We report the observation and classification of two Type-I superluminous supernovae (SLSN-I) from our observations using the Kast Double Spectrograph on the 3.05 meter C. Donald Shane telescope at the Lick observatory on the night of 2024-07-08. Our observations were performed as part of our classification programme for transients discovered by the Zwicky Transient Facility (ZTF) Bright Tranient Survey (BTS).
On the red side detector the 300/7500 grating was used, which has a dispersion of 2.55 Å/pixel. On the blue side the 600/4310 grism was used, which has a dispersion of 1.02 Å/pixel. A slit width of 1.5" was used for all observations. Spectra were reduced using the UCSC Spectral Pipeline (Siebert et al. 2019). A spectral range of approximately 3580-10075 Å was obtained for the reduced spectra.
Classifications were performed by matching observed spectra to template spectra from previously classified events using Next Generation Superfit (NGSF, Goldwasser et al. 2022).
Whilst 2024jlc/ZTF24aapadbb is not currently photometrically "superluminous" (M_r ~ -19.2), it spectroscopically matches previously observed SLSN-I, and if it continues to rise past M = -20 it would be the second closest observed SLSN-I by ZTF to date at a redshift of z = 0.039. The only SLSN-I observed by ZTF at a lower redshift is 2020wnt/ZTF20acjeflr at a redshift of z = 0.032, which did not display the typical OII features of SLSN-I that we see in 2024jlc/ZTF24aapadbb's spectrum (Gutiérrez et al. 2022; Tinyanont et al. 2023).
Continued follow-up of these events is encouraged.
| Catalog | Name | Reported RA | Reported DEC | Reported Obj-Type | Reported Redshift | Host Name | Host Redshift | Remarks | TNS RA | TNS DEC | TNS Obj-Type | TNS Redshift |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| TNS | 2024jlc [ZTF24aapadbb] | 15:21:58.813 | +62:48:22.75 | SLSN-I | 0.039 | First detected in ZTF g-band forced photometry on MJD 60455.21 at m_g = 20.159 ± 0.171 on the outskirts of a late-type galaxy, it has displayed a continuing slow rise of 49 days and is currently M_r ~ M_g ~ -19.2. This event was initially classified as a SN Ib by TNS Classification Report No.17368, we reclassify it as an SLSN-I based on our matches to template spectra from the previously classified SLSN-I events 2015bn and 2010md. A redshift of z = 0.0390 ± 0.0002 was obtained using narrow host H-alpha emission. Whilst this event can be spectroscopically classified as an SLSN-I, it is not currently photometrically superlumionous, and may represent a transitional event between SN Ic of regular luminosity and SLSN-I. If it continues to rise however, it would be the closest SLSN-I observed by ZTF to date. | 15:21:58.810 | +62:48:22.75 | SLSN-I | 0.039 | ||
| TNS | 2024luu [ATLAS24jjc] | 00:28:51.032 | +13:26:26.27 | SLSN-I | 0.1051 | First reported to TNS by the ATLAS survey, ZTF internal name = ZTF24aasqeih. First detected in ZTF i-band forced photometry on MJD 60477.44 at m_i = 20.377 ± 0.251 off-centre from a faint host galaxy, it rose to a peak absolute magnitude of M_g ~ -20.4 in ~10 days, followed by a ~10 day plateau and is now slowly fading. Spectrum is well-fit by template spectra from the previously classified SLSN-I events PTF10bfz, 2011ke and 2015bn. A redshift of z = 0.1051 ± 0.0001 was obtained using host galaxy emission lines in our spectrum. | 00:28:51.032 | +13:26:26.27 | SLSN-I | 0.1051 |
| File | Comments |
|---|---|
 ZTF24aasqeih.pdf | NGSF spectral template matches for 2024luu/ATLAS24jjc/ZTF24aasqeih |
| ZTF24aapadbb.pdf | NGSF spectral template matches for 2024jlc/ZTF24aapadbb |