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[vsnet-grb-info 43124] GRB 260610B / AT2026owq: SAO RAS optical observations of possible re-brightening
by GCN Circulars 17 Jun '26

17 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44963 SUBJECT: GRB 260610B / AT2026owq: SAO RAS optical observations of possible re-brightening DATE: 26/06/17 09:33:10 GMT FROM: Alexander Moskvitin at SAO RAS <mosk(a)sao.ru> A. Moskvitin (SAO RAS), O. Maslennikova (SAO RAS), V. Goranskij (SAI MSU, SAO RAS), A. Pozanenko (IKI), A. Volnova (IKI), N. Pankov (IKI) report on behalf of GRB follow-up team We observed the field of GRB 260610B discovered by Fermi (The Fermi GBM team, GCN 44891; GCN 44901; Godwin and Meegan; GCN 44931), and also detected by SVOM (Yu et al., GCN 44944), with the Zeiss-1000 1-m telescope of SAO RAS + CCD photometer in Rc band on June 14, 15 and 16. The OT (O'Neill et al., GCN 44903; Watson et al., GCN 44905; Zhu et al., GCN 44909; Gillanders et al., GCN 44910; Akl et al., GCN 44911; O'Neill et al., GCN 44914; Moskvitin et al., GCN 44918; Jackson-Horne et al., GCN 44919; Izzo, GCN 44920; Li et al., GCN 44921; Bochenek and Perley, GCN 44927; Moskvitin et al., GCN 44929; Akl et al., GCN 44930; Bochenek and Perley, GCN 44932; Pankov et al., GCN 44946; Gillanders et al., GCN 44955; Angulo et al., GCN 44958; Dimple et al., GCN 44959) is detected in our stacked images with the following brightness: Date, UTstart, t-T0, Exp., Filter, Mag, Err., UL (mid,d) (n*s) (3-sigma) 2026-06-14 23:15:23 4.56847 15*180 Rc 21.14 0.12 22.3 2026-06-15 23:42:44 5.57617 8*180 Rc 20.98 0.17 21.8 2026-06-16 20:30:40 6.44388 3*600 Rc 21.06 0.18 21.9 This preliminary photometry is based on nearby SDSS stars (using Lupton 2005 transformation equations) and not corrected for Galactic extinction. Although we cannot directly confirm that the afterglow brightness has increased, we can observe a plateau in the afterglow light curve. View this GCN Circular online at https://gcn.nasa.gov/circulars/44963. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43123] GRB 260610B / AT2026owq: SAO RAS optical observations of possible re-brightening
by GCN Circulars 17 Jun '26

17 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44963 SUBJECT: GRB 260610B / AT2026owq: SAO RAS optical observations of possible re-brightening DATE: 26/06/17 09:33:10 GMT FROM: Alexander Moskvitin at SAO RAS <mosk(a)sao.ru> A. Moskvitin (SAO RAS), O. Maslennikova (SAO RAS), V. Goranskij (SAI MSU, SAO RAS), A. Pozanenko (IKI), A. Volnova (IKI), N. Pankov (IKI) report on behalf of GRB follow-up team We observed the field of GRB 260610B discovered by Fermi (The Fermi GBM team, GCN 44891; GCN 44901; Godwin and Meegan; GCN 44931), and also detected by SVOM (Yu et al., GCN 44944), with the Zeiss-1000 1-m telescope of SAO RAS + CCD photometer in Rc band on June 14, 15 and 16. The OT (O'Neill et al., GCN 44903; Watson et al., GCN 44905; Zhu et al., GCN 44909; Gillanders et al., GCN 44910; Akl et al., GCN 44911; O'Neill et al., GCN 44914; Moskvitin et al., GCN 44918; Jackson-Horne et al., GCN 44919; Izzo, GCN 44920; Li et al., GCN 44921; Bochenek and Perley, GCN 44927; Moskvitin et al., GCN 44929; Akl et al., GCN 44930; Bochenek and Perley, GCN 44932; Pankov et al., GCN 44946; Gillanders et al., GCN 44955; Angulo et al., GCN 44958; Dimple et al., GCN 44959) is detected in our stacked images with the following brightness: Date, UTstart, t-T0, Exp., Filter, Mag, Err., UL (mid,d) (n*s) (3-sigma) 2026-06-14 23:15:23 4.56847 15*180 Rc 21.14 0.12 22.3 2026-06-15 23:42:44 5.57617 8*180 Rc 20.98 0.17 21.8 2026-06-16 20:30:40 6.44388 3*600 Rc 21.06 0.18 21.9 This preliminary photometry is based on nearby SDSS stars (using Lupton 2005 transformation equations) and not corrected for Galactic extinction. Although we cannot directly confirm that the afterglow brightness has increased, we can observe a plateau in the afterglow light curve. View this GCN Circular online at https://gcn.nasa.gov/circulars/44963. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43122] GRB 260610B / AT2026owq: SAO RAS optical observations of possible re-brightening
by GCN Circulars 17 Jun '26

