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[vsnet-grb-info 41791] GRB 260208C: AstroSat CZTI detection
by GCN Circulars 10 Feb '26

10 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43685 SUBJECT: GRB 260208C: AstroSat CZTI detection DATE: 26/02/10 17:14:45 GMT FROM: Gaurav Waratkar at Caltech <gauravwaratkar(a)iitb.ac.in> M. Tembhurnikar (IUCAA), Harsha K. H. (IUCAA), S. Salunke (IUCAA), A. Arya (IITB), A. Goyal (IITB), G. Waratkar (Caltech/IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration: Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of a long GRB 260208C which was also detected by Fermi/GBM (Fermi GBM Team, GCN Circ. 43646) and SVOM/GRM (Yue Wang, GCN Circ. 43679). The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2026-02-08 15:12:17.5 UTC. The measured peak count rate associated with the burst is 99 (+40, -11) counts/s above the background in the combined data of all quadrants, with a total of 577 (+174, -169) counts. The local mean background count rate was 283 (+3, -4) counts/s. Using cumulative rates, we measure a T90 of 13 (+1, -8) s. CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project. CZTI GRB detections are reported regularly on the payload site at: http://astrosat.iucaa.in/czti/?q=grb View this GCN Circular online at https://gcn.nasa.gov/circulars/43685. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41790] EP260210a: COLIBRÍ optical upper limit
by GCN Circulars 10 Feb '26

10 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43684 SUBJECT: EP260210a: COLIBRÍ optical upper limit DATE: 26/02/10 14:47:40 GMT FROM: F. Fortin at IRAP <ffortin.sci.edu(a)gmail.com> Francis Fortin (IRAP), Edilberto Aguilar-Ruiz (UNAM), Jean-Grégoire Ducoin (CPPM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Alan M. Watson (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Asuka Kuwata (UNAM), Nikos Mandarakas (LAM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Fredd Sánchez Álvarez (UNAM), Benjamin Schneider (LAM) and Antonio de Ugarte Postigo (LAM) report: We imaged the field of the EP260210a (Shi et al., GCN Circ. 43681) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-02-10 11:13:20 to 13:11:12 UTC (from 0.83 to 2.80 hours after the trigger) and obtained 85 minutes of simultaneous exposure in the r and z filters. The data were reduced and coadded with the COLIBRÍ pipeline and analysed with STDWeb/STDPipe (Karpov 2025). The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. In the stacked image, we do not detect any new source at the FXT source position (Shi et al., GCN Circ. 43681) down to the following 5-sigma limit: r > 23.59 z > 22.15 Our upper limits are compatible with the earlier upper limits of Kang et al. (GCN Circ. 43683). We thank the staff of the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir and the COLIBRÍ and DDRAGO engineering teams. COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico. View this GCN Circular online at https://gcn.nasa.gov/circulars/43684. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41789] EP260210a: SVOM/C-GFT upper limit
by GCN Circulars 10 Feb '26

10 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43683 SUBJECT: EP260210a: SVOM/C-GFT upper limit DATE: 26/02/10 13:35:22 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> Z. Kang (CHO), C. Wu, L.P. Xin, X.H. Han, P.P. Zhang, X.M. Lu (NAOC), Z.W. Li, Y. Lv (CHO), R.S. Zhang, Y.J. Xiao, Y.L. Qiu, J. Wang, J.S. Deng, L. Huang, J.Y. Wei (NAOC) report on behalf of the SVOM/C-GFT team: We observed the field of EP260210a detected by EP/WXT (Shi et al., GCN 43681) with LATIOS on SVOM/C-GFT. Observations started at 2026-02-10T10:32:54 UTC, ~ 9.88 min after the trigger. We obtained g, r, and i-band follow-up imaging. After preliminary analysis，no credible candidate was detected within the error box provided by EP/FXT (Shi et al., GCN 43681) in our images. The 3-sigma upper limits are: | Mid_T - T0 (min) | Exposure Time (s) | Band | Upper Limit (AB) | |------------------|---------------------|------|------------------| | 36.13 | 10×60 | i | 20.02 | | 47.01 | 10×60 | g | 20.15 | | 59.39 | 10×60 | r | 20.23 | The photometry was calibrated against UCAC4 catalogue and no correction for Galactic dust extinction was applied. We thank the observation assistants Chun-Lei Guo and Yin-Huai Hao at Jilin observatory for their excellent support. The Chinese Ground Follow-up Telescope (C-GFT) for the SVOM mission is located at Jilin Station, Changchun Observatory, National Astronomical Observatories, CAS. It features two instruments: (1) CATCH at the Cassegrain focus with a 21 arcsec x 21 arcsec FOV for simultaneous g/r/i-band imaging, and (2) LATIOS, a 4k x 4k CMOS camera at the prime focus with a 1.28 deg x 1.28 deg FOV that images in g, r, and i bands via filter switching. View this GCN Circular online at https://gcn.nasa.gov/circulars/43683. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41788] GRB 260208B: refined analysis of the EP-FXT observation
by GCN Circulars 10 Feb '26

