TITLE: GCN CIRCULAR
NUMBER: 36336
SUBJECT: LIGO/Virgo/KAGRA S240422ed: DDOTI Optical Upper Limit for J-GEM24a
DATE: 24/04/27 21:34:23 GMT
FROM: Camila Angulo at UNAM <camiangulo(a)astro.unam.mx>
Camila Angulo Valdez (UNAM), Rosa L. Becerra (UTOV), Alan M. Watson (UNAM), Simone Dichiara (PSU), Eleonora Troja (UTOV), Nat Butler (ASU), William H. Lee (UNAM), Alexander Kutyrev (GSFC/UMD), Tsvetelina Dimitrova (ASU), Keneth Garcia Cifuentes (UNAM), Margarita Pereyra (UNAM) and Océlotl Lopez (UNAM) report:
Following the detection of a possible near-infrared counterpart J-GEM24a (GCN #36333) to LIGO/Virgo/KAGRA S240422ed (GCN #36236, #36240), we visually inspected the position of this candidate in the images obtained with the DDOTI wide-field imager at the Observatorio Astronomico Nacional on Sierra de San Pedro Martir (http://ddoti.astroscu.unam.mx) on the night of 2024-04-23 UTC (GCN #36256).
We found no significant optical counterparts at the position of this source in our stacked unfiltered image, down to a limiting 5-sigma AB magnitude of w=20.2.
We thank the staff of the Observatorio Astronomico Nacional in San Pedro Martir.
View this GCN Circular online at https://gcn.nasa.gov/circulars/36336.
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TITLE: GCN CIRCULAR
NUMBER: 36335
SUBJECT: EP240426b: AST3-2 optical upper limit
DATE: 24/04/27 16:54:44 GMT
FROM: Tianrui Sun at Purple Mountain Obs,CAS <trsun(a)pmo.ac.cn>
Tian-Rui Sun, Yan-Long Hua, Jin-Jun Geng, Xue-Feng Wu, Ke-Lai Meng (Purple Mountain Observatory, CAS), Xiao-Yan Li, Zheng-Yang Li, Yun Li, Xiang-Yan Yuan (Nanjing Institute of Astronomical Optics & Technology, CAS), Lifan Wang (TAMU), Xiao-Feng Wang, Mao-Kai Hu (Tsinghua University), Lei Hu (CMU) report on behalf the AST3 Team:
Following the detection of EP240426b by Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) (Pan et al. GCN 36330),
we use Antarctic Survey Telescope 3-2 at Dome A, Antarctic (Latitude -80.4173, Longitude 77.0950) for follow-up.
Our observation started on 2024-04-27T12:44:01.
No obvious optical source was detected with an uncertainty of 3 arcmin in radius.
Our detection limit on the coadded images is down to 19.2 mag for total 36x60s with filter i.
We use the ATLASREFCAT2 (Tonry et al. 2018) as the magnitude calibration reference.
We thank Prof. Michael Ashley (UNSW) for his excellent support on the operation of AST3-2.
View this GCN Circular online at https://gcn.nasa.gov/circulars/36335.
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TITLE: GCN CIRCULAR
NUMBER: 36334
SUBJECT: LIGO/Virgo/KAGRA S240422ed: Observations with 1.6m Mephisto
DATE: 24/04/27 16:18:50 GMT
FROM: Brajesh Kumar at SWIFAR, YNU <brajesh(a)ynu.edu.cn>
Yuan-Pei Yang, Xin-Lei Chen, Brajesh Kumar, Xinzhong Er, Jinghua Zhang, Prospero Lagioia Edoardo, Tianrui Sun, Guowang Du, Xiangkun Liu, Yu Wang, Gaofan Feng, Lei Yang, Xingzhu Zou, Yu Pan, Weikang Lin, Yuan Fang, Chenxu Liu, Shiyan Zhong, Xiaowei Liu (SWIFAR, YNU)
We performed simultaneous multi-band photometric observations in response to the gravitational wave candidate LIGO/Virgo/KAGRA S240422ed (GCN 36236) and the suggested X-ray counterpart (EP240426a, GCN 36313). The observation began on 2024-04-26 (12:35:44 UT) using the 1.6m Multi-channel Photometric Survey Telescope (Mephisto) of Yunnan University at Lijiang Observatory (IAU code: 044) of Yunnan Astronomical Observatories, Chinese Academy of Sciences. Multiple frames in u, v, g, r, i, and z bands were obtained in moderate sky conditions. In our preliminary analysis on co-added images, the transient (GCN 36331, GCN 36333) is not detected at the 5 sigma limit. The pre-processing and preliminary photometry of the images were done with automatic data reduction and photometry pipeline developed for the Mephisto. Here, we note that the Mephisto filter system (u, v, g, r, i, and z) mean transmission wavelengths are 345, 385, 530, 630, 837 and 945 nm and the effective band widths are 38, 37, 79, 102, 109 and 71 nm.
