We calculate the volumetric rate of superluminous supernovae ( SLSNe ) based on 5 events discovered with the ROTSE-IIIb telescope .
We gather light curves of 19 events from the literature and our own unpublished data and employ crude k-corrections to constrain the pseudo-absolute magnitude distributions in the rest frame ROTSE-IIIb ( unfiltered ) band pass for both the hydrogen poor ( SLSN-I ) and hydrogen rich ( SLSN-II ) populations .
We find that the peak magnitudes of the available SLSN-I are narrowly distributed ( M = -21.7 \pm 0.4 ) in our unfiltered band pass and may suggest an even tighter intrinsic distribution when the effects of dust are considered , although the sample may be skewed by selection and publication biases .
The presence of OII features near maximum light may uniquely signal a high luminosity event , and we suggest further observational and theoretical work is warranted to assess the possible utility of such SN 2005ap-like SLSN-I as distance indicators .
Using the pseudo-absolute magnitude distributions derived from the light curve sample , we measure the SLSN-I rate to be about ( 32 ^ { +77 } _ { -26 } ) events Gpc ^ { -3 } yr ^ { -1 } h _ { 71 } ^ { 3 } at a weighted redshift of \overline { z } = 0.17 , and the SLSN-II rate to be about ( 151 ^ { +151 } _ { -82 } ) events Gpc ^ { -3 } yr ^ { -1 } h _ { 71 } ^ { 3 } at \overline { z } = 0.15 .
Given that the exact nature and limits of these populations are still unknown , we discuss how it may be difficult to distinguish these rare SLSNe from other transient phenomena such as AGN activity and tidal disruption events even when multi-band photometry , spectroscopy , or even high resolution imaging are available .
Including one spectroscopically peculiar event , we determine a total rate for SLSN-like events of ( 199 ^ { +137 } _ { -86 } ) events Gpc ^ { -3 } yr ^ { -1 } h _ { 71 } ^ { 3 } at \overline { z } = 0.16 .