The transient source AT2024fkm was first reported by ATLAS, with internal name ATLAS24evb, on 2024-04-02 09:17:13 UT. AT2024fkm was also detected by the Zwicky Transient Facility (ZTF, Bellm et al. 2019, Graham et al. 2019) on 2024-04-03 10:20:31 UT, and was assigned the internal name ZTF24aaifosg.
AT2024fkm was identified as a rapidly evolving transient by the ''ZTF Realtime Search and Triggering'' project (ZTFReST; Andreoni & Coughlin et al., 2021) within the ZTF Collaboration.
Rapid fading was observed in the g-band (0.5 mag/day), which was confirmed by photometry obtained with the Liverpool Telescope and SED Machine on the Palomar 60-inch telescope. AT2024fkm was first observed around M_g ~ -16.8 on 2024-04-03, and was measured at M_r ~ -14.91 mag on 2024-04-07 08:49:54 UT; corrected for distance and MW extinction (which is around 1.5 mag brighter than AT2017gfo at similar epochs), or 21.4 apparent mag.
AT2024fkm was spectroscopically observed on 2024-04-06 with the Nordic Optical Telescope with an exposure time of 3x1200s at an airmass of ~1 using Grism 4 and a 1.3 arcsecond wide slit.
The resulting spectrum shows an overall blue appearance, with an optical spectral energy distribution similar to optical emission from AT2017gfo around 1-3 days post merger.
We cross-matched to SNID/NGSF, no good matches were obtained, the closest matches were to Ic-BL SNe which is inconsistent with the fast lightcurve evolution.
See attached figures.
Multichromatic follow-up observations are strongly encouraged.
| 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 | Other | 0.0411 | UGC 08802 | 0.04113 | Redshift taken from host spectrum | 13:53:08.564 | +35:43:14.38 | SN IIb | 0.04113 |
| TNS | 2017gfo | 13:09:48.082 | -23:22:53.28 | Kilonova | 0.00984 | NGC 4993 | 0.009727 | 13:09:48.082 | -23:22:53.28 | Kilonova | 0.00984 |
| File | Comments |
|---|---|
 spectra.png | Spectrum of AT2024fkm is scaled (x2.4) to match spectrum of AT2017gfo by eye. |
| lightcurve.png | |
| AT2024fkm_finder.jpeg | 15s white light acquisition image from the Nordic Optical Telescope (NOT) taken on 2024-04-06 |
Comments
Mr. Seán Brennan
Sun, 04/07/2024 - 12:17
Mistake in plot: Yaxis label
Mistake in plot: Yaxis label on spectra.png should be "flux" not "flux (no fluxcal)"