10 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43682 SUBJECT: GRB 260208B: refined analysis of the EP-FXT observation DATE: 26/02/10 12:51:13 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> S. Q. Jiang, H. N. Yang, Y. L. Wang, Y. Liu (NAO, CAS), Z. H. Yang, Q. C. Zhao (IHEP, CAS) on behalf of the Einstein Probe (EP) team: EP-FXT performed a follow-up observation on GRB 260208B (The Fermi GBM team, GCN 43638; Preis & Greiner, GCN 43639; Longo et al., GCN 43647; Sonawane et al., GCN 43649; Luo et al., GCN 43650; Harsha et al., GCN 43677) at 2026-02-09T06:37:35 (UTC), about 20.748 hours after the Fermi/GBM trigger. With a 4.6 ks exposure, the afterglow (Li et al., GCN 43659; Magnani et al., GCN 43668; Beardmore et al., GCN 43671) is clearly detected by EP-FXT. The average 0.5-10 keV spectrum can be fitted with an absorbed power law with a fixed Galactic hydrogen column density of 4.3 × 10^21 cm^-2, and a photon index of 2.01 (-0.21/+0.21). The derived average unabsorbed 0.5-10 keV flux is 7.28 (-0.81/+0.97) × 10^(-13) erg/s/cm^2. The uncertainties are at the 90% confidence level for the above parameters. Compared to the flux reported by Swift/XRT (Beardmore et al., GCN 43671), the temporal decay index is approximately -1.4. 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). View this GCN Circular online at https://gcn.nasa.gov/circulars/43682. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41787] EP260210a: Einstein Probe detection of an X-ray transient
by GCN Circulars 10 Feb '26

10 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43681 SUBJECT: EP260210a: Einstein Probe detection of an X-ray transient DATE: 26/02/10 12:13:39 GMT FROM: EP Team at NAOC/CAS <ep_ta(a)bao.ac.cn> R. Shi (PMO), Z. H. Yang, Q. C. Zhao (IHEP), G. Y. Zhao (SYSU), Y. J. Zhang (THU) and Z. X. Ling (NAOC) on behalf of the Einstein Probe (EP) team: We report on the detection of an X-ray transient by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission, designated EP260210a. The transient triggered EP-WXT (ID: 01709257873) at 2026-02-10T10:23:01 (UTC). The WXT position of the source is R.A. = 169.840 deg, DEC = 45.408 deg (J2000) with an uncertainty of 3 arcmin in radius (90% C.L. statistical and systematic). A follow-up observation with the Follow-up X-ray Telescope (FXT) was performed automatically. Within the WXT error circle, an uncatalogued X-ray source was detected at R.A. = 169.8314 deg, DEC = 45.3949 deg (J2000) with an uncertainty of 20 arcsec in radius (90% C.L. statistical and systematic). Further information will be updated when the telemetry data is received. 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). View this GCN Circular online at https://gcn.nasa.gov/circulars/43681. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41786] GRB 260207B: AstroSat CZTI detection
by GCN Circulars 10 Feb '26

