AstroNote 2025-190

ZTF25aaurzyo was first detected at a position (J2000) of:

RA = 19:09:04.27  (287.267780 deg)

Dec = +47:52:46.95 (47.879709 deg)

on 2025 June 12, 10:14:38 UTC by ZTF at g = 19.37 +/- 0.10 mag (MJD=60838.43). It was reported to the Transient Name Server by the Automatic Learning for the Rapid Classification of Events (ALeRCE) broker [1] and designated AT2025ngt.

The transient then brightened in g-band by 0.7 magnitudes by the next night, and then another 0.3 magnitudes by the night after.   ZTF obtained two detections at peak light: r = 18.80 +/- 0.04 (MJD=60840.32) and g = 18.60 +/- 0.07 (MJD=60840.24). Over the next five days, ZTF detected that the light curve had started declining, with a fast fade rate of 0.2 mag/day. 

From Legacy Survey DR10 [2], there is a bright (g~19.2, r~18.7) galaxy 1.4 arcseconds away from AT2025ngt.  A Next Generation Palomar Spectrograph [3] spectrum found a spectroscopic redshift of 0.097 for the bright galaxy, which would imply a peak absolute magnitude of M_g ~ -19.9 after being corrected for extinction. With a foreground extinction of E_(g-r) = 0.06 mag at this location [4], we derive an implied color of g-r = -0.26 +/- 0.08 mag from the ZTF photometry.  

Due to the fast evolution of this luminous blue transient, we encourage follow-up observations.

[1] Munoz-Arancibia et al. 2025, ALeRCE Transient Discovery Report for 2025-06-12

[2] Dey et al. 2019, AJ, 157, 168.

[3] Jiang et al. 2018, SPIE Proceedings, 10702, 107022L

[4] Schlafly, E. F., & Finkbeiner, D. P. 2011, ApJ, 737, 103

Based on observations obtained with the Samuel Oschin Telescope 48-inch and the 60-inch Telescope at the Palomar Observatory as part of the Zwicky Transient Facility project. ZTF is supported by the National Science Foundation under Grant No. AST-2034437 and a collaboration including Caltech, IPAC, the Oskar Klein Center at Stockholm University, the University of Maryland, University of California, Berkeley , the University of Wisconsin at Milwaukee, University of Warwick, Ruhr University Bochum, Cornell University, Northwestern University and Drexel University. Operations are conducted by COO, IPAC, and UW.