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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"

20964 results found.

  1. GRB 260211A: GOTO optical upper limit
  2. Fermi GRB 260212A: Global MASTER-Net observations report
  3. GRB 260211A: LAST optical upper limit
  4. GRB 260128B: SVOM/ECLAIRs refined analysis
  5. GRB260131A/B: 3.6m DOT Optical Observations
  6. GRB 260211A: SVOM/COLIBRÍ (FM-GFT) optical upper limits
  7. Fermi trigger No 792537871: Global MASTER-Net observations report
  8. Swift Operations Update + Community Forum (Friday, February 13 @ 10:00 AM EST)
  9. GRB 260208A: Swift UVOT detection
  10. Fermi GRB 260210C: Global MASTER-Net observations report
  11. EP260209a: LCO optical upper limits
  12. EP260210a: Global MASTER-Net observations report
  13. EP260210a: refined analysis of the EP-FXT observation
  14. EP260209a: Global MASTER-Net observations report
  15. GRB 260208A: LCO detection of the optical counterpart
  16. EP260210a: Optical upper limits with Kinder observations
  17. EP260210a: SVOM/C-GFT upper limit
  18. GRB 260204A: Swift-XRT afterglow detection
  19. GRB260208A: Liverpool Telescope optical follow-up observations
  20. Fermi GRB 260209A: Global MASTER-Net observations report
  21. GRB 260208B: Swift-XRT observations
  22. GRB 260131A/B: continued Mondy optical observations
  23. GRB 260204A: Swift/UVOT Upper Limits
  24. GRB 260208B: COLIBRÍ optical observations
  25. GRB 260208A: Mondy optical observations (duplicate submission)
  26. GRB 260208A: Mondy optical observations
  27. GRB 260208A: 1.3m DFOT optical detection
  28. GRB 260208A: COLIBRÍ optical observations
  29. GRB 260208A: NOT spectroscopic redshift z = 2.36
  30. GRB 260208A: Liverpool Telescope optical detection
  31. Fermi GRB 260208C: Global MASTER-Net observations report
  32. GRB 260208B: SVOM/VT optical candidate
  33. GRB 260208A: Zwicky Transient Facility Follow-Up of a Fermi GRB (Trigger 792220053)
  34. GRB 260208A: SVOM/VT optical observation
  35. Fermi GRB 260208D: Global MASTER-Net observations report
  36. GRB 260208A: Swift-XRT observations
  37. GRB 260208B: Swift ToO observations
  38. LAT GRB 260208B: Global MASTER-Net observations report
  39. GRB 260208A: Swift ToO observations
  40. GRB 260208A: GOTO detection of a potential optical counterpart (GOTO26aob)
  41. GRB 260208A : MASTER bright optical transient inside retracted Fermi error-box
  42. Fermi GRB 260208A: Global MASTER-Net observations report
  43. GRB 260207A : MASTER optical counterpart discovery
  44. GRB 260131A/B: Mondy and Terskol optical observations
  45. Fermi GRB 260207B: Global MASTER-Net observations report
  46. GRB 260206A: Swift-XRT observations
  47. Fermi trigger No 792135758: Global MASTER-Net observations report
  48. EP260131a: VLA detection
  49. GRB 260206A: Tiled Swift observations
  50. GRB 260204A: Swift-XRT observations
  51. GRB 260204A: LCO optical afterglow detection
  52. GRB 260204A : MASTER Global robotic net optical observations
  53. GRB 260204A: GOTO optical upper limit
  54. EP260110a: Late GTC/EMIR near-infrared observations
  55. GRB 260204A: SVOM detection of a burst
  56. GRB 260121A: 239Alferov CubeSat detection
  57. GRB 260131A/B: OHP/T193 optical observations
  58. GRB 260131A: KAIT optical observations
  59. GRB 251230A: MeerLICHT afterglow detection
  60. GRB 260131A: FTW optical and NIR observations
  61. GRB 260131A/AT2026bwg: Observations by the Zwicky Transient Facility
  62. GRB 260131A/B: GTC/OSIRIS+ redshift confimation
  63. GRB 260131A/B (AT2026bwg): J-band observations by SYSU 80cm infrared telescope
  64. GRB 260131A/B (AT2026bwg): COLIBRÍ further optical observations
  65. EP260131a: COLIBRÍ further observations
  66. GRB 260131A/B (AT2026bwg): COLIBRÍ optical observations and confirmation of fading
  67. GRB 260131A/B: GOTO candidate optical counterpart consistent with the MAXI localisation
  68. EP260131a: COLIBRÍ observations of slow optical fading
  69. EP260131a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  70. EP260131a: VLT/X-shooter spectroscopic redshift z = 0.937
  71. EP260131a: NOT early detection of the counterpart in "rapid response mode"
  72. EP260131a: COLIBRÍ optical observations of the counterpart
  73. Fermi GRB 260130A: Global MASTER-Net observations report
  74. EP260128a / GRB 260128A: NOT and TNG optical and NIR upper limits
  75. Fermi GRB 260129A: Global MASTER-Net observations report
  76. EP260128a: J band upper limit by SYSU 80cm infrared telescope
  77. GRB 260127B: Swift-XRT observations
  78. GRB 260127A: INASAN-Kislovodsk, SAO RAS, and Terskol K-800 optical observations
  79. EP260128a: NOT optical counterpart candidate
  80. EP260128a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  81. EP260128a: Liverpool Telescope optical observations and possible counterpart
  82. EP260128a: Global MASTER-Net observations report
  83. Fermi GRB 260127A: Global MASTER-Net observations report
  84. IceCube-260125A: No Candidate Transients from the Zwicky Transient Facility
  85. GRB 260127A: COLIBRÍ optical observations
  86. GRB 260127A: NOT optical observations
  87. GRB 260127B: Swift ToO observations
  88. GRB 260127B: GOTO candidate optical counterpart
  89. GRB 260127A: SVOM/C-GFT optical observations
  90. Fermi GRB 260127B: Global MASTER-Net observations report
  91. Swift GRB 260127A: Global MASTER-Net observations report
  92. GRB 260127A: LCO optical afterglow discovery
  93. GRB 260125A: Swift-XRT observations
  94. EP260126a: EP-FXT follow-up observation
  95. EP260126a: Optical upper limit with Kinder observations
  96. EP260126a: Further NOT optical upper limits
  97. EP260126a: NOT optical observations
  98. Fermi-LAT Gamma-ray Observations of IceCube-260125A
  99. GRB 260125A: NOT optical observations on GOTO26acv / AT 2026bjf
  100. GRB 251222A: SVOM/ECLAIRs refined analysis

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