ATLAS is a quadruple 0.5m telescope system with two units in Hawaii (Haleakala and Mauna Loa), and one each in Chile (El Sauce) and South Africa (Sutherland), see Tonry et al. 2018, (PASP,130:064505). With the installation of the two southern units, we are robotically surveying the whole sky with a cadence of 1 day between -50 and +50 and 2 days in the polar regions, weather permitting. More information is on the ATLAS homepage.
We discovered AT2024fkm (ATLAS24evb) on MJD = 60402.39 (2024-04-02.39) at m_o = 19.9 +/-0.1. There was no detection by ATLAS on MJD 60401.52 == 2024-04-03.52 to a forced 3-sigma limit of o > 20.8. AT2024fkm is offset by 23.1 arcsec north, 2.8.arcsec east from its likely host galaxy UGC08802;. , which is at z = 0.041 or d = 180 Mpc (from NED), implying an absolute magnitude of M = -16.5 (assuming m-M = 36.28 and foreground extinction A_o = 0.03).
After the report of Brennan et al. (AstroNote 2024-92) of the ZTF discovery of the fast fading nature of AT2024fkm (ZTF24aaifosg), we present the ATLAS forced photometry. These data were taken during a 2 week experiment during which we are using 110 second exposures rather than our usual 30 seconds, hence the sensitivity is somewhat deeper than we usually report. We find the source to be fading as follows.
| Average MJD | Mag | Magerr |
|---|---|---|
| 60401.52 | >20.76 | (3sigma limit) |
| 60402.41 | 19.90 | 0.09 |
| 60405.40 | 21.17 | 0.31 |
| 60404.55 | 21.17 | 0.51 |
| 60407.40 | 21.29 | 0.35 |
The transient faded significantly and rapidly, but the fading may have flattened. We caution these are 2-3 sigma detections and deeper data are needed to confirm. While this bears some resemblance to AT2017gfo and a kilonova explanation may be possible, the apparent flattening is consistent with shock cooling of a supernova, in which case the lightcurve may rise again.
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.
| 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 | 2024fkm [ATLAS24evb] | 13:53:08.541 | +35:43:13.78 | 0.041 | 13:53:08.564 | +35:43:14.38 | SN IIb | 0.04113 |