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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"

20958 results found.

  1. Fermi trigger No 792537871: Global MASTER-Net observations report
  2. Swift Operations Update + Community Forum (Friday, February 13 @ 10:00 AM EST)
  3. GRB 260208A: Swift UVOT detection
  4. Fermi GRB 260210C: Global MASTER-Net observations report
  5. EP260209a: LCO optical upper limits
  6. EP260210a: Global MASTER-Net observations report
  7. EP260210a: refined analysis of the EP-FXT observation
  8. EP260209a: Global MASTER-Net observations report
  9. GRB 260208A: LCO detection of the optical counterpart
  10. EP260210a: Optical upper limits with Kinder observations
  11. EP260210a: SVOM/C-GFT upper limit
  12. GRB 260204A: Swift-XRT afterglow detection
  13. GRB260208A: Liverpool Telescope optical follow-up observations
  14. Fermi GRB 260209A: Global MASTER-Net observations report
  15. GRB 260208B: Swift-XRT observations
  16. GRB 260131A/B: continued Mondy optical observations
  17. GRB 260204A: Swift/UVOT Upper Limits
  18. GRB 260208B: COLIBRÍ optical observations
  19. GRB 260208A: Mondy optical observations (duplicate submission)
  20. GRB 260208A: Mondy optical observations
  21. GRB 260208A: 1.3m DFOT optical detection
  22. GRB 260208A: COLIBRÍ optical observations
  23. GRB 260208A: NOT spectroscopic redshift z = 2.36
  24. GRB 260208A: Liverpool Telescope optical detection
  25. Fermi GRB 260208C: Global MASTER-Net observations report
  26. GRB 260208B: SVOM/VT optical candidate
  27. GRB 260208A: Zwicky Transient Facility Follow-Up of a Fermi GRB (Trigger 792220053)
  28. GRB 260208A: SVOM/VT optical observation
  29. Fermi GRB 260208D: Global MASTER-Net observations report
  30. GRB 260208A: Swift-XRT observations
  31. GRB 260208B: Swift ToO observations
  32. LAT GRB 260208B: Global MASTER-Net observations report
  33. GRB 260208A: Swift ToO observations
  34. GRB 260208A: GOTO detection of a potential optical counterpart (GOTO26aob)
  35. GRB 260208A : MASTER bright optical transient inside retracted Fermi error-box
  36. Fermi GRB 260208A: Global MASTER-Net observations report
  37. GRB 260207A : MASTER optical counterpart discovery
  38. GRB 260131A/B: Mondy and Terskol optical observations
  39. Fermi GRB 260207B: Global MASTER-Net observations report
  40. GRB 260206A: Swift-XRT observations
  41. Fermi trigger No 792135758: Global MASTER-Net observations report
  42. EP260131a: VLA detection
  43. GRB 260206A: Tiled Swift observations
  44. GRB 260204A: Swift-XRT observations
  45. GRB 260204A: LCO optical afterglow detection
  46. GRB 260204A : MASTER Global robotic net optical observations
  47. GRB 260204A: GOTO optical upper limit
  48. EP260110a: Late GTC/EMIR near-infrared observations
  49. GRB 260204A: SVOM detection of a burst
  50. GRB 260121A: 239Alferov CubeSat detection
  51. GRB 260131A/B: OHP/T193 optical observations
  52. GRB 260131A: KAIT optical observations
  53. GRB 251230A: MeerLICHT afterglow detection
  54. GRB 260131A: FTW optical and NIR observations
  55. GRB 260131A/AT2026bwg: Observations by the Zwicky Transient Facility
  56. GRB 260131A/B: GTC/OSIRIS+ redshift confimation
  57. GRB 260131A/B (AT2026bwg): J-band observations by SYSU 80cm infrared telescope
  58. GRB 260131A/B (AT2026bwg): COLIBRÍ further optical observations
  59. EP260131a: COLIBRÍ further observations
  60. GRB 260131A/B (AT2026bwg): COLIBRÍ optical observations and confirmation of fading
  61. GRB 260131A/B: GOTO candidate optical counterpart consistent with the MAXI localisation
  62. EP260131a: COLIBRÍ observations of slow optical fading
  63. EP260131a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  64. EP260131a: VLT/X-shooter spectroscopic redshift z = 0.937
  65. EP260131a: NOT early detection of the counterpart in "rapid response mode"
  66. EP260131a: COLIBRÍ optical observations of the counterpart
  67. Fermi GRB 260130A: Global MASTER-Net observations report
  68. EP260128a / GRB 260128A: NOT and TNG optical and NIR upper limits
  69. Fermi GRB 260129A: Global MASTER-Net observations report
  70. EP260128a: J band upper limit by SYSU 80cm infrared telescope
  71. GRB 260127B: Swift-XRT observations
  72. GRB 260127A: INASAN-Kislovodsk, SAO RAS, and Terskol K-800 optical observations
  73. EP260128a: NOT optical counterpart candidate
  74. EP260128a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  75. EP260128a: Liverpool Telescope optical observations and possible counterpart
  76. EP260128a: Global MASTER-Net observations report
  77. Fermi GRB 260127A: Global MASTER-Net observations report
  78. IceCube-260125A: No Candidate Transients from the Zwicky Transient Facility
  79. GRB 260127A: COLIBRÍ optical observations
  80. GRB 260127A: NOT optical observations
  81. GRB 260127B: Swift ToO observations
  82. GRB 260127B: GOTO candidate optical counterpart
  83. GRB 260127A: SVOM/C-GFT optical observations
  84. Fermi GRB 260127B: Global MASTER-Net observations report
  85. Swift GRB 260127A: Global MASTER-Net observations report
  86. GRB 260127A: LCO optical afterglow discovery
  87. GRB 260125A: Swift-XRT observations
  88. EP260126a: EP-FXT follow-up observation
  89. EP260126a: Optical upper limit with Kinder observations
  90. EP260126a: Further NOT optical upper limits
  91. EP260126a: NOT optical observations
  92. Fermi-LAT Gamma-ray Observations of IceCube-260125A
  93. GRB 260125A: NOT optical observations on GOTO26acv / AT 2026bjf
  94. GRB 251222A: SVOM/ECLAIRs refined analysis
  95. GRB 260125A: Swift ToO observations
  96. GRB 260125A: GOTO candidate optical counterpart
  97. Fermi GRB 260125B: Global MASTER-Net observations report
  98. Swift GRB260122.97: Global MASTER-Net observations report
  99. EP260119a: Assy AZT-20 optical observations
  100. IceCube-260115A: No Candidate Transients from the Zwicky Transient Facility

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