AstroNote 2019-79

The Zwicky Transient Facility (ZTF; Bellm et al. 2019; Graham et al. 2019) first detected ZTF19abpbopt on 2019-08-09 at a magnitude of g=20.4.  The candidate was submitted to TNS via AMPEL (Nordin et al., arXiv:1904.05922) on 2019-08-11 as AT 2019neq.   A series of spectra were taken with the SED Machine (Blagorodnova et al. 2018) on the Palomar 60-inch telescope between 2019-08-11 and 2019-08-22, each showing a blue continuum with no obvious features.

We triggered a 2x900 second spectrum with SPRAT on the Liverpool Telescope on 2019-08-27.  The spectrum shows narrow emission lines from the host galaxy at a redshift of z=0.1075 superimposed on a blue continuum with broad, weak features.  Analyzing the spectrum using Superfit (Howell et al. 2005) finds a good match with a spectrum of the type I superluminous SN 2005ap close to maximum light at the same redshift. 

The light curve is observed to rise sharply during the first two days after the initial detection; this was followed by a two-day plateau before resuming a steady rise that continues until the present.  Imaging follow-up using IO:O on the Liverpool Telescope gives a magnitude of g = 17.20 (AB, calibrated relative to PS1) on 2019-08-27.  This corresponds to an absolute magnitude of approximately -21.2 at the measured redshift.

This is one of the nearest and brightest SLSNe in the past several years and has daily-cadence multi-color photometry tracking the rise starting from 4 magnitudes below peak.  It is in the ZTF TESS-shadowing public program (Yan et al., AstroNote #2019-51), and recovering pre-detections (or deep pre-explosion limits) from ZTF coadds before the discovery date may also be possible.  We encourage continued spectroscopic and multi-wavelength follow-up of this supernova.