Start time (UT) | Filter | Mag (AB)
12:35:44 | u | >19.10
12:35:44 | g | >19.85
12:35:44 | i | >19.58
12:59:16 | v | >19.97
12:59:16 | r | >20.18
12:59:16 | z | >18.75
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Mephisto (Multi-channel Photometric Survey Telescope) is a 1.6-m wide-field multi-channel telescope, the first of its type in the world, capable of imaging the same field of view in three optical bands simultaneously. It provides real-time, high-quality colors of stellar objects. The on-site telescope assemblage and commissioning were carried out in September 2022. The first light in all three channels was achieved on 2023 December 21.
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TITLE: GCN CIRCULAR
NUMBER: 36334
SUBJECT: LIGO/Virgo/KAGRA S240422ed: Observations with 1.6m Mephisto
DATE: 24/04/27 16:18:50 GMT
FROM: Brajesh Kumar at SWIFAR, YNU <brajesh(a)ynu.edu.cn>
Yuan-Pei Yang, Xin-Lei Chen, Brajesh Kumar, Xinzhong Er, Jinghua Zhang, Prospero Lagioia Edoardo, Tianrui Sun, Guowang Du, Xiangkun Liu, Yu Wang, Gaofan Feng, Lei Yang, Xingzhu Zou, Yu Pan, Weikang Lin, Yuan Fang, Chenxu Liu, Shiyan Zhong, Xiaowei Liu (SWIFAR, YNU)
We performed simultaneous multi-band photometric observations in response to the gravitational wave candidate LIGO/Virgo/KAGRA S240422ed (GCN 36236) and the suggested X-ray counterpart (EP240426a, GCN 36313). The observation began on 2024-04-26 (12:35:44 UT) using the 1.6m Multi-channel Photometric Survey Telescope (Mephisto) of Yunnan University at Lijiang Observatory (IAU code: 044) of Yunnan Astronomical Observatories, Chinese Academy of Sciences. Multiple frames in u, v, g, r, i, and z bands were obtained in moderate sky conditions. In our preliminary analysis on co-added images, the transient (GCN 36331, GCN 36333) is not detected at the 5 sigma limit. The pre-processing and preliminary photometry of the images were done with automatic data reduction and photometry pipeline developed for the Mephisto. Here, we note that the Mephisto filter system (u, v, g, r, i, and z) mean transmission wavelengths are 345, 385, 530, 630, 837 and 945 nm and the effective band widths are 38, 37, 79, 102, 109 and 71 nm.
Start time (UT) | Filter | Mag (AB)
12:35:44 | u | >19.10
12:35:44 | g | >19.85
12:35:44 | i | >19.58
12:59:16 | v | >19.97
12:59:16 | r | >20.18
12:59:16 | z | >18.75
---------------------------------------------------------------------------------------------------------------------------------------
Mephisto (Multi-channel Photometric Survey Telescope) is a 1.6-m wide-field multi-channel telescope, the first of its type in the world, capable of imaging the same field of view in three optical bands simultaneously. It provides real-time, high-quality colors of stellar objects. The on-site telescope assemblage and commissioning were carried out in September 2022. The first light in all three channels was achieved on 2023 December 21.