17 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44963 SUBJECT: GRB 260610B / AT2026owq: SAO RAS optical observations of possible re-brightening DATE: 26/06/17 09:33:10 GMT FROM: Alexander Moskvitin at SAO RAS <mosk(a)sao.ru> A. Moskvitin (SAO RAS), O. Maslennikova (SAO RAS), V. Goranskij (SAI MSU, SAO RAS), A. Pozanenko (IKI), A. Volnova (IKI), N. Pankov (IKI) report on behalf of GRB follow-up team We observed the field of GRB 260610B discovered by Fermi (The Fermi GBM team, GCN 44891; GCN 44901; Godwin and Meegan; GCN 44931), and also detected by SVOM (Yu et al., GCN 44944), with the Zeiss-1000 1-m telescope of SAO RAS + CCD photometer in Rc band on June 14, 15 and 16. The OT (O'Neill et al., GCN 44903; Watson et al., GCN 44905; Zhu et al., GCN 44909; Gillanders et al., GCN 44910; Akl et al., GCN 44911; O'Neill et al., GCN 44914; Moskvitin et al., GCN 44918; Jackson-Horne et al., GCN 44919; Izzo, GCN 44920; Li et al., GCN 44921; Bochenek and Perley, GCN 44927; Moskvitin et al., GCN 44929; Akl et al., GCN 44930; Bochenek and Perley, GCN 44932; Pankov et al., GCN 44946; Gillanders et al., GCN 44955; Angulo et al., GCN 44958; Dimple et al., GCN 44959) is detected in our stacked images with the following brightness: Date, UTstart, t-T0, Exp., Filter, Mag, Err., UL (mid,d) (n*s) (3-sigma) 2026-06-14 23:15:23 4.56847 15*180 Rc 21.14 0.12 22.3 2026-06-15 23:42:44 5.57617 8*180 Rc 20.98 0.17 21.8 2026-06-16 20:30:40 6.44388 3*600 Rc 21.06 0.18 21.9 This preliminary photometry is based on nearby SDSS stars (using Lupton 2005 transformation equations) and not corrected for Galactic extinction. Although we cannot directly confirm that the afterglow brightness has increased, we can observe a plateau in the afterglow light curve. View this GCN Circular online at https://gcn.nasa.gov/circulars/44963. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43121] GRB 260610B / AT2026owq: SAO RAS optical observations of possible re-brightening
by GCN Circulars 17 Jun '26