10 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43680 SUBJECT: GRB 260207B: AstroSat CZTI detection DATE: 26/02/10 11:47:42 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> A. Goyal (IITB), A. Arya (IITB), S. Salunke (IUCAA), Harsha K. H. (IUCAA), M. Tembhurnikar (IUCAA), G. Waratkar (Caltech/IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration: Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of a short GRB 260207B which was also detected by Fermi GBM (Fermi GBM Team, GCN Circ. 43629) and GECAM (Zao et. al., GCN Circ. 43644). The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2026-02-07 13:12:07 UTC. The measured peak count rate associated with the burst is 1402 (+767, -219) counts/s above the background in the combined data of all four quadrants, with a total of 82 (+26, -21) counts. The local mean background count rate was 269 (+12, -45) counts/s. Using cumulative rates, we measure a T90 of 0.09 (+0.06, -0.03) s. We only observed the main emission (ME) part of the burst. The source was also detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2026-02-07 13:12:07 UTC. The measured peak count rate associated with the burst is 446 (+68, -75) counts/s above the background in the combined data of all quadrants, with a total of 630 (+143, -162) counts. The local mean background count rate was 1340 (+7, -8) counts/s. Due to the intrinsic 1 s binning of veto data, we cannot reliably estimate a T90 for our detection. CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project. CZTI GRB detections are reported regularly on the payload site at: http://astrosat.iucaa.in/czti/?q=grb View this GCN Circular online at https://gcn.nasa.gov/circulars/43680. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41785] GRB 260208C: SVOM/GRM observation
by GCN Circulars 10 Feb '26

10 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43679 SUBJECT: GRB 260208C: SVOM/GRM observation DATE: 26/02/10 11:05:49 GMT FROM: Yue Wang <m18509381757(a)163.com> SVOM/GRM team: Yue Wang, Chen-Wei Wang, Xing-Hao Luo, Shi-Jie Zheng, Yue Huang, Shao-Lin Xiong, Shuang-Nan Zhang (IHEP) SVOM/ECLAIRs team: Marius Brunet (IRAP) Report on behalf of the SVOM team: SVOM/GRM was triggered in-flight by GRB 260208C at 2026-02-08T15:12:21.000 (T0), which is also detected by Fermi/GBM (Fermi GBM team, GCN #43653). With the event-by-event data downloaded through the X-band ground station, the GRM light curve shows that this burst consists of multiple pulses with a T90 of 10 +4/-4 s in the 15-5000 keV band. The SVOM/GRM light curve can be found here: https://www.bursthub.cn//admin/static/svgrb260208C.png In addition, the position of this burst, as determined by Fermi/GBM (RA = 281.3, Dec = -49.2, Error = 2.3, GCN #43653), is located at about 107 degrees from the SVOM optical axis, which is outside the ECLAIRs field of view. With this localization, the time-averaged spectrum from T0-1 to T0+5 s is best fitted by a power law function. The power law index is -2.22 +0.13/-0.13. The event fluence (10-1000 keV) in this time interval is (4.21 +0.79/-0.72)E-06 erg/cm^2. The Space Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA, China), National Center for Space Studies (CNES, France) and the Chinese Academy of Sciences (CAS, China), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. GRM is developed by the Institute of High Energy Physics (IHEP) of CAS. The SVOM/GRM point of contact for this burst is: Yue Wang (IHEP) (yuewang(a)ihep.ac.cn) View this GCN Circular online at https://gcn.nasa.gov/circulars/43679. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41784] GRB 260204A: Swift-XRT afterglow detection
by GCN Circulars 10 Feb '26

10 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43678 SUBJECT: GRB 260204A: Swift-XRT afterglow detection DATE: 26/02/10 08:34:30 GMT FROM: Phil Evans at U of Leicester <pae9(a)star.le.ac.uk> J.P. Osborne (U. Leicester), M.G. Bernardini (INAF-OAB), E. Ambrosi (INAF-IASFPA) , M. Capalbi (INAF-OAR), D.N. Burrows (PSU), S. Lanava (PSU), S. Dichiara (PSU), K.L. Page (U. Leicester) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team: Swift-XRT has performed a second epoch of follow-up observations of GRB 260204A (Pillas et al., GCN Circ. 43613), collecting a further 2.6 ks between T0+363 ks and T0+458 ks. "Source 1" (Evans et al., GCN Circ. 43622), which corresponds to the fading optical counterpart (Li et al., GCN Circs 43620, 43623), is no longer detected and has faded with >3-sigma significance. The upper limit is 6.97e-3 ct/sec, compared to the previous detection level of 2.36 +/- 0.46 ct/sec, giving a power-law decay index of alpha >0.4. Using 1659 s of PC mode data and 1 UVOT image, we find an enhanced XRT position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 205.10623, +1.93075 which is equivalent to: RA (J2000): 13h 40m 25.49s Dec(J2000): +01d 55' 50.7" with an uncertainty of 4.4 arcsec (radius, 90% confidence). The results of the XRT-team automatic analysis are available at https://www.swift.ac.uk/xrt_products/03000405. The results of the full analysis of the XRT observations are available at https://www.swift.ac.uk/SVOM/SVOM_FIELD00057. This circular is an official product of the Swift-XRT team. View this GCN Circular online at https://gcn.nasa.gov/circulars/43678. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41783] GRB 260208B: AstroSat CZTI detection of a bright long burst
by GCN Circulars 10 Feb '26

