EDP Sciences logo
Subscriber Authentication Point
Search
Menu
Home All issues Volume 707 (March 2026) A&A, 707 (2026) C2 Full HTML
Open Access
Erratum
This article is an erratum for:
[https://doi.org/10.1051/0004-6361/202451172]

Issue
A&A
Volume 707, March 2026
Article Number C2
Number of page(s) 3
Section Extragalactic astronomy
DOI https://doi.org/10.1051/0004-6361/202659393e
Published online 03 March 2026

Erratum for: A&A, 691, A329 (2024), https://doi.org/10.1051/0004-6361/202451172

1. Revised X-ray luminosities

In the published paper, we adopted a photon index (Γ) of 2 when calculating Chandra X-ray fluxes of the luminous fast blue optical transient (LFBOT) AT2023fhn. Based on these results, we claimed that AT2023fhn was under-luminous in X-rays with respect to other LFBOTs, including the proto-typical AT2018cow (e.g. Kuin et al. 2019). When the measurements are made without fixing Γ, we obtain higher fluxes. For each epoch, we performed spectral fitting with SHERPA (Siemiginowska et al. 2024) by first modelling the background as a power law, freezing these parameters (i.e. the normalisation and photon index, Γbkg) and then modelling the spectrum at the source position as the sum of the predetermined (scaled) background and a source power law. We find that while Γ is poorly constrained (in epoch 1 we find Γbkg = 0.9 ± 0.4 and Γ = 0 . 7 − 0.5 + 0.4 Mathematical equation: $ \Gamma = 0.7^{+0.4}_{-0.5} $), this nevertheless indicates that the spectra are harder than previously assumed. The new fluxes in the 0.5–10 keV range, corrected for an X-ray absorption column density of NH = 2.6 × 1020 cm−2, are provided in Table 1. The corresponding luminosities (for a redshift z = 0.24) are shown in Fig. 1 (see also Nayana et al. 2025 and Sevilla et al. 2026, who also present new, higher fluxes), and the updated X-ray/UV ratios in Fig. 2. Given the increased luminosities, we no longer claim that AT2023fhn was sub-luminous in X-rays with respect to AT2018cow in particular. However, we note that there is still significant variation in the population (see Fig. 1).

Table 1.

Updated unabsorbed X-ray fluxes from the Chandra observations of AT 2023fhn (programme 24500143).

Thumbnail: Fig. 1. Refer to the following caption and surrounding text. Fig. 1.

Update to Fig. 7 of the original paper with the new X-ray measurements for AT2023fhn.

Thumbnail: Fig. 2. Refer to the following caption and surrounding text. Fig. 2.

Update to Fig. 8 of the original paper with the new X-ray measurements for AT2023fhn.

2. DL versus Dθ in synchrotron blast-wave modelling

In the original paper we calculated the circumstellar properties of AT2023fhn based on radio observations and synchrotron blast-wave modelling following Chevalier (1998) and DeMarchi et al. (2022). These properties included the emission radius (Rp), Lorentz factor of the outflow (Γβ), wind density parameter (Ṁ/Vw), electron density (ne), internal magnetic field (B), and internal energy of the shock (U). In these calculations, we erroneously used the angular diameter distance (Dθ). It has become clear that the correct distance to use in these calculations is the luminosity distance (DL; see also Sevilla et al. 2026) because the parameter estimation ultimately depends on luminosities (i.e. no angular extent is being directly measured). In the case of AT2023fhn at z = 0.24, Dθ = 780 Mpc and DL = 1200 Mpc (for a flat Λ cold dark matter cosmology with Ωm = 0.3 and ΩΛ = 0.7). We provide updated versions of Table 7 and Figs. 10 and 11 of the original paper in Table 2 and Figs. 3 and 4, where DL has been used instead. The derived parameter values do not change so much that our conclusions are affected, but we note that making the same error at higher redshifts would be more consequential.

Table 2.

Update to Table 7 of the original paper using DL for the parameter calculations rather than Dθ.

Thumbnail: Fig. 3. Refer to the following caption and surrounding text. Fig. 3.

Update to Fig. 10 of the original paper using DL rather than Dθ for the parameter estimation of AT2023fhn.

Thumbnail: Fig. 4. Refer to the following caption and surrounding text. Fig. 4.

Update to Fig. 10 of the original paper using DL rather than Dθ for the parameter estimation of AT2023fhn.

Acknowledgments

The authors thank Raffaella Margutti and Ben Margalit for bringing these points to our attention.

References

  1. Chevalier, R. A. 1998, ApJ, 499, 810 [NASA ADS] [CrossRef] [Google Scholar]
  2. DeMarchi, L., Margutti, R., Dittman, J., et al. 2022, ApJ, 938, 84 [NASA ADS] [CrossRef] [Google Scholar]
  3. Kuin, N. P. M., Wu, K., Oates, S., et al. 2019, MNRAS, 487, 2505 [NASA ADS] [CrossRef] [Google Scholar]
  4. Nayana, A. J., Margutti, R., Wiston, E., et al. 2025, ApJ, 993, L6 [Google Scholar]
  5. Sevilla, C., Ho, A. Y. Q., Nayana, A. J., et al. 2026, ArXiv e-prints [arXiv:2601.18926] [Google Scholar]
  6. Siemiginowska, A., Burke, D., Günther, H. M., et al. 2024, ApJS, 274, 43 [Google Scholar]

© The Authors 2026

Licence Creative CommonsOpen Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

All Tables

Table 1.

Updated unabsorbed X-ray fluxes from the Chandra observations of AT 2023fhn (programme 24500143).

In the text
Table 2.

Update to Table 7 of the original paper using DL for the parameter calculations rather than Dθ.

In the text

All Figures

Thumbnail: Fig. 1. Refer to the following caption and surrounding text. Fig. 1.

Update to Fig. 7 of the original paper with the new X-ray measurements for AT2023fhn.
In the text
Thumbnail: Fig. 2. Refer to the following caption and surrounding text. Fig. 2.

Update to Fig. 8 of the original paper with the new X-ray measurements for AT2023fhn.
In the text
Thumbnail: Fig. 3. Refer to the following caption and surrounding text. Fig. 3.

Update to Fig. 10 of the original paper using DL rather than Dθ for the parameter estimation of AT2023fhn.
In the text
Thumbnail: Fig. 4. Refer to the following caption and surrounding text. Fig. 4.

Update to Fig. 10 of the original paper using DL rather than Dθ for the parameter estimation of AT2023fhn.
In the text

Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.

Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.

Initial download of the metrics may take a while.