Highly luminous supernovae associated with gamma-ray bursts: II. the luminous blue bump in the afterglow of GRB 140506A

Kann, D.A. and Rossi, A. and Oates, S.R. and Klose, S. and Blazek, M. and Agüí Fernández, J.F. and De Ugarte Postigo, A. and Thöne, C.C. and Schulze, S. (2024) Highly luminous supernovae associated with gamma-ray bursts: II. the luminous blue bump in the afterglow of GRB 140506A. Astronomy and Astrophysics, 684: A164. ISSN 0004-6361

Abstract

Context. The supernovae (SNe) associated with gamma-ray bursts (GRBs) are generally seen as a homogeneous population, but at least one exception exists: The highly luminous SN 2011kl associated with the ultra-long GRB 111209A. Such outliers may also exist for more typical GRBs. Aims. Within the context of a systematic analysis of photometric signatures of GRB-Associated SNe, we found an anomalous bump in the late-Time transient following GRB 140506A at redshift z = 0.889. We hereby aim to show this bump is significantly more luminous and blue than usual SNe following GRBs. Methods. We compiled all available data from the literature and added a full analysis of the Swift/UVOT data, which allowed us to trace the light curve from the first minutes all the way to the host galaxy and to construct a broad spectral energy distribution (SED) of the afterglow that extends the previous SED analysis based on ground-based spectroscopy. Results. We find robust evidence of a late-Time bump following the afterglow that shows evidence of a strong color change, with the spectral slope becoming flatter in the blue region of the spectrum. This bump can be interpreted as a luminous SN bump that is spectrally dissimilar to typical GRB-SNe. Correcting it for the large line-of-sight extinction makes the SN associated with GRB 140506A the most luminous detected so far. Even so, it would be in agreement with a luminosity-duration relation of GRB-SNe. Conclusions. While not supported by spectroscopic evidence, it is likely the bump following GRB 140506A is the signature of an SN that is spectrally dissimilar to classical GRB-SNe and more similar to SN 2011kl-while being associated with an average GRB, indicating the GRB-SN population is more diverse than previously thought and can reach luminosities comparable to those of superluminous SNe. © The Authors 2024.