A Hubble Space Telescope Search for r-Process Nucleosynthesis in Gamma-Ray Burst Supernovae
Covino, S.; Melandri, A.; Pian, E.; Fruchter, A. S.; Hartmann, D. H.; Milvang-Jensen, B.; Fynbo, J. P. U.; Rossi, A.; Izzo, L.; Levan, A. J.; Fong, W.; Tanvir, N. R.; Jakobsson, P.; Kilpatrick, C. D.; Heintz, K. E.; Metzger, B. D.; Lamb, G. P.; Bhirombhakdi, K.; Malesani, D. B.; Pugliese, G.; Rastinejad, J. C.; Stratta, G.; Kangas, T.; Singh, P.; Anand, S.; Halevi, G.; Siegel, D. M.
United States, Netherlands, United Kingdom, Italy, Denmark, Iceland, Finland, Germany, Canada
Abstract
The existence of a secondary (in addition to compact object mergers) source of heavy element (r-process) nucleosynthesis, the core-collapse of rapidly rotating and highly magnetized massive stars, has been suggested by both simulations and indirect observational evidence. Here, we probe a predicted signature of r-process enrichment, a late-time (≳40 days post-burst) distinct red color, in observations of gamma-ray burst supernovae (GRB-SNe), which are linked to these massive star progenitors. We present optical to near-IR color measurements of four GRB-SNe at z ≲ 0.4, extending out to >500 days post-burst, obtained with the Hubble Space Telescope and large-aperture ground-based telescopes. Comparison of our observations to models indicates that GRBs 030329, 100316D, and 130427A are consistent with both no enrichment and producing 0.01–0.15 M ⊙ of r-process material if there is a low amount of mixing between the inner r-process ejecta and outer supernova (SN) layers. GRB 190829A is not consistent with any models with r-process enrichment ≥0.01 M ⊙. Taken together the sample of GRB-SNe indicates color diversity at late times. Our derived yields from GRB-SNe may be underestimated due to r-process material hidden in the SN ejecta (potentially due to low mixing fractions) or the limits of current models in measuring r-process mass. We conclude with recommendations for future search strategies to observe and probe the full distribution of r-process produced by GRB-SNe.