NuSTAR observations of the FBOT AT2024qfm (Fulton et al., AstroNote 2024-206) obtained at ~9 days rest-frame after first optical detection revealed the presence of a bright hard X-ray source with a 3-30 keV flux of 5.3e-13 erg/s/cm2 (luminosity of 8e43 erg/s at the distance of AT2024qfm; Gillanders et al., AstroNote 2024-210). AT2024qfm is only the second FBOT with well detected hard X-ray emission, after the prototypical event AT2018cow (Margutti et al., 2019, ApJ, 872, 18), and it is more luminous than AT2018cow at the same epoch. We further report evidence for soft X-ray variability on a time-scale of roughly one day based on Swift-XRT observations of AT2024qfm (e.g., obs ID 00016748002 obtained on August 2 revealed 18 counts in a 20 arcsec aperture vs. the 0 counts of obs ID 00016748003 obtained on August 3 with similar aperture and exposure time corresponding to a 3 sigma upper limit of 5 counts).
We thank the entire NuSTAR and Swift teams for their extremely fast response to our triggers which enabled these observations.
| 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 | 2024qfm | 23:21:23.461 | +11:56:32.04 | 23:21:23.461 | +11:56:32.04 | |||||||
| TNS | 2018cow [ZTF18abcfcoo] | 16:16:00.220 | +22:16:04.91 | SN Ic-BL | 0.014 | 16:16:00.220 | +22:16:04.91 | SN Ic-BL | 0.014 |