Two peculiar fast transients in a strongly lensed host galaxy

April 2018 • 2018NatAs...2..324R

Authors • Rodney, S. A. • Balestra, I. • Bradac, M. • Brammer, G. • Broadhurst, T. • Caminha, G. B. • Chirivı, G. • Diego, J. M. • Filippenko, A. V. • Foley, R. J. • Graur, O. • Grillo, C. • Hemmati, S. • Hjorth, J. • Hoag, A. • Jauzac, M. • Jha, S. W. • Kawamata, R. • Kelly, P. L. • McCully, C. • Mobasher, B. • Molino, A. • Oguri, M. • Richard, J. • Riess, A. G. • Rosati, P. • Schmidt, K. B. • Selsing, J. • Sharon, K. • Strolger, L. -G. • Suyu, S. H. • Treu, T. • Weiner, B. J. • Williams, L. L. R. • Zitrin, A.

Abstract • A massive galaxy cluster can serve as a magnifying glass for distant stellar populations, as strong gravitational lensing magnifies background galaxies and exposes details that are otherwise undetectable. In time-domain astronomy, imaging programmes with a short cadence are able to detect rapidly evolving transients, previously unseen by surveys designed for slowly evolving supernovae. Here, we describe two unusual transient events discovered in a Hubble Space Telescope programme that combined these techniques with high-cadence imaging on a field with a strong-lensing galaxy cluster. These transients were faster and fainter than any supernovae, but substantially more luminous than a classical nova. We find that they can be explained as separate eruptions of a luminous blue variable star or a recurrent nova, or as an unrelated pair of stellar microlensing events. To distinguish between these hypotheses will require clarification of the cluster lens models, along with more high-cadence imaging of the field that could detect related transient episodes. This discovery suggests that the intersection of strong lensing with high-cadence transient surveys may be a fruitful path for future astrophysical transient studies.

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Shoubaneh Hemmati

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