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تسجيل مستخدم جديدA Hydrogen-Poor Superluminous Supernova with Enhanced Iron-Group Absorption: A New Link Between SLSNe and Broad-Lined Type Ic SNe
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P. K. Blanchard
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We present optical observations of the Type I superluminous supernova (SLSN-I) SN2017dwh at $z!approx!0.13$, which reached $M_{i}!approx!-21$ mag at peak. Spectra taken a few days after peak show an unusual and strong absorption line centered near 3200AA that we identify with Co II, suggesting a high fraction of synthesized $^{56}$Ni in the ejecta. By $sim!1$ month after peak, SN2017dwh became much redder than other SLSNe-I, instead strongly resembling broad-lined Type Ic supernovae (Ic-BL SNe) with clear suppression of the flux redward of $sim!5000$ AA, providing further evidence for a large mass of Fe-group elements. Late-time upper limits indicate a $^{56}$Ni mass of $lesssim 0.6$ M$_odot$, leaving open the possibility that SN2017dwh produced a $^{56}$Ni mass comparable to SN1998bw ($approx!0.4$ M$_odot$). Fitting the light curve with a combined magnetar and $^{56}$Ni model using ${tt MOSFiT}$, we find that the light curve can easily accommodate such masses without affecting the inferred magnetar parameters. We also find that SN2017dwh occurred in the least-luminous detected host galaxy to date for a SLSN-I, with $M_{B} = -13.5$ mag and an implied metallicity of $Z!sim!0.08$ $Z_odot$. The spectral properties of SN2017dwh provide new evidence linking SLSNe-I with Type Ic-BL SNe, and in particular the high Fe-group abundance may be due to enhanced $^{56}$Ni production or mixing due to asphericity. Finally, we find that SN2017dwh represents the most extreme end of a correlation between continuum shape and Co II absorption strength in the near-peak spectra of SLSNe-I, indicating that Fe-group abundance likely accounts for some of the variation in their spectral shapes.
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