17 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44963 SUBJECT: GRB 260610B / AT2026owq: SAO RAS optical observations of possible re-brightening DATE: 26/06/17 09:33:10 GMT FROM: Alexander Moskvitin at SAO RAS <mosk(a)sao.ru> A. Moskvitin (SAO RAS), O. Maslennikova (SAO RAS), V. Goranskij (SAI MSU, SAO RAS), A. Pozanenko (IKI), A. Volnova (IKI), N. Pankov (IKI) report on behalf of GRB follow-up team We observed the field of GRB 260610B discovered by Fermi (The Fermi GBM team, GCN 44891; GCN 44901; Godwin and Meegan; GCN 44931), and also detected by SVOM (Yu et al., GCN 44944), with the Zeiss-1000 1-m telescope of SAO RAS + CCD photometer in Rc band on June 14, 15 and 16. The OT (O'Neill et al., GCN 44903; Watson et al., GCN 44905; Zhu et al., GCN 44909; Gillanders et al., GCN 44910; Akl et al., GCN 44911; O'Neill et al., GCN 44914; Moskvitin et al., GCN 44918; Jackson-Horne et al., GCN 44919; Izzo, GCN 44920; Li et al., GCN 44921; Bochenek and Perley, GCN 44927; Moskvitin et al., GCN 44929; Akl et al., GCN 44930; Bochenek and Perley, GCN 44932; Pankov et al., GCN 44946; Gillanders et al., GCN 44955; Angulo et al., GCN 44958; Dimple et al., GCN 44959) is detected in our stacked images with the following brightness: Date, UTstart, t-T0, Exp., Filter, Mag, Err., UL (mid,d) (n*s) (3-sigma) 2026-06-14 23:15:23 4.56847 15*180 Rc 21.14 0.12 22.3 2026-06-15 23:42:44 5.57617 8*180 Rc 20.98 0.17 21.8 2026-06-16 20:30:40 6.44388 3*600 Rc 21.06 0.18 21.9 This preliminary photometry is based on nearby SDSS stars (using Lupton 2005 transformation equations) and not corrected for Galactic extinction. Although we cannot directly confirm that the afterglow brightness has increased, we can observe a plateau in the afterglow light curve. View this GCN Circular online at https://gcn.nasa.gov/circulars/44963. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43120] GRB 260610B / AT2026owq: SAO RAS optical observations of possible re-brightening
by GCN Circulars 17 Jun '26

17 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44963 SUBJECT: GRB 260610B / AT2026owq: SAO RAS optical observations of possible re-brightening DATE: 26/06/17 09:33:10 GMT FROM: Alexander Moskvitin at SAO RAS <mosk(a)sao.ru> A. Moskvitin (SAO RAS), O. Maslennikova (SAO RAS), V. Goranskij (SAI MSU, SAO RAS), A. Pozanenko (IKI), A. Volnova (IKI), N. Pankov (IKI) report on behalf of GRB follow-up team We observed the field of GRB 260610B discovered by Fermi (The Fermi GBM team, GCN 44891; GCN 44901; Godwin and Meegan; GCN 44931), and also detected by SVOM (Yu et al., GCN 44944), with the Zeiss-1000 1-m telescope of SAO RAS + CCD photometer in Rc band on June 14, 15 and 16. The OT (O'Neill et al., GCN 44903; Watson et al., GCN 44905; Zhu et al., GCN 44909; Gillanders et al., GCN 44910; Akl et al., GCN 44911; O'Neill et al., GCN 44914; Moskvitin et al., GCN 44918; Jackson-Horne et al., GCN 44919; Izzo, GCN 44920; Li et al., GCN 44921; Bochenek and Perley, GCN 44927; Moskvitin et al., GCN 44929; Akl et al., GCN 44930; Bochenek and Perley, GCN 44932; Pankov et al., GCN 44946; Gillanders et al., GCN 44955; Angulo et al., GCN 44958; Dimple et al., GCN 44959) is detected in our stacked images with the following brightness: Date, UTstart, t-T0, Exp., Filter, Mag, Err., UL (mid,d) (n*s) (3-sigma) 2026-06-14 23:15:23 4.56847 15*180 Rc 21.14 0.12 22.3 2026-06-15 23:42:44 5.57617 8*180 Rc 20.98 0.17 21.8 2026-06-16 20:30:40 6.44388 3*600 Rc 21.06 0.18 21.9 This preliminary photometry is based on nearby SDSS stars (using Lupton 2005 transformation equations) and not corrected for Galactic extinction. Although we cannot directly confirm that the afterglow brightness has increased, we can observe a plateau in the afterglow light curve. View this GCN Circular online at https://gcn.nasa.gov/circulars/44963. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43119] GRB 260429A: cubesat Avion detection
by GCN Circulars 17 Jun '26