10 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43677 SUBJECT: GRB 260208B: AstroSat CZTI detection of a bright long burst DATE: 26/02/10 02:01:04 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> Harsha K. H. (IUCAA), M. Tembhurnikar (IUCAA), S. Salunke (IUCAA), U. Pathak (IITB), A. Arya (IITB), A. Goyal (IITB), G. Waratkar (Caltech/IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration: Analysis of AstroSat CZTI data with the ML pipeline (Abraham et al., 2021, MNRAS, 504, 3084) and the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of a long, bright GRB 260208B which was also detected by Fermi/GBM (Fermi GBM Team, GCN Circ. 43638), Fermi/LAT (F. Longo et al., GCN Circ. 43647), and SVOM/GRM (SVOM GRM Team, GCN Circ. 43650). We also see a relatively faint burst episode about 100 s after the initial bright burst in both CZT & CsI detectors. The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2026-02-08 09:52:59.50 UTC. The measured peak count rate associated with the burst is 1334 (+64, -68) counts/s above the background in the combined data of all quadrants, with a total of 14112 (+381, -416) counts. The local mean background count rate was 272 (+2, -3) counts/s. Using cumulative rates, we measure a T90 of 24 (+6, -2) s. In the preliminary analysis, we find 2125 Compton events associated with this event. The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2026-02-08 09:52:58.95 UTC. The measured peak count rate associated with the burst is 3595 (+111, -118) counts/s above the background in the combined data of all quadrants, with a total of 32443 (+740, -736) counts. The local mean background count rate was 1199 (+4, -5) counts/s. We measure a T90 of 22 (+1, -1) s from the cumulative Veto light curve. CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project. CZTI GRB detections are reported regularly on the payload site at: http://astrosat.iucaa.in/czti/?q=grb View this GCN Circular online at https://gcn.nasa.gov/circulars/43677. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 41782] GRB260208A: Liverpool Telescope optical follow-up observations
by GCN Circulars 10 Feb '26

10 Feb '26

TITLE: GCN CIRCULAR NUMBER: 43676 SUBJECT: GRB260208A: Liverpool Telescope optical follow-up observations DATE: 26/02/10 00:51:14 GMT FROM: A. Bochenek at Liverpool John Moores University <a.m.bochenek(a)2023.ljmu.ac.uk> A. Bochenek, J. Wise, D. A. Perley (LJMU), report: We observed the field of GRB260208a (Fermi GBM team, GCN 43635; Sonawane et al., GCN 43642; Longo et al., GCN 43645; Luo et al., GCN 43658; Mukherjee et al. GCN 43673; Waratkar et al., GCN 43674, Cheung et al., GCN 43675) using the IO:O optical camera on the 2m robotic Liverpool Telescope. We obtained two epochs of 3x100s exposures in the SDSS r, i, z filters and 4x100s in SDSS g, starting at 2026-02-09 02:49:11 UT, approximately 21.7 hours after trigger, and the second epoch at 24.4 hours after the trigger. We report detections in stacked images in all filters at the position first reported by Lipunov et al., GCN 43640 and Wortley et al., GCN 43641, although we note some exposures were discarded due to poor seeing or telescope movement. MJD (mid) T_mid-T_0 Filter Mag. (AB) 61080.11951 21.74 h z 20.03 ± 0.16 61080.12395 21.85 h i 20.24 ± 0.25 61080.12842 21.95 h r 20.75 ± 0.10 61080.13428 22.09 h g 21.34 ± 0.24 61080.22567 24.29 h z 20.35 ± 0.11 61080.23080 24.41 h i 20.49 ± 0.09 61060.04432 24.54 h r 20.97 ± 0.15 61080.23595 24.64 h g 21.39 ± 0.14 The photometry is consistent with measurements taken at similar time by Dimple et al., GCN 43661 and Magnani et al., GCN 43664. The photometry was obtained using nearby PanSTARRS secondary standards and was not corrected for extinction. View this GCN Circular online at https://gcn.nasa.gov/circulars/43676. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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