Detectability of compact binary merger macronovae

Abstract

We study the optical and near-infrared luminosities and detectability of radioactively powered electromagnetic transients ('macronovae') occuring in the aftermath of binary neutron star and neutron star black hole mergers. We explore the transients that result from the dynamic ejecta and those from different types of wind outflows. Based on full nuclear network simulations we calculate the resulting light curves in different wavelength bands. We scrutinize the robustness of the results by comparing a) two different nuclear reaction networks and b) two macronova models. We explore in particular how sensitive the results are to the production of α-decaying trans-lead nuclei. We compare two frequently used mass models: the Finite-Range Droplet Model (FRDM) and the nuclear mass model of Duflo and Zuker (DZ31). We find that the abundance of α-decaying trans-lead nuclei has a significant impact on the observability of the resulting macronovae. For example, the DZ31 model yields considerably larger abundances resulting in larger heating rates and thermalization efficiencies and therefore predicts substantially brighter macronova transients. We find that the dynamic ejecta from NSNS models can reach peak K-band magnitudes in excess of −15 while those from NSBH cases can reach beyond −16. Similar values can be reached by some of our wind models. Several of our models (both wind and dynamic ejecta) yield properties that are similar to the transient that was observed in the aftermath of the short GRB 130603B. We further explore the expected macronova detection frequencies for current and future instruments such as VISTA, ZTF and LSST.

Toward Rapid Transient Identification and Characterization of Kilonovae

“…Rosswog et al (2017) use semi-analytical models based on nuclear network simulations studying in detail the effect of the nuclear heating rate and ejecta electron fraction. The work of Rosswog et al (2017) shows in detail how lightcurve predictions change significantly for different nuclear physics parameters, e.g., the usage of different mass models.…”

“…Rosswog et al (2017) employ both time dependent and constant efficiencies and use a more complex density profile. The model picked from Rosswog et al (2017) shows a smaller bolometric luminosity than other models, notice, however, that as shown in Rosswog et al (2017) the usage of different mass models effects the luminosity by about ≈ 600%, i.e., all presented models come with large uncertainties and crucially depent on nuclear physics assumptions.…”

“…Rosswog et al (2017) employ both time dependent and constant efficiencies and use a more complex density profile. The model picked from Rosswog et al (2017) shows a smaller bolometric luminosity than other models, notice, however, that as shown in Rosswog et al (2017) the usage of different mass models effects the luminosity by about ≈ 600%, i.e., all presented models come with large uncertainties and crucially depent on nuclear physics assumptions. The model of Metzger et al (2015) describes the blue transient arising from a small fraction of the ejected mass which expands sufficiently rapidly such that the neutrons are not captured and instead β-decay, giving rise to a clear peak in the bolometric luminosity visible around the time of merger.…”

“…The model of Barnes et al (2016) assumes spherical ejecta with ρ ∝ r −1 for the density profile and the time-(mass)-dependent thermalization efficiency is taken into account. The model of Rosswog et al (2017) also assumes spherical ejecta with an homogeneously expanding density profile and time-(mass)-dependent thermalization efficiency with the FRDM model.…”

“…The yellow curve is similar to the blue curve but we employed a constant thermalization efficiency ( th = 1) and multiplied afterwards by the time-(mass)-dependent thermalization efficiency given in Barnes et al (2016). The red curve denotes the bolometric lightcurve employing Mej = 0.0079 and vej = 0.12, and the same density profile as in Rosswog et al (2017). stant gray opacity with 10 cm 2 g −1 , and the heating rate that is employed in Kawaguchi et al (2016) and Dietrich & Ujevic (2017).…”