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TITLE: GCN CIRCULAR
NUMBER: 36333
SUBJECT: LIGO/Virgo/KAGRA S240422ed: A transient discovered from Subaru/MOIRCS near-infrared observations by J-GEM Collaboration
DATE: 24/04/27 11:23:37 GMT
FROM: Ichiro Takahashi at Tokyo Tech <itakahashi(a)hp.phys.titech.ac.jp>
Ichiro Takahashi, Narikazu Higuchi, Mahito Sasada (Tokyo Tech), Tomoki Morokuma (ARC/Chitech), Nozomu Tominaga, Kenshi Yanagisawa, Ichi Tanaka, Michitoshi Yoshida (NAOJ), Kazuya Matsubayashi (U. of Tokyo), Hiroshi Akitaya (ARC/Chitech), Ryusei Hamada, Daisuke Suzuki (Osaka U), Hibiki Seki, Shigeaki Joshima, Haruna Hagio, Yoshiyuki Kubo (Tokyo Tech), Satoshi Honda, Jun Takahashi, Tomohito Ohshima (Univ. of Hyogo/NHAO), Koji Kawabata, Tatsuya Nakaoka (Hiroshima U.), Ryosuke Itoh (Ibara City), Mitsuru Kokubo, Natsuki Hayatsu, Hidekazu Hanayama (NAOJ), Takahiro Kanai, Yumiko Oasa (Saitama Univ.), Katsuhiro L. Murata, Kenta Taguchi, Kouji Ohta, Miho Kawabata, Keiichi Maeda (Kyoto U.), Takayoshi Kusune (Nagoya University), Yuu Niino (U. of Tokyo), Yuichiro Sekiguchi (Toho University), Masaomi Tanaka (Tohoku University), Yousuke Utsumi (SLAC) report on behalf of Japanese Collaboration for Gravitational-Wave Electro-Magnetic Follow-up (J-GEM) collaboration:
We report a transient candidate discovered in Subaru/MOIRCS near-infrared (Y and Ks bands) observations (GCN 36265, 36302), in response to the gravitational wave event LIGO/Virgo/KAGRA S240422ed (GCN 36236). The source was discovered in a Y-band image targeted for the galaxy GL080850-243120 on UT 2024-04-23. The same source was also marginally detected in the Ks-band image on the same night. No known minor planet was found in MPChecker. Assuming the association with GL080850-243120 (237 Mpc), the offset is about 39 kpc.
Name RA2000 Dec2000 Filter Mag (AB)
J-GEM24a 122.215846 -24.516465 Y 19.7
The source was not detected in our follow-up observations in Y and Ks bands on UT 2024-04-24 (GCN 36302, with limiting magnitudes of about 20 mag AB).
View this GCN Circular online at https://gcn.nasa.gov/circulars/36333.
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TITLE: GCN CIRCULAR
NUMBER: 36332
SUBJECT: LIGO/Virgo S240422ed: Swift XRT observation of EP240426a
DATE: 24/04/27 08:41:47 GMT
FROM: K.L. Page at U Leicester <klp5(a)leicester.ac.uk>
K.L. Page (U. Leicester), P.A. Evans (U. Leicester), J.A. Kennea (PSU), A.
Tohuvavohu (U. Toronto), S.B. Cenko (NASA/GSFC), R.A.J. Eyles-Ferris (U.
Leicester), A.P. Beardmore (U. Leicester), M.G. Bernardini (INAF-OAB),
A.A. Breeveld (UCL-MSSL), S. Campana (INAF-OAB), J.J. Delaunay (PSU), M.
De Pasquale (University of Messina), S. Dichiara (PSU), P. D’Avanzo
(INAF-OAB), A. D’Aì (INAF-IASFPA) , V. D’Elia (ASI-SSDC & INAF-OAR), C.
Gronwall (PSU), D. Hartmann (Clemson University), N. Klingler (NASA-GSFC /
UMBC / CRESST II), N.P.M. Kuin (UCL-MSSL), S. Laha (NASA/GSFC), S.R. Oates
(U. Birmingham), J.P. Osborne (U. Leicester), P. O’Brien (U. Leicester),
M.J. Page (UCL-MSSL), G. Raman (PSU) S. Ronchini (PSU), T. Sbarrato
(INAF-OAB), B. Sbarufatti (INAF-OAB), M.H. Siegel (PSU), G. Tagliaferri
(INAF-OAB), E. Troja (U Tor Vergata, INAF) report on behalf of the Swift
team:
Swift has conducted a follow-up observation of the candidate counterpart
EP240426a (GCN Circ. 36313), starting 28.8 ks after the EP-FXT discovery.