17 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44962 SUBJECT: GRB 260429A: cubesat Avion detection DATE: 26/06/17 08:30:39 GMT FROM: Andrey Bogomolov at Moscow State University <aabboogg(a)srd.sinp.msu.ru> From Andrey Bogomolov at Moscow State University <aabboogg(a)srd.sinp.msu.ru> A. Bogomolov, V. Bogomolov, A. Iyudin, S. Svertilov, N. Vasiliev on behalf of the MSU “Sozvezdie-270” team, report: At 2026-04-29 ~23:24:02 UT the short GRB 260429A (Fermi GBM detection: GCN #44425, GCN #44430, SVOM detection: GCN #44439, IPN triangulation: GCN #44459) was detected by the DeCoR-3 instrument on the cubesat Avion of the Moscow University project “Sozvezdie-270” [1]. Total amount of photons detected by Avion is 69 (energy band >30 keV), it corresponds to a fluence of ~6.2*10^(-7) erg/cm^2 in the range 30-500 keV. LC in the energy range of 30-500 keV is a single episode of ~0.5 sec duration with a maximum flux of ~16 phot/(cm^2*s). А total duration (T90) of the burst is less than ~0.5 s. The light curve obtained by Avion is available here: https://swx.sinp.msu.ru/models/grb_cat/data/pictures/GRB260429A_LC_Avion.png Parameters of GRB 260429A as well as other GRBs detected by Moscow University cubesats are listed at: https://swx.sinp.msu.ru/models/grb_cat/grb.php?lang=en Avion is one of 5 cubesats of the Moscow University project “Sozvezdie-270” [1] launched on 2023 June 27. The payload of Avion is a set of scintillation gamma-ray detectors DeCoR [2], the energy range is >30 keV, the time resolution is 0.5s. [1] Svertilov et al. 2023 https://link.springer.com/chapter/10.1007/978-3-031-50248-4_21 [2] Bogomolov et al. 2022 Universe 8, 282 https://www.mdpi.com/2218-1997/8/5/282 View this GCN Circular online at https://gcn.nasa.gov/circulars/44962. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43118] GRB 260429A: cubesat Avion detection
by GCN Circulars 17 Jun '26

17 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44962 SUBJECT: GRB 260429A: cubesat Avion detection DATE: 26/06/17 08:30:39 GMT FROM: Andrey Bogomolov at Moscow State University <aabboogg(a)srd.sinp.msu.ru> From Andrey Bogomolov at Moscow State University <aabboogg(a)srd.sinp.msu.ru> A. Bogomolov, V. Bogomolov, A. Iyudin, S. Svertilov, N. Vasiliev on behalf of the MSU “Sozvezdie-270” team, report: At 2026-04-29 ~23:24:02 UT the short GRB 260429A (Fermi GBM detection: GCN #44425, GCN #44430, SVOM detection: GCN #44439, IPN triangulation: GCN #44459) was detected by the DeCoR-3 instrument on the cubesat Avion of the Moscow University project “Sozvezdie-270” [1]. Total amount of photons detected by Avion is 69 (energy band >30 keV), it corresponds to a fluence of ~6.2*10^(-7) erg/cm^2 in the range 30-500 keV. LC in the energy range of 30-500 keV is a single episode of ~0.5 sec duration with a maximum flux of ~16 phot/(cm^2*s). А total duration (T90) of the burst is less than ~0.5 s. The light curve obtained by Avion is available here: https://swx.sinp.msu.ru/models/grb_cat/data/pictures/GRB260429A_LC_Avion.png Parameters of GRB 260429A as well as other GRBs detected by Moscow University cubesats are listed at: https://swx.sinp.msu.ru/models/grb_cat/grb.php?lang=en Avion is one of 5 cubesats of the Moscow University project “Sozvezdie-270” [1] launched on 2023 June 27. The payload of Avion is a set of scintillation gamma-ray detectors DeCoR [2], the energy range is >30 keV, the time resolution is 0.5s. [1] Svertilov et al. 2023 https://link.springer.com/chapter/10.1007/978-3-031-50248-4_21 [2] Bogomolov et al. 2022 Universe 8, 282 https://www.mdpi.com/2218-1997/8/5/282 View this GCN Circular online at https://gcn.nasa.gov/circulars/44962. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43117] GRB260616C: MAXI/GSC detection
by GCN Circulars 17 Jun '26

