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Published December 10, 2022 | metadata_only
Journal Article

Hard X-Ray Observations of the Hydrogen-poor Superluminous Supernova SN 2018hti with NuSTAR


Some hydrogen-poor superluminous supernovae are likely powered by a magnetar central engine, making their luminosity larger than common supernovae. Although a significant amount of X-ray flux is expected from the spin-down of the magnetar, direct observational evidence is still to be found, giving rise to the "missing energy" problem. Here we present NuSTAR observations of nearby SN 2018hti 2.4 yr (rest frame) after its optical peak. We expect that, by this time, the ejecta have become optically thin for photons more energetic than ∼15 keV. No flux is detected at the position of the supernova down to F_(10–30 keV) = 9.0 × 10^(−14) erg cm^(−2) s^(−1), or an upper limit of 7.9 × 10^(41) erg s^(−1) at a distance of 271 Mpc. This constrains the fraction of bolometric luminosity from the putative spinning down magnetar to be f_X ≲ 36% in the 10–30 keV range in a conservative case, f_X ≲ 11% in an optimistic case.

Additional Information

We thank the anonymous referee for the constructive review of the manuscript. We thank Cole Miller and Simone Dichiara for the useful discussions. This project was funded by NASA grant No. 80NSSC22K0063. W.L. was supported by the Lyman Spitzer, Jr. Fellowship at Princeton University. J.H. acknowledges support from an appointment to the NASA Postdoctoral Program at the Goddard Space Flight Center, administered by the ORAU through a contract with NASA.

Additional details

August 22, 2023
August 22, 2023