AstroNote 2024-158

ZTF24aascytf was discovered at a position (J2000) of:

RA = 16:42:54.450 (250.7268754 deg)

Dec = +33:44:13.03 (33.736953 deg)

on 2024 June 15, 05:13:40.995 UTC by ZTF at i = 20.15 +/- 0.32 mag (MJD=60476.21784). It was reported to the Transient Name Server and designated AT2024lhs. ZTF also obtained a detection ~4.5 hours later at g = 19.03 +/- 0.10 mag (MJD=60476.40289).

Over the next day, the transient brightened by 0.4 mag in the g-band. One day after that, the light curve had started declining, with a fast fade rate of 0.4 mag/day. The rapid evolution was flagged by several fast-transient pipelines within the ZTF collaboration, including the “'ZTF Realtime Search and Triggering” project (ZTFReST; [1]).

There is a bright (g~19, r~19) galaxy 0.4 arcseconds away from AT2024lhs, with a redshift of 0.038 from the DESI Early Data Release [2]. Correcting for a foreground extinction of E_(g-r) = 0.02 mag at this location [3], we derive an implied blue color of g-r = -0.30 +/- 0.13 mag from the ZTF photometry and a peak absolute g-band magnitude of M_g = -17.5 mag.

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

[1] Andreoni, Coughlin, et al. 2021, ApJ, 918, 63

[2] DESI Collaboration et al. 2023, arXiv:2306.06308

[3] Schlafly, E. F., & Finkbeiner, D. P. (2011), ApJ, 737, 103 

ZTF is supported by the National Science Foundation under Grants No. AST-1440341 and AST-2034437 and a collaboration including current partners 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, Cornell University, Northwestern University and Drexel University.