17 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44961 SUBJECT: GRB260616C: MAXI/GSC detection DATE: 26/06/17 03:18:02 GMT FROM: Wataru Iwakiri at Chiba University <iwakiri.wataru.buz(a)gmail.com> W. Iwakiri (Chiba U.),M. Serino(AGU), H. Negoro, M. Nakajima, K. Saito, T. Yokoyama, M. Wada (Nihon U.), T. Mihara, T. Tamagawa, N. Kawai, M. Matsuoka (RIKEN), T. Sakamoto, S. Sugita, Y. Kawakubo, H. Hiramatsu, A. Yoshida (AGU), Y. Tsuboi, Y. Ishihara, H. Ogaki (Chuo U.), M. Shidatsu, C. Kang, M. Uenishi, T. Usuki, S. Yatsuzuka, H. Aoe (Ehime U.), I. Takahashi, Y. Yatsu (Science Tokyo), S. Nakahira, S. Ueno, H. Tomida, M. Kurihara (JAXA), Y. Ueda, K. Fujiwara, S. Kobayashi (Kyoto U.), M. Yamauchi, M. Nishio, C. Hiraizumi (Miyazaki U.), K. Yamaoka (Nagoya U.), M. Sugizaki (Kanazawa U.), T. Kawamuro (Osaka U.), S. Yamada (Tohoku U), S. Ogawa (TUS) report on behalf of the MAXI team: The MAXI/GSC detected a bright uncatalogued X-ray transient source at 14:47 UT on June 16 2026. Assuming that the source flux was constant over the transit, we obtain the source position at (R.A., Dec) = (67.745 deg, 9.294 deg) = (04 30 58, +09 17 38) (J2000) with a statistical 90% C.L. elliptical error region with long and short radii of 0.39 deg and 0.3 deg, respectively. The roll angle of long axis from the north direction is 22.0 deg counterclockwise. There is an additional systematic uncertainty of 0.1 deg (90% containment radius). The X-ray flux averaged over the scan was 148 +- 33 mCrab (4.0-10.0keV, 1 sigma error). Without assumptions on the source constancy, we obtain a rectangular error box for the transient source with the following corners: (66.883, 10.254) deg = (04 27 31, +10 15 14) (J2000) (66.471, 9.596) deg = (04 25 53, +09 35 45) (J2000) (68.604, 8.290) deg = (04 34 24, +08 17 23) (J2000) (69.019, 8.945) deg = (04 36 04, +08 56 42) (J2000) A marginal excess of about 50 mCrab may be present in the previous and next MAXI scans at 13:14 UT and 16:20 UT, respectively. However, these scans were obtained during a period of large background variations, and the significance of the excesses is currently unclear. The possible presence of X-ray activity over multiple scans raises the possibility that this event is a new X-ray transient source rather than a GRB. We therefore tentatively name the source MAXI J0430+092. Multi-wavelength follow-up observations are encouraged. View this GCN Circular online at https://gcn.nasa.gov/circulars/44961. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43116] GRB260616C: MAXI/GSC detection
by GCN Circulars 17 Jun '26