We detect an X-ray source 6.2" from, and thus consistent with, the
localisation reported by EP-FXT:
Source S240422ed_X255
=====================
RA: 121.85742 ( = 08h 07m 25.78s) J2000
Dec: -29.4593 ( = -29° 27′ 33.5″) J2000
Error: 5.3 (arcsec, radius, 90% confidence)
Peak Rate: 0.012 +/- 0.003 ct s^-1 (0.3-10 keV)
Peak Flux: 5.1e-13 +/- 1.3e-13 erg cm^-2 s^-1
RASS UL: 0.034 ct s^-1 (converted to XRT; 0.3-10 keV)
so the source is not above the RASS 3-sigma
upper limit
For the flux conversions and comparisons with catalogues and upper limits
from other missions given above, we assumed a power-law spectrum with
NH=3x10^20 cm^-2, and photon index (Gamma)=1.7.
However, for direct comparison with the flux of 9.2 x 10 ^-13 erg cm^-2
s^-1 given in GCN Circ. 36313, we estimate a value of 7.0 x 10^-13 erg
cm^-2 s^-1, calculated over 0.5-10 keV, using Gamma = 2.0, corrected for
the higher Galactic absorption of 4.3x10^21 cm^-2 in this direction.
The results of the XRT automated analysis, including details of the
sources detected during the follow-up of S240422ed, are online at
https://www.swift.ac.uk/LVC/S240422ed/
This circular is an official product of the Swift XRT team.
View this GCN Circular online at https://gcn.nasa.gov/circulars/36332.
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TITLE: GCN CIRCULAR
NUMBER: 36331
SUBJECT: LIGO/Virgo/KAGRA S240422ed: NOT optical observations of EP240426a
DATE: 24/04/27 08:06:42 GMT
FROM: Dong Xu at NAOC/CAS <dxu(a)nao.cas.cn>
X. Liu, Z.P. Zhu, S.Q. Jiang, J. An, S.Y. Fu, T.H. Lu, D. Xu (NAOC), J.P.U. Fynbo (DAWN/NBI), J. Terwel (NOT) report:
We observed the field of EP240426a, suggested as an X-ray counterpart candidate (Sun et ao., GCN 36313) of LIGO/Virgo/KAGRA S240422ed (LVK, GCN 36236), using the 2.56-m Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. Observations started at 20:40:24 UT on 2024-04-26 and 9x150 s frames were obtained in the Sloan z-band in a seeing ~ 0.8".
Image subtraction of the NOT stacked z-band image to the archival PanSTARRS image shows a residual source, which is positionally consistent with the one found at DECam (Hu et al., GCN 36317), very close to the nucleus of the galaxy 2MASX J08072584-2927344. The source has m(z) = 21.3 +/- 0.2 mag (AB), calibrated with the PanSTAR field. The brightness of the source is largely consistent with that by DECam (Hu et al., GCN 36317). Together with analysis of the archival NIR data (Levan et al., GCN 36325) and the radio data (Anumarlapudi et al., GCN 36329), the source is mostly likely due to AGN activity.
Moreover, we note that there is a relatively bright spot at the north-eastern edge of the galaxy in the NOT image, seemingly at the end of a tail of the galaxy. Its coordinates are R.A. = 08:07:26.13 (J2000) and Dec. = -29:27:30.85 (J2000), with m(z) ~ 21.5 mag (AB). Photometry is significantly affected by the contamination of the galaxy. Given the NOT image is deeper and has better resolution than the PanSTAR image that is used as the template, we're inclined to think the spot is due to the difference of images rather than a physical optical transient.
View this GCN Circular online at https://gcn.nasa.gov/circulars/36331.
