Since the discovery of superluminous supernovae ( SLSNe ) in the last decade , it has been known that these events exhibit bluer spectral energy distributions than other supernova subtypes , with significant output in the ultraviolet .
However , the event Gaia16apd seems to outshine even the other SLSNe at rest-frame wavelengths below \sim 3000 Å . \citet yan2016 have recently presented HST UV spectra and attributed the UV flux to low iron-group abundance in the outer ejecta , and hence reduced line blanketing .
Here we present UV and optical light curves over a longer baseline in time , revealing a rapid decline at UV wavelengths despite a typical optical evolution .
Combining the published UV spectra with our own optical data , we demonstrate that Gaia16apd has a much hotter continuum than virtually any SLSN at maximum light , but it cools rapidly thereafter and is indistinguishable from the others by \sim 10 –15 days after peak .
Comparing the equivalent widths of UV absorption lines with those of other events , we show that the excess UV continuum is a result of a more powerful central power source , rather than a lack of UV absorption relative to other SLSNe or an additional component from interaction with the surrounding medium .
These findings strongly support the central-engine hypothesis for hydrogen-poor SLSNe .
An explosion ejecting M _ { ej } = 4.8 ( 0.2 / \kappa ) M _ { \odot } , where \kappa is the opacity in cm ^ { 2 } g ^ { -1 } , and forming a magnetar with spin period P = 2 ms , and B = 2 \times 10 ^ { 14 } G ( lower than other SLSNe with comparable rise-times ) can consistently explain the light curve evolution and high temperature at peak .
The host metallicity , Z = 0.18 Z _ { \odot } , is comparable to other SLSNe .