17 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44961 SUBJECT: GRB260616C: MAXI/GSC detection DATE: 26/06/17 03:18:02 GMT FROM: Wataru Iwakiri at Chiba University <iwakiri.wataru.buz(a)gmail.com> W. Iwakiri (Chiba U.),M. Serino(AGU), H. Negoro, M. Nakajima, K. Saito, T. Yokoyama, M. Wada (Nihon U.), T. Mihara, T. Tamagawa, N. Kawai, M. Matsuoka (RIKEN), T. Sakamoto, S. Sugita, Y. Kawakubo, H. Hiramatsu, A. Yoshida (AGU), Y. Tsuboi, Y. Ishihara, H. Ogaki (Chuo U.), M. Shidatsu, C. Kang, M. Uenishi, T. Usuki, S. Yatsuzuka, H. Aoe (Ehime U.), I. Takahashi, Y. Yatsu (Science Tokyo), S. Nakahira, S. Ueno, H. Tomida, M. Kurihara (JAXA), Y. Ueda, K. Fujiwara, S. Kobayashi (Kyoto U.), M. Yamauchi, M. Nishio, C. Hiraizumi (Miyazaki U.), K. Yamaoka (Nagoya U.), M. Sugizaki (Kanazawa U.), T. Kawamuro (Osaka U.), S. Yamada (Tohoku U), S. Ogawa (TUS) report on behalf of the MAXI team: The MAXI/GSC detected a bright uncatalogued X-ray transient source at 14:47 UT on June 16 2026. Assuming that the source flux was constant over the transit, we obtain the source position at (R.A., Dec) = (67.745 deg, 9.294 deg) = (04 30 58, +09 17 38) (J2000) with a statistical 90% C.L. elliptical error region with long and short radii of 0.39 deg and 0.3 deg, respectively. The roll angle of long axis from the north direction is 22.0 deg counterclockwise. There is an additional systematic uncertainty of 0.1 deg (90% containment radius). The X-ray flux averaged over the scan was 148 +- 33 mCrab (4.0-10.0keV, 1 sigma error). Without assumptions on the source constancy, we obtain a rectangular error box for the transient source with the following corners: (66.883, 10.254) deg = (04 27 31, +10 15 14) (J2000) (66.471, 9.596) deg = (04 25 53, +09 35 45) (J2000) (68.604, 8.290) deg = (04 34 24, +08 17 23) (J2000) (69.019, 8.945) deg = (04 36 04, +08 56 42) (J2000) A marginal excess of about 50 mCrab may be present in the previous and next MAXI scans at 13:14 UT and 16:20 UT, respectively. However, these scans were obtained during a period of large background variations, and the significance of the excesses is currently unclear. The possible presence of X-ray activity over multiple scans raises the possibility that this event is a new X-ray transient source rather than a GRB. We therefore tentatively name the source MAXI J0430+092. Multi-wavelength follow-up observations are encouraged. View this GCN Circular online at https://gcn.nasa.gov/circulars/44961. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 43115] GRB 260616A: Fermi-LAT detection
by GCN Circulars 16 Jun '26

16 Jun '26

TITLE: GCN CIRCULAR NUMBER: 44960 SUBJECT: GRB 260616A: Fermi-LAT detection DATE: 26/06/16 23:28:45 GMT FROM: N. Di Lalla at Stanford University <niccolo.dilalla(a)stanford.edu> S. Lopez (CNRS / IN2P3), N. Di Lalla (Stanford University), R. Gupta (NASA/GSFC), F. Longo (University and INFN, Trieste), D. Depalo (Politecnico & INFN Bari), N. Omodei (Stanford University), and J. Valverde (Marquette University) report on behalf of the Fermi-LAT collaboration: At 03:21:54 UT on 16 June 2026, Fermi-LAT detected high-energy emission from GRB 260616A, which was also detected by Fermi-GBM (trigger 803272919/ 260616140, GCN #44948). The best LAT on-ground location is found to be RA, Dec = 93.53, -32.07 (J2000) with an error radius of 0.54 deg (90 % containment, statistical error only). This was 111 deg from the LAT boresight at the time of the trigger. The data from the Fermi-LAT show a significant increase in the event rate that is spatially and temporally correlated with the trigger with high significance. The photon flux above 100 MeV in the time interval 500 - 3000 s after the GBM trigger is (1.8 ± 0.6)E-6 ph/cm2/s. The estimated photon index above 100 MeV is -2.4 ± 0.4. The highest energy photon has an energy of 724 MeV and occurs at 1690 s after trigger time. The Fermi-LAT point of contact for this burst is Samantha López (lpsamy18(a)gmail.com) The Fermi-LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden. View this GCN Circular online at https://gcn.nasa.gov/circulars/44960. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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