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TITLE: GCN CIRCULAR
NUMBER: 36330
SUBJECT: EP240426b: EP-WXT detection of a new fast X-ray transient
DATE: 24/04/27 05:01:10 GMT
FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn>
X. Pan, D. H. Zhao (NAOC, CAS), J. Q. Peng (IHEP, CAS), C. C. Jin, Z. X. Ling, Y. Liu, Z. X. Ling, C. Zhang, H. Q. Cheng, W. Chen, C. Z. Cui, D. W. Fan, H. B. Hu, J. W. Hu, M. H. Huang, D. Y. Li, H. Y. Liu, M. J. Liu, Z. Z. Lv, T. Y. Lian, X. Mao, H. W. Pan, H. Sun, W. X. Wang, Y. L. Wang, Q. Y. Wu, X. P. Xu, Y. F. Xu, H. N. Yang, W. Yuan, M. Zhang, W. D. Zhang, W. J. Zhang, Z. Zhang (NAOC,CAS), Y. Chen, S. M. Jia, S. N. Zhang (IHEP, CAS), E. Kuulkers, A. Santovincenzo (ESA), P. O'Brien (Univ. of Leicester), K. Nandra, A. Rau (MPE), B. Cordier (CEA) on behalf of the Einstein Probe team
We report on the detection of a fast X-ray transient EP240426b at 2024-04-26T14:19:06 (UTC) by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission during a calibration observation. The position of the source is R.A. = 173.787 deg, DEC = -40.741 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic). The transient event lasts for ~300 seconds and has a peak flux of ~9.5 x 10^-10 erg/s/cm^2 in the 0.5-4 keV band. The averaged 0.5-4 keV spectrum can be fitted with an absorbed power law with a photon index of 1.8(-0.3/+0.3) (with the column density fixed at the Galactic value of 8.08 x 10^20 cm^-2), giving an unabsorbed flux of 3.6(-0.6/+0.6) x 10^-10 erg/s/cm2 in the 0.5-4 keV band. The 1-sigma uncertainties are given for the above parameters.
Note: EP240426b is about 40 degrees away from the 90% credible region of the recent BH-NS gravitational-wave event S240422ed (GCN 36236), therefore it is an independent source unrelated to this event.
No previously known X-ray sources at a similar flux level are found within the 3 arcmin region around the source position. Further multi-wavelength follow-up observations are encouraged to identify the nature of this X-ray flare.
The above observation was made with the WXT instrument during the commissioning phase of EP. Launched on January 9, 2024, EP is a space X-ray observatory to monitor the soft X-ray sky with X-ray follow-up capability (Yuan et al. 2022, Handbook of X-ray and Gamma-ray Astrophysics). EP is a mission of the Chinese Academy of Sciences in collaboration with ESA, MPE and CNES.
View this GCN Circular online at https://gcn.nasa.gov/circulars/36330.
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TITLE: GCN CIRCULAR
NUMBER: 36329
SUBJECT: LIGO/Virgo/KAGRA S240422ed: Archival radio detection of EP240426a
DATE: 24/04/26 23:01:02 GMT
FROM: akashjanaki98(a)gmail.com
Akash Anumarlapudi (UWM), David Kaplan (UWM), Dougal Dobie (U. Sydney/OzGrav), Tara Murphy (U. Sydney), and Emil Lenc (CSIRO), Tomas Ahumada (Caltech).
We report the radio detection of an archival source positionally consistent with the recently discovered Einstein Probe (EP) transient EP240426a (GCN 36313). EP240426a was detected as a potential counterpart to of the LIGO/Virgo/KAGRA event S240422ed (GCN 36236, GCN 36240). A coincident optical source was also detected in the error circle of EP240426a by Palmese et al. (GCN 36317). Here we report the radio observations from the Australian SKA Pathfinder (ASKAP) Variable And Slow Transients Survey (VAST; Murphy et al. 2021, PASA, 38, e054).
