On the Blackbody Spectrum of Kilonovae

On the Blackbody Spectrum of Kilonovae

Blog Article

The early spectra of the kilonova AT2017gfo have a remarkably smooth blackbody continuum, which reveals information on the thermal properties and radioactive heating within the ejecta.However, the widespread use of a single-temperature blackbody to fit kilonova Fridge Handle Mount data is theoretically invalid, because (1) the significant travel-time delays for a rapidly cooling surface result in a broad distribution of temperatures and (2) the relativistic Doppler correction varies across different surface elements.Thus, the observed spectrum should be a modified blackbody with a range of temperatures over the surface.

In this paper we quantify the impact of these effects and illustrate the typical wavelength-dependent spectral corrections.We apply the multitemperature blackbody framework to the first-epoch X-shooter AT2017gfo spectrum, to deconvolve the underlying physical temperature at the photosphere from the relativistic Doppler shift.We show that the cooling and Doppler Air Hoses effects individually result in a variation of temperatures over the photosphere of up to 30%, but in combination these effects nearly cancel and produce the single-temperature blackbody observed.

Finally, we show that fitting the UV, optical, or near-infrared separately yields blackbody temperatures consistent at the percent level, which puts stringent limits on any proposed modification of the spectral continuum.