DRAFT
2026-03-16 09:27:44
Type: Object/s-Data/Analysis
Bibcode: 2026TNSAN..71....1L
AT 2026fns (ATLAS26cyf): Further Kinder follow-up observations reveal no continuation of the rapid decay
Authors: C.-H. Lai, A. Aryan, Y.-H. Lee, C.-S. Lin, T.-W. Chen, A. Sankar.K, M.-H. Lee, Y.-C. Pan, W.-J. Hou, H.-Y. Hsiao, H.-C. Lin, J.-K. Guo (all NCU), J. H. Gillanders, S. J. Smartt, H. F. Stevance, S. Srivastav (all Oxford), M. Nicholl, M. Fulton, K. W. Smith, C. Angus, A. Aamer (all QUB) and T. Moore (STScI) report:
Source Group: Kinder
Abstract:
We observed the previously reported (AstroNote 2026-70) transient ATLAS26cyf (AT 2026fns) with 1m LOT at the Lulin Observatory. The reported transient has magnitudes of g = 19.17 +/- 0.04 and r = 18.95 +/- 0.06 at +6.21 days since its discovery. Given the previously reported magnitude of o = 19.1 +/- 0.1 at +3.5 days, the transient does not continue to fade rapidly. This may imply a rebrightening and a shock cooling signature rather than an LFBOT signature.

We report the photometric follow-up observations of ATLAS26cyf (AT 2026fns) with 1m LOT at the Lulin Observatory, as part of the Kinder collaboration (Chen et al. 2025, ApJ, 983, 86, doi:10.3847/1538-4357/adb428). We obtained 300s*3 frames, each for the g-band and r-band, with the g-band observations starting at 16:45 UTC on March 15th, 2026 (MJD61114.6980), at around +6.21 days since its discovery. We utilized the astroalign (Beroiz et al. 2020, A&C, 32, 100384) and astropy (Astropy Collaboration et al. 2022, ApJ, 935, 167) packages to align and stack the individual frames. We utilized the Python-based package AutoPhOT (Brennan & Fraser, 2022, A&A, 667, A62) to perform template subtraction with the DESI Legacy Survey (Dey et al. 2019, AJ 157, 168) DR10 images using the 'SFFT' (Hu et al. 2022, ApJ, 936, 157) algorithm.

Moreover, we further used AutoPhOT to perform PSF photometry. The reported transient has (AB) magnitudes of g  = 19.17 +/- 0.04 and r = 18.95 +/- 0.06 at  +6.21 days since its discovery.  Given the previously reported magnitude of o = 19.1 +/- 0.1 at +3.5 days, the transient does not appear to continue to fade. As the ATLAS o-band is an r+i composite, the apparent flattening may suggest that the early fading is due to shock cooling (e.g., as in a IIb supernova) and disfavours a luminous fast blue optical transient as the nature of the source.  The presented magnitudes are calibrated using the field stars from the ATLAS-refcat2 catalog from MAST (Tonry J. L. et al. 2018, ApJ, 867, 105). In the direction of the transient, these magnitudes are not corrected for the expected Galactic foreground extinctions of  0.29 and 0.20 mags (Schlafly & Finkbeiner 2011) for g and r bands, respectively.

Show current TNS values
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 2026fns [ATLAS26cyf] 12:31:05.742 -31:40:57.82 12:31:05.742 -31:40:57.82 SN II 0.03
AstroNote Publication Timestamp Title Authors
2026-70 2026-03-14 23:08:23 ATLAS26cyf (AT2026fns): discovery of a fast fading transient in a faint blue host K. W. Smith, L. Eastman, S.J. Smartt (Oxford/QUB), D. R. Young, M. Nicholl, M. Fulton, M. McCollum, T. Moore, J. Weston, X. Sheng, A. Aamer, C. R. Angus, D. Magill, A. J. Smith (QUB), P. Ramsden (QUB/Birmingham), L. Shingles (GSI/QUB), S. Srivastav, H. Stevance, J. Gillanders, A. J. Cooper, F. Stoppa, J. Tweddle, (Oxford), L. Rhodes (TSI/McGill), L. Denneau, J. Tonry, H. Weiland, R. Siverd (IfA, University of Hawaii), N. Erasmus, W. Koorts (South African Astronomical Observatory), A. Jordan, V. Suc (UAI, Obstech), M. R. Alarcón, J. Licandro, P. Nichita (IAC), A. Rest (STScI), T.-W. Chen (NCU), C. Stubbs (Harvard), J. Sommer (LMU), B. P. Schmidt (ANU)

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