We report the discovery of a fast-evolving red transient by the Zwicky Transient Facility (ZTF) public all-sky survey and the Liverpool Telescope (LT).
ZTF21aayokph (AT2021lfa) was discovered at the position (J2000) of:
ra = 12:32:48.725 (188.203019 deg)
dec = -01:29:22.56 (-1.489601 deg)
on 2021 May 4 by ZTF at r=18.60 +/- 0.08 mag (MJD=59338.2325) and g=18.80+/-0.11 mag (MJD=59338.3126). The last upper limits were on 2021 May 2 at g > 20.58 mag (MJD=59336.2569) and r > 20.23 mag (MJD=59336.3110). The rise rate (>0.85 mag/day) of AT2021lfa is therefore very fast. The Galactic extinction towards the direction of AT2021lfa is E(g-r)=0.02. The nearest counterpart in Legacy Survey deep imaging is 2.9 arcsec away (g=24.2, r=23.5).
The high Galactic latitude, red color, and lack of stellar counterpart or bright host galaxy motivated us to trigger follow-up observations.
Multi-band LT imaging at 15.5 hours and 19 hours after the first detection revealed rapid fading (1.9 mag/day in r-band) and colors consistent with a non-thermal SED. At the time of the most recent LT observation (at MJD 59339.04026) we measure r=20.12+/-0.04 mag and g=20.52 +/- 0.04 mag.
We did not identify any GRBs coincident with this position during the time window between the last non-detection and the first detection.
The fast rise, fast decay, red color, and lack of counterpart of AT2021lfa make it a strong candidate afterglow.
| Catalog | Name | Reported RA | Reported DEC | Reported Obj-Type | Reported Redshift | Host Name | Host Redshift | Remarks | TNS RA | TNS DEC | TNS Obj-Type | TNS Redshift |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| TNS | 2021lfa | 12:32:48.725 | -01:29:22.56 | 12:32:48.725 | -01:29:22.56 |
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