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GCN Circulars

GCN Circulars are rapid astronomical bulletins submitted by and distributed to community members worldwide. They are used to share discoveries, observations, quantitative near-term predictions, requests for follow-up observations, or future observing plans related to high-energy, multi-messenger, and variable or transient astrophysical events. See the documentation for help with subscribing to or submitting Circulars.

Search for Circulars by submitter, subject, or body text (e.g. 'Fermi GRB').
To navigate to a specific circular, enter the associated Circular ID (e.g. 'gcn123', 'Circular 123', or '123').
Advanced Search

To narrow the search results, use advanced search syntax. This allows for specifying which circular field to search (submitter, subject, and/or body). For additional information, refer to the advanced search documentation.

Advanced Search Examples (click to copy):

subject:"Swift"
body:"GRB"
submitter:"Judith Racusin"
  1. GRB 260208B: BALROG localization (Fermi Trigger 792237169 / GRB 260208412)
  2. GRB 260208B: Fermi GBM Final Real-time Localization
  3. Fermi GRB 260208A: Global MASTER-Net observations report
  4. Fermi Gamma-ray Burst Monitor trigger 792220053/260208214 is not a GRB
  5. GRB 260208A: Fermi GBM Final Real-time Localization
  6. GRB 260207B: Fermi GBM Detection of a Short Burst with Extended Emission
  7. GRB 260207A : MASTER optical counterpart discovery
  8. GRB 260131A/B: Mondy and Terskol optical observations
  9. Fermi GRB 260207B: Global MASTER-Net observations report
  10. GRB 260206A: Swift-XRT observations
  11. GRB 260207B: Fermi GBM Final Real-time Localization
  12. GRB 260207A: Fermi GBM Final Localization
  13. Fermi trigger No 792135758: Global MASTER-Net observations report
  14. EP260131a: VLA detection
  15. GRB 260206A: Tiled Swift observations
  16. GRB 260206A (or XRB from 4U 0513-40): MAXI/GSC detection
  17. GRB 260204A: SVOM/VT confirms fading of the optical afterglow
  18. GRB 260204A: Swift-XRT observations
  19. GRB 260204A: LCO optical afterglow detection
  20. GRB 260204A: SVOM/VT optical candidate
  21. GRB 260204A : MASTER Global robotic net optical observations
  22. Fermi GBM Sub-Threshold Detection of GRB 260204A
  23. GRB 260204A: GOTO optical upper limit
  24. GRB 260204A: LCO optical upper limits
  25. EP260110a: Late GTC/EMIR near-infrared observations
  26. GRB 260204B: Fermi GBM Final Real-time Localization
  27. GRB 260204A: SVOM detection of a burst
  28. GRB 260121A: 239Alferov CubeSat detection
  29. Konus-Wind detection of GRB 260121A
  30. GRB 260131A/B: OHP/T193 optical observations
  31. GRB 260131A: KAIT optical observations
  32. GRB 251230A: MeerLICHT afterglow detection
  33. GRB 260131A: FTW optical and NIR observations
  34. GRB 260131A/AT2026bwg: Observations by the Zwicky Transient Facility
  35. GRID detection of GRB 260131A/B
  36. GRB 260131A/B: GTC/OSIRIS+ redshift confimation
  37. GRB 260130A: Insight-HXMT/HE detection
  38. GRB 260130A: GECAM-B observation of a short burst
  39. GRB 260131A/B (AT2026bwg): J-band observations by SYSU 80cm infrared telescope
  40. GRB 260131A/B: EP/FXT X-ray afterglow detection
  41. GRB 260131A/B (AT2026bwg): COLIBRÍ further optical observations
  42. GRB 260127B: Insight-HXMT/HE detection
  43. GRB 260127B: GECAM-B observation of a short burst
  44. GRB 260127A: GECAM-B observation
  45. GRB 260131A: NOT spectroscopic redshift z = 1.434
  46. EP260131a: Liverpool Telescope optical upper limits
  47. EP260131a: COLIBRÍ further observations
  48. Konus-Wind detection of GRB 260128A / EP260128a
  49. GRB 260131A: Insight-HXMT/HE detection
  50. Konus-Wind detection of GRB 260131A/B
  51. EP260131a: SVOM/VT optical observation
  52. EP260131a: Xinglong optical upper limit
  53. GRB 260131A/B (AT2026bwg): COLIBRÍ optical observations and confirmation of fading
  54. GRB 260131A/B: GOTO candidate optical counterpart consistent with the MAXI localisation
  55. GRB 260131A/B: Fermi GBM Observation
  56. EP260131a: COLIBRÍ observations of slow optical fading
  57. EP260131a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  58. EP260131a: VLT/X-shooter spectroscopic redshift z = 0.937
  59. EP260131a: NOT early detection of the counterpart in "rapid response mode"
  60. GRB 260131B: MAXI/GSC detection
  61. GRB 260131A: Fermi GBM Final Real-time Localization
  62. EP260131a: COLIBRÍ optical observations of the counterpart
  63. EP260131a: Las Cumbres detection of an optical counterpart
  64. GRB 260127B: AstroSat CZTI detection
  65. GRB 260130A: Fermi GBM Detection
  66. EP260131a: Einstein Probe detection of an X-ray transient
  67. GRB 260127B: Fermi GBM Detection
  68. EP260128a / GRB 260128A: COLIBRÍ optical upper limit
  69. Fermi GRB 260130A: Global MASTER-Net observations report
  70. EP260128a / GRB 260128A: NOT and TNG optical and NIR upper limits
  71. GRB 260130A: Fermi GBM Final Real-time Localization
  72. Fermi GRB 260129A: Global MASTER-Net observations report
  73. GRB 260128B: LCO optical upper limits
  74. GRB 260128B: SVOM/COLIBRÍ (FM-GFT) optical upper limits
  75. EP260128a: J band upper limit by SYSU 80cm infrared telescope
  76. IPN triangulation of GRB 260121A
  77. GRB 260127A: Swift-BAT refined analysis
  78. GRB 260129B: Fermi GBM Final Localization
  79. GRB 260128B: SVOM detection of a burst through offline search
  80. GRB 260129A: Fermi GBM Final Localization
  81. IPN triangulation of GRB 260127B (short)
  82. GRB 260127B: Swift-XRT observations
  83. GRB 260127A: INASAN-Kislovodsk, SAO RAS, and Terskol K-800 optical observations
  84. GRB 260128A / EP260128a: Fermi-GBM Sub-Threshold Detection
  85. EP260128a: NOT optical counterpart candidate
  86. EP260128a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  87. EP260128a: Liverpool Telescope optical observations and possible counterpart
  88. EP260128a: LCO optical upper limits
  89. EP260126a: SVOM/VT optical upperlimit
  90. EP260128a: Global MASTER-Net observations report
  91. EP260128a: Einstein Probe detection of an X-ray transient
  92. Fermi GRB 260127A: Global MASTER-Net observations report
  93. IceCube-260125A: No Candidate Transients from the Zwicky Transient Facility
  94. GRB 260127A: Fermi GBM Observation
  95. IceCube-260125A: Upper limits from a search for additional neutrino events in IceCube
  96. GRB 260127A: COLIBRÍ optical observations
  97. GRB 260127A: NOT optical observations
  98. GRB 260127B: Swift ToO observations
  99. EP260126a: Seimei/TriCCS optical upper limit
  100. GRB 260127A : MITSuME Akeno optical afterglow candidate detection

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