | Gilad Sadeh Inferring Kilonova Ejecta Photospheric Properties from Early Blackbody Spectra The Astrophysical Journal Ultraviolet transient sources Gravitational wave sources Relativistic fluid dynamics Neutron stars |
| title | Inferring Kilonova Ejecta Photospheric Properties from Early Blackbody Spectra |
| title_full | Inferring Kilonova Ejecta Photospheric Properties from Early Blackbody Spectra |
| title_fullStr | Inferring Kilonova Ejecta Photospheric Properties from Early Blackbody Spectra |
| title_full_unstemmed | Inferring Kilonova Ejecta Photospheric Properties from Early Blackbody Spectra |
| title_short | Inferring Kilonova Ejecta Photospheric Properties from Early Blackbody Spectra |
| title_sort | inferring kilonova ejecta photospheric properties from early blackbody spectra |
| topic | Ultraviolet transient sources Gravitational wave sources Relativistic fluid dynamics Neutron stars |
| url | https://doi.org/10.3847/1538-4357/adecee |
| work_keys_str_mv | AT giladsadeh inferringkilonovaejectaphotosphericpropertiesfromearlyblackbodyspectra |