AstroNote 2023-339

Karambelkar et al (AstroNote 2023-335) and Sollerman et al. (TNS TR No. 195300)  reported the discovery of ZTF23absbqun / AT 2023zaw - a fast-fading, subluminous and red transient in the galaxy UGC 03048 at a distance of ~45 Mpc in the ZTF public stream of transients. 

We run the "Fastfinder" annotator on the Lasair broker that highlights rapidly rising or declining transients in the ZTF public stream (and will be implemented in Lasair-LSST). The results are available on the Lasair public page https://lasair-ztf.lsst.ac.uk (under Filters). 

Fastfinder highlighted this as  "fast fading in one or more filters. The predicted range in peak absolute magnitude (M = -15.37 +/- 0.14) lies within the "Faint-SN, Gap" regime(s)" on 11 December 2023. This is similar to the ZTFReST framwork (Andreoni & Coughlin et al., 2021) as described in Karambelkar et al., and available publicly for Lasair users. 

AT2023zaw has been covered by the ATLAS survey operations from 60282 to 60289 and combined with ZTF data this provides an almost daily coverage of the transient (with the first 5-sigma detection 3hrs after  ZTF).  There is no detection ot o >~20 AB mag on 60282.5 and 60283.4. A marginal detection is recovered with forced photometry on 60283.5 (o~19.7), indicating that the transient was rising. The combined ZTF and ATLAS lightcurves suggest a rise to r-band max of ~3-4 days, peaking with the ZTF point at r=18.2 on 60287.3.  Corresponding to M_r ~ -15.4 at the distance of 40kpc to the host UGC03048. 

The latest  photometry from ATLAS indicates o = 18.6 +/- 0.1 on  60289.5 All ATLAS data (Tonry et al. 2018) are available on the ATLAS forced photometry server : https://fallingstar.com (Smith et al. 2020, Shingles et al. 2021). 

There is significant Galactic extinction along the line of sight (Ag = 0.8, Ar=0.6 ; Schafly et al. 2011, from NED), although the transient still appears to be intrinsically red after accounting for this. The combined ATLAS and ZTF data imply a time above half maximum in the r-band of 6 days durig the rise and fall.  Further follow-up observations are ongoing with Pan-STARRS. 

The Asteroid Terrestrial-impact Last Alert System [ATLAS] project is primarily funded to search for Near-Earth asteroids through NASA grants NN12AR55G, 80NSSC18K0284, and 80NSSC18K1575; byproducts of the NEO search include images and catalogs from the survey area. This work was partially funded by Kepler/K2 grant J1944/80NSSC19K0112 and HST GO-15889, and STFC grants ST/T000198/1 and ST/S006109/1. The ATLAS science products have been made possible through the contributions of the University of Hawaii Institute for Astronomy, the Queen's University Belfast, the Space Telescope Science Institute, the South African Astronomical Observatory, and The Millennium Institute of Astrophysics (MAS), Chile. 

Lasair is supported by the UKRI Science and Technology Facilities Council and is a collaboration between the University of Edinburgh (grant ST/N002512/1) and Queen’s University Belfast (grant ST/N002520/1) within the LSST:UK Science Consortium.