Spectroscopic Classification of an Optical Transient with the Lick Shane telescope

ATel #17286; Kishore C. Patra, Ryan J. Foley (UCSC)
on 14 Jul 2025; 22:45 UT
Distributed as an Instant Email Notice Supernovae
Credential Certification: Kishore Patra (kcpatra@ucsc.edu)

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We report the following classification of an optical transient from spectroscopic observations with the Kast spectrograph on the Shane telescope. The target was supplied by ATLAS. Observations were made on 2025 July 03 UT. Classification was performed with SNID (Blondin & Tonry, 2007, ApJ, 666, 1024).

 
Name        	| IAU Name  	| RA (J2000)	| Dec (J2000)	|   z	| Type	   | Phase	| Notes 
ATLAS25gku	| AT2025orm 	| 13:54:08.77   | +24:08:00.49  | 0.056	| Ia-91bg  | 16 d	| (1) 

Notes: When the redshift is given to 2 decimal places, it is derived from the SN spectrum. Otherwise, the redshift is determined from the host galaxy. (1) The spectrum is highly contaminated by galaxy light. SNID template fitting was performed after subtracting an SDSS host-galaxy template spectrum. The best-fit match was SN 1991bg at +16 days past peak brightness. The transient exhibits a red color at peak, an absolute B-band magnitude of approximately -18.4 mag, and a fast decline rate of Delta m15 (B) ~ 1.4 mag, all of which support a SN 1991bg-like subclassification.