AstroNote 2024-386

At UTC 2024-04-21 08:37:22, ZTF detected a new transient candidate (ZTF24abybgss) 0.1” offset from a possible host galaxy in SDSS and Legacy Survey.

ZTF24abygbss was discovered at a position (J2000) of:

RA = 08:21:07.47

Dec = +28:44:22.20

The transient’s peak magnitude was g = 19.1 +/- 0.1 mag, and exhibited blue colors (g - r = -0.3 mag, corrected for Milky Way extinction [1]). The transient was reported to the Transient Name Server by the Automatic Learning for the Rapid Classification of Events (ALeRCE) broker as AT2024aehp [2]. ZTF photometry observed a fade rate of 0.2 mag/day over the next five days. 

The fast fading and possible high peak luminosity from the photometric redshift of the host galaxy (SDSS z_ph = 0.17 ± 0.09, implying M < -20 mag) motivated us to trigger follow-up observations. We acquired spectroscopy of the candidate using GMOS-S at Gemini Observatory on 2024-12-23, under the target-of-opportunity program GS-2024B-Q-121 (PI Ho). The spectrum shows galactic Hɑ, [N II], and [S II] emission lines that correspond to a redshift of z=0.170 and implies a peak absolute magnitude of M_g = -20.5 AB mag for the transient.

As the absolute magnitude, blue colors, and fast fading are consistent with an FBOT similar to AT2018cow, we encourage multiwavelength follow-up observations.

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

[2] Munoz-Arancibia et al. (2024), TNS Discovery Report No. 2024-4959

We thank the Gemini Observatory staff for assistance in rapidly obtaining these observations.

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.