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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 260204A: Swift-XRT afterglow detection
  2. GRB 260208B: AstroSat CZTI detection of a bright long burst
  3. GRB260208A: Liverpool Telescope optical follow-up observations
  4. GRB 260208A: Glowbug gamma-ray detection
  5. GRB 260208A: NuSTAR detection of prompt emission
  6. GRB 260208A: Fermi GBM Observation
  7. Fermi GRB 260209A: Global MASTER-Net observations report
  8. GRB 260208B: Swift-XRT observations
  9. GRB 260131A/B: continued Mondy optical observations
  10. GRB 260204A: Swift/UVOT Upper Limits
  11. GRB 260208B: COLIBRÍ optical observations
  12. GRB 260208A: Mondy optical observations (duplicate submission)
  13. GRB 260208A: Mondy optical observations
  14. GRB 260208A: 1.3m DFOT optical detection
  15. GRB 260208A: COLIBRÍ optical observations
  16. GRB 260208B: EP-FXT observation
  17. GRB 260208A: NOT spectroscopic redshift z = 2.36
  18. GRB 260208A: Liverpool Telescope optical detection
  19. Fermi GRB 260208C: Global MASTER-Net observations report
  20. GRB 260208B: SVOM/VT optical candidate
  21. GRB 260208A: GECAM-B observation of a bright burst
  22. GRB 260208A: Zwicky Transient Facility Follow-Up of a Fermi GRB (Trigger 792220053)
  23. GRB 260209A: Fermi GBM Final Real-time Localization
  24. GRB 260208A: SVOM/VT optical observation
  25. Fermi GRB 260208D: Global MASTER-Net observations report
  26. GRB 260208D: Fermi GBM Final Real-time Localization
  27. GRB 260208A: Swift-XRT observations
  28. GRB 260208B: Swift ToO observations
  29. GRB 260208B: SVOM/GRM observation of a bright burst
  30. GRB 260208B: Fermi GBM Detection
  31. LAT GRB 260208B: Global MASTER-Net observations report
  32. GRB 260208B: Fermi-LAT detection
  33. GRB 260208C: Fermi GBM Final Real-time Localization
  34. GRB 260208A: Fermi-LAT detection
  35. GRB 260207B: GECAM-B observation
  36. GRB 260208A: Swift ToO observations
  37. GRB 260208A: Fermi GBM Classification Correction
  38. GRB 260208A: GOTO detection of a potential optical counterpart (GOTO26aob)
  39. GRB 260208A : MASTER bright optical transient inside retracted Fermi error-box
  40. GRB 260208B: BALROG localization (Fermi Trigger 792237169 / GRB 260208412)
  41. GRB 260208B: Fermi GBM Final Real-time Localization
  42. Fermi GRB 260208A: Global MASTER-Net observations report
  43. Fermi Gamma-ray Burst Monitor trigger 792220053/260208214 is not a GRB
  44. GRB 260208A: Fermi GBM Final Real-time Localization
  45. GRB 260207B: Fermi GBM Detection of a Short Burst with Extended Emission
  46. GRB 260207A : MASTER optical counterpart discovery
  47. GRB 260131A/B: Mondy and Terskol optical observations
  48. Fermi GRB 260207B: Global MASTER-Net observations report
  49. GRB 260206A: Swift-XRT observations
  50. GRB 260207B: Fermi GBM Final Real-time Localization
  51. GRB 260207A: Fermi GBM Final Localization
  52. Fermi trigger No 792135758: Global MASTER-Net observations report
  53. EP260131a: VLA detection
  54. GRB 260206A: Tiled Swift observations
  55. GRB 260206A (or XRB from 4U 0513-40): MAXI/GSC detection
  56. GRB 260204A: SVOM/VT confirms fading of the optical afterglow
  57. GRB 260204A: Swift-XRT observations
  58. GRB 260204A: LCO optical afterglow detection
  59. GRB 260204A: SVOM/VT optical candidate
  60. GRB 260204A : MASTER Global robotic net optical observations
  61. Fermi GBM Sub-Threshold Detection of GRB 260204A
  62. GRB 260204A: GOTO optical upper limit
  63. GRB 260204A: LCO optical upper limits
  64. EP260110a: Late GTC/EMIR near-infrared observations
  65. GRB 260204B: Fermi GBM Final Real-time Localization
  66. GRB 260204A: SVOM detection of a burst
  67. GRB 260121A: 239Alferov CubeSat detection
  68. Konus-Wind detection of GRB 260121A
  69. GRB 260131A/B: OHP/T193 optical observations
  70. GRB 260131A: KAIT optical observations
  71. GRB 251230A: MeerLICHT afterglow detection
  72. GRB 260131A: FTW optical and NIR observations
  73. GRB 260131A/AT2026bwg: Observations by the Zwicky Transient Facility
  74. GRID detection of GRB 260131A/B
  75. GRB 260131A/B: GTC/OSIRIS+ redshift confimation
  76. GRB 260130A: Insight-HXMT/HE detection
  77. GRB 260130A: GECAM-B observation of a short burst
  78. GRB 260131A/B (AT2026bwg): J-band observations by SYSU 80cm infrared telescope
  79. GRB 260131A/B: EP/FXT X-ray afterglow detection
  80. GRB 260131A/B (AT2026bwg): COLIBRÍ further optical observations
  81. GRB 260127B: Insight-HXMT/HE detection
  82. GRB 260127B: GECAM-B observation of a short burst
  83. GRB 260127A: GECAM-B observation
  84. GRB 260131A: NOT spectroscopic redshift z = 1.434
  85. EP260131a: Liverpool Telescope optical upper limits
  86. EP260131a: COLIBRÍ further observations
  87. Konus-Wind detection of GRB 260128A / EP260128a
  88. GRB 260131A: Insight-HXMT/HE detection
  89. Konus-Wind detection of GRB 260131A/B
  90. EP260131a: SVOM/VT optical observation
  91. EP260131a: Xinglong optical upper limit
  92. GRB 260131A/B (AT2026bwg): COLIBRÍ optical observations and confirmation of fading
  93. GRB 260131A/B: GOTO candidate optical counterpart consistent with the MAXI localisation
  94. GRB 260131A/B: Fermi GBM Observation
  95. EP260131a: COLIBRÍ observations of slow optical fading
  96. EP260131a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  97. EP260131a: VLT/X-shooter spectroscopic redshift z = 0.937
  98. EP260131a: NOT early detection of the counterpart in "rapid response mode"
  99. GRB 260131B: MAXI/GSC detection
  100. GRB 260131A: Fermi GBM Final Real-time Localization

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