The field of EP240426a was observed regularly as a part of the VAST survey with a biweekly cadence starting in December 2022. We detected a persistent faint source at the location of EP240426a in all epochs. Stacking all the observations together, we find a strong radio source with a flux density of 600+/-40 uJy at a frequency of 888 MHz at this location. We also inspect the archival data from the Very Large Array Sky Survey (VLASS) and do not find a point source at this location. Using VAST and VLASS data, we infer the power-law spectral index to be steeper than -0.7, consistent with it being an AGN. We also inspect the WISE colors and using the W4 color and radio fluxes, the estimated FIR to radio ratio is consistent with FIR/radio correlation which supports the AGN hypothesis. Additionally, we analyzed the historic WISE and NEOWISE data at the source location (within 2 arcsec), and found a variable source in the W1 and W2 passbands.
The ASKAP VAST image for this event can be obtained [here](https://www.vast-survey.org/assets/images/EP240426a.jpg).
This work uses data obtained from Inyarrimanha Ilgari Bundara / the Murchison Radio-astronomy Observatory. We acknowledge the Wajarri Yamaji People as the Traditional Owners and native title holders of the Observatory site. CSIRO’s ASKAP radio telescope is part of the Australia Telescope National Facility (https://ror.org/05qajvd42). Operation of ASKAP is funded by the Australian Government with support from the National Collaborative Research Infrastructure Strategy. ASKAP uses the resources of the Pawsey Supercomputing Research Centre. Establishment of ASKAP, Inyarrimanha Ilgari Bundara, the CSIRO Murchison Radio-astronomy Observatory and the Pawsey Supercomputing Research Centre are initiatives of the Australian Government, with support from the Government of Western Australia and the Science and Industry Endowment Fund.
View this GCN Circular online at https://gcn.nasa.gov/circulars/36329.
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TITLE: GCN CIRCULAR
NUMBER: 36328
SUBJECT: LIGO/Virgo/KAGRA S240422ed: Swope Follow-up of AT2024hfq, AT2024hfr, AT2024hfs, and AT2024hfx
DATE: 24/04/26 21:52:07 GMT
FROM: Ryan Foley at UC Santa Cruz <foley(a)ucsc.edu>
A. L. Piro, J. D. Simon (Carnegie), A. Polin (Carnegie/Purdue), C. R. Burns (Carnegie), D. A. Coulter (STScI), M. R. Drout (Toronto), R. J. Foley, and C. Rojas-Bravo (UC Santa Cruz)
report on behalf of the Carnegie Gravitational wave ElectroMagnetic follow-up (CGEM) collaboration, the One-Meter Two-Hemisphere (1M2H) collaboration, and the Swope Supernova Survey:
As part of our ongoing search for optical counterparts to the candidate gravitational wave event S240422ed (GCN 36236, GCN 36240), we have obtained imaging with the 1.0m Swope telescope at Las Campanas Observatory of the sources AT2024hfq (GCN 36298, GCN 36319), AT2024hfr (GCN 36298), AT2024hfs (GCN 36298), and AT2024hfx (GCN 36303, GCN 36304, GCN 36308).
Differential PSF photometry of the candidates and local sequence stars was obtained using DAOPHOT. The local sequence photometry was calibrated using the Refcat2 catalog, transformed to the Carnegie Supernova Project (CSP) natural system. The measured magnitudes are listed in the table below. AT2024hfq has a similar magnitude to that reported two nights earlier by DECam. AT2024hfr is likely somewhat brighter than measured by DECam on the previous night. AT2024hfs is consistent with being brighter and redder than the source was on the previous two nights. AT2024hfx is brighter by ~1 sigma than measured on the previous night by PS2.
+-----------+---------------+--------+--------------------+
| ID | JD | filter | magnitude |
+-----------+---------------+--------+--------------------+
| AT2024hfq | 2460426.565 | i | 20.97 +/- 0.14 |
| AT2024hfr | 2460426.590 | i | 19.69 +/- 0.19 |
| AT2024hfs | 2460426.577 | g | 21.07 +/- 0.19 |
| AT2024hfs | 2460426.582 | i | 20.53 +/- 0.25 |
| AT2024hfx | 2460426.551 | g | 19.74 +/- 0.03 |
| AT2024hfx | 2460426.557 | i | 19.88 +/- 0.05 |
+-----------+---------------+--------+--------------------+
We thank Francesco di Mille and the rest of the LCO staff for making these observations possible.
View this GCN Circular online at https://gcn.nasa.gov/circulars/36328.
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