AstroNote 2019-74

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2019-08-23 11:23:57
Type: Object/s-Discovery/Classification
TCD spectroscopic classification of the long-lived and luminous transient SN 2019hge
Authors: S. J. Prentice, K. Maguire, K. Skillen, M. R. Magee (TCD), P. Clark (QUB)
Source Group: TCD
Keywords: Supernova
We classify SN 2019hge as a supernova, most likely of type IIb. With a double-peaked light curve, rise time of over 53 days, and peak magnitude of -19.5 mag, this object is highly unusual.

SN2019hge was discovered by the Zwicky Transient Factory (ZTF19aawfbtg) on 2019-05-31 11:11:30 (UT) at 20.9 mag in the g band and was subsequently detected by ATLAS and PS1. The ZTF light curve is available here:

The light curve is double-peaked and rose to a peak apparent g-band magnitude of ~18.1 mag in ~53 days before rapidly declining some 30 days later. 

Galactic reddening in the direction of the transient is E(B-V) = 0.08 mag, assuming Rv =3.1.  The transient evolves at an almost constant colour pre-peak of g-r ~ -0.1 mag, with only a very gradual redward movement. The latest photometry shows a sudden evolution to the red. 

We observed the transient using the SPectrograph for the Rapid Acquisition of Transients (SPRAT; Piascik et al. 2014) on the Liverpool Telescope (LT; Steele 2004) on 2019-08-23 00:01:51.05 (UT) as part of the Trinity College Dublin (TCD) transient classification programme. The transient is clearly detected in the acquisition image. The spectrum displays P-Cygni features commensurate with SNe in the photospheric phase, there is no indication of host emission lines.

Comparing the observed spectrum with the templates of SNID (Blondin and Tonry, 2007) and Gelato (Harutyunyan et al., 2008, A&A, 488, 383) gives matches to SNe IIb at a redshift of 0.08 - 0.1, although the features between 4000 - 5000 Å appear similar to Fe II lines in post-peak SNe Ic-6 (e.g. SN 1994I, see Prentice & Mazzali, 2017).

The estimated redshift gives an peak absolute magnitude in g between -19.9 and -20.4 mag when correcting for Galactic extinction. This peak luminosity is far greater than that seen for typical SNe IIb and the colour evolution significantly bluer (Prentice et al. 2016, 2019).

Follow-up observations are encouraged.

Show current TNS values
CatalogNameReported RAReported DECReported Obj-TypeReported RedshiftHost NameHost RedshiftRemarksTNS RATNS DECTNS Obj-TypeTNS Redshift
TNS2019hge22:24:21.210+24:47:17.16SN IIb0.0922:24:21.201+24:47:17.19SLSN-I0.0866