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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 260208A: Zwicky Transient Facility Follow-Up of a Fermi GRB (Trigger 792220053)
  2. GRB 260209A: Fermi GBM Final Real-time Localization
  3. GRB 260208A: SVOM/VT optical observation
  4. Fermi GRB 260208D: Global MASTER-Net observations report
  5. GRB 260208D: Fermi GBM Final Real-time Localization
  6. GRB 260208A: Swift-XRT observations
  7. GRB 260208B: Swift ToO observations
  8. GRB 260208B: SVOM/GRM observation of a bright burst
  9. GRB 260208B: Fermi GBM Detection
  10. LAT GRB 260208B: Global MASTER-Net observations report
  11. GRB 260208B: Fermi-LAT detection
  12. GRB 260208C: Fermi GBM Final Real-time Localization
  13. GRB 260208A: Fermi-LAT detection
  14. GRB 260207B: GECAM-B observation
  15. GRB 260208A: Swift ToO observations
  16. GRB 260208A: Fermi GBM Classification Correction
  17. GRB 260208A: GOTO detection of a potential optical counterpart (GOTO26aob)
  18. GRB 260208A : MASTER bright optical transient inside retracted Fermi error-box
  19. GRB 260208B: BALROG localization (Fermi Trigger 792237169 / GRB 260208412)
  20. GRB 260208B: Fermi GBM Final Real-time Localization
  21. Fermi GRB 260208A: Global MASTER-Net observations report
  22. Fermi Gamma-ray Burst Monitor trigger 792220053/260208214 is not a GRB
  23. GRB 260208A: Fermi GBM Final Real-time Localization
  24. GRB 260207B: Fermi GBM Detection of a Short Burst with Extended Emission
  25. GRB 260207A : MASTER optical counterpart discovery
  26. GRB 260131A/B: Mondy and Terskol optical observations
  27. Fermi GRB 260207B: Global MASTER-Net observations report
  28. GRB 260206A: Swift-XRT observations
  29. GRB 260207B: Fermi GBM Final Real-time Localization
  30. GRB 260207A: Fermi GBM Final Localization
  31. Fermi trigger No 792135758: Global MASTER-Net observations report
  32. EP260131a: VLA detection
  33. GRB 260206A: Tiled Swift observations
  34. GRB 260206A (or XRB from 4U 0513-40): MAXI/GSC detection
  35. GRB 260204A: SVOM/VT confirms fading of the optical afterglow
  36. GRB 260204A: Swift-XRT observations
  37. GRB 260204A: LCO optical afterglow detection
  38. GRB 260204A: SVOM/VT optical candidate
  39. GRB 260204A : MASTER Global robotic net optical observations
  40. Fermi GBM Sub-Threshold Detection of GRB 260204A
  41. GRB 260204A: GOTO optical upper limit
  42. GRB 260204A: LCO optical upper limits
  43. EP260110a: Late GTC/EMIR near-infrared observations
  44. GRB 260204B: Fermi GBM Final Real-time Localization
  45. GRB 260204A: SVOM detection of a burst
  46. GRB 260121A: 239Alferov CubeSat detection
  47. Konus-Wind detection of GRB 260121A
  48. GRB 260131A/B: OHP/T193 optical observations
  49. GRB 260131A: KAIT optical observations
  50. GRB 251230A: MeerLICHT afterglow detection
  51. GRB 260131A: FTW optical and NIR observations
  52. GRB 260131A/AT2026bwg: Observations by the Zwicky Transient Facility
  53. GRID detection of GRB 260131A/B
  54. GRB 260131A/B: GTC/OSIRIS+ redshift confimation
  55. GRB 260130A: Insight-HXMT/HE detection
  56. GRB 260130A: GECAM-B observation of a short burst
  57. GRB 260131A/B (AT2026bwg): J-band observations by SYSU 80cm infrared telescope
  58. GRB 260131A/B: EP/FXT X-ray afterglow detection
  59. GRB 260131A/B (AT2026bwg): COLIBRÍ further optical observations
  60. GRB 260127B: Insight-HXMT/HE detection
  61. GRB 260127B: GECAM-B observation of a short burst
  62. GRB 260127A: GECAM-B observation
  63. GRB 260131A: NOT spectroscopic redshift z = 1.434
  64. EP260131a: Liverpool Telescope optical upper limits
  65. EP260131a: COLIBRÍ further observations
  66. Konus-Wind detection of GRB 260128A / EP260128a
  67. GRB 260131A: Insight-HXMT/HE detection
  68. Konus-Wind detection of GRB 260131A/B
  69. EP260131a: SVOM/VT optical observation
  70. EP260131a: Xinglong optical upper limit
  71. GRB 260131A/B (AT2026bwg): COLIBRÍ optical observations and confirmation of fading
  72. GRB 260131A/B: GOTO candidate optical counterpart consistent with the MAXI localisation
  73. GRB 260131A/B: Fermi GBM Observation
  74. EP260131a: COLIBRÍ observations of slow optical fading
  75. EP260131a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  76. EP260131a: VLT/X-shooter spectroscopic redshift z = 0.937
  77. EP260131a: NOT early detection of the counterpart in "rapid response mode"
  78. GRB 260131B: MAXI/GSC detection
  79. GRB 260131A: Fermi GBM Final Real-time Localization
  80. EP260131a: COLIBRÍ optical observations of the counterpart
  81. EP260131a: Las Cumbres detection of an optical counterpart
  82. GRB 260127B: AstroSat CZTI detection
  83. GRB 260130A: Fermi GBM Detection
  84. EP260131a: Einstein Probe detection of an X-ray transient
  85. GRB 260127B: Fermi GBM Detection
  86. EP260128a / GRB 260128A: COLIBRÍ optical upper limit
  87. Fermi GRB 260130A: Global MASTER-Net observations report
  88. EP260128a / GRB 260128A: NOT and TNG optical and NIR upper limits
  89. GRB 260130A: Fermi GBM Final Real-time Localization
  90. Fermi GRB 260129A: Global MASTER-Net observations report
  91. GRB 260128B: LCO optical upper limits
  92. GRB 260128B: SVOM/COLIBRÍ (FM-GFT) optical upper limits
  93. EP260128a: J band upper limit by SYSU 80cm infrared telescope
  94. IPN triangulation of GRB 260121A
  95. GRB 260127A: Swift-BAT refined analysis
  96. GRB 260129B: Fermi GBM Final Localization
  97. GRB 260128B: SVOM detection of a burst through offline search
  98. GRB 260129A: Fermi GBM Final Localization
  99. IPN triangulation of GRB 260127B (short)
  100. GRB 260127B: Swift-XRT observations

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