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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. EP260126a: EP-FXT follow-up observation
  2. EP260126a: Optical upper limit with Kinder observations
  3. EP260126a: Liverpool Telescope optical upper limits
  4. EP260126a: Further NOT optical upper limits
  5. EP260126a: COLIBRÍ optical upper limits
  6. EP260126a: NOT optical observations
  7. EP260126a: Einstein Probe detection of a fast X-ray transient
  8. Fermi-LAT Gamma-ray Observations of IceCube-260125A
  9. GRB 260125A: NOT optical observations on GOTO26acv / AT 2026bjf
  10. Konus-Wind detection of GRB 260120B
  11. GRB 251222A: SVOM/ECLAIRs refined analysis
  12. GRB 260125A: Swift ToO observations
  13. GRB 260125A: GOTO candidate optical counterpart
  14. Fermi GRB 260125B: Global MASTER-Net observations report
  15. IceCube-260125A - IceCube observation of a high-energy neutrino candidate track-like event
  16. GRB 260125B: Fermi GBM Final Real-time Localization
  17. GRB 260125A: Fermi GBM Final Real-time Localization
  18. GRB 260114A: SVOM/VT optical upper limits
  19. GRB 260120A: AstroSat CZTI detection
  20. GRB 260122B: Swift-BAT refined analysis
  21. GRB 260120B: SVOM/GRM observation
  22. GRB 260120A: GECAM-B observation
  23. GRB 260120B: AstroSat CZTI detection
  24. GRB 260114A: Insight-HXMT/HE detection
  25. GRB 260122B: Swift detection of a burst
  26. Swift GRB260122.97: Global MASTER-Net observations report
  27. EP260119a: Assy AZT-20 optical observations
  28. EP260119a: Mondy and SAO RAS optical upper limits
  29. GRB 260122A: Fermi GBM Final Real-time Localization
  30. IceCube-260115A: No Candidate Transients from the Zwicky Transient Facility
  31. EP260119a: Xinglong optical upper limit
  32. The EP-WXT trigger 01709251871 is likely a flaring star
  33. Fermi GRB 260120C: Global MASTER-Net observations report
  34. GRB 260120B: Swift-BAT refined analysis
  35. GRB 260120B: Swift-XRT refined Analysis
  36. EP260116a: COLIBRÍ further observations
  37. GRB 251122A / EP251122a: VLT/X-shooter host redshift z = 1.765
  38. GRB 260120B: Fermi GBM Observation
  39. EP260105a: GTC/HiPERCAM optical observations
  40. GRB 260120B: Swift/UVOT Detection
  41. GRB 260120B: COLIBRÍ optical upper limits
  42. SVOM GRB260121.06: Global MASTER-Net observations report
  43. GRB 260120B: Enhanced Swift-XRT position
  44. GRB 260120B: SVOM/C-GFT optical counterpart detection
  45. GRB 260120C: Fermi GBM Final Real-time Localization
  46. GRB 260101A: 239Alferov CubeSat detection
  47. EP260116a: COLIBRÍ observations of a tentative optical rebrightening
  48. GRB 260120B: Swift detection of a burst
  49. Swift GRB260120B: Global MASTER-Net observations report
  50. GRB 260120B: Fermi GBM Final Real-time Localization
  51. EP260119A: Mondy I-Band Observations
  52. Fermi trigger No 790601190: Global MASTER-Net observations report
  53. Fermi trigger No 790570272: Global MASTER-Net observations report
  54. GRB 260114A: Swift/UVOT Upper Limits
  55. EP260119a: Liverpool Telescope optical follow-up observations
  56. GRB 251202A: further radio observations with the VLA
  57. Trigger 1442421: Swift detection of HMXB 1A 1118-61
  58. EP260119A: GTC/OSIRIS+ spectroscopic redshift z = 5.47
  59. EP260119a: KAIT optical observations
  60. GRB 260120A: Fermi GBM Final Real-time Localization
  61. EP260119a: SVOM/VT optical observation
  62. EP260119a: update of EP-FXT follow-up observation
  63. EP260119a: NOT optical observations
  64. EP260119a: SAO RAS optical observations
  65. SVOM GRB260119.92: Global MASTER-Net observations report
  66. SVOM GRB260119.92: Global MASTER-Net observations report
  67. SVOM GRB260119.90: Global MASTER-Net observations report
  68. EP260116a: COLIBRÍ detection of a fading optical source
  69. GRB 251208D: SVOM/ECLAIRs refined analysis
  70. GRB 251208D: SVOM/ECLAIRs refined analysis
  71. GRB 260117A: Swift-XRT afterglow detection
  72. EP260119a: COLIBRÍ photometric redshift z ≈ 5.6
  73. EP260119a: Global MASTER-Net observations report
  74. GRB 260115A: AstroSat CZTI detection
  75. EP260119a: LCO optical observations
  76. GRB 260117A: ZTSh optical upper limit
  77. EP260119a: COLIBRÍ optical counterpart candidate
  78. EP260119a: preliminary result from the EP-FXT observation
  79. GRB 260110A: SVOM detection of a burst through offline search
  80. EP260119a: EP-WXT detection of a fast X-ray transient
  81. Swift GRB260118.48: Global MASTER-Net observations report
  82. GRB 260117A: SVOM/COLIBRÍ (FM-GFT) optical observations
  83. SVOM GRB260117.82: Global MASTER-Net observations report
  84. Fermi-LAT Gamma-ray Observations of IceCube-260115A
  85. Swift trigger on the HMXB 1A 1118-61
  86. GRB 260117A: SVOM/VT optical candidate
  87. GRB 260117A: SVOM/C-GFT upper limit
  88. GRB 260117A: Swift-XRT observations
  89. GRB 260117A: Swift ToO observations
  90. GRB 260117A: SVOM detection of a long faint burst
  91. EP 260116a: COLIBRÍ optical upper limit
  92. Swift triggered on the HMXB 1A 1118-61
  93. GRB 260115A: GECAM-B observation
  94. FRB 20251229A: COLIBRÍ further inspection of the updated localization
  95. EP260116a: Liverpool Telescope upper limits
  96. FRB 20251229A: Updated CHIME/FRB Baseband Localization of FRB 20251229A
  97. EP260116A: 1.3m DFOT optical upper limit
  98. GRB 260114A: VLT/MUSE spectroscopic observations
  99. IceCube-260115A: Upper limits from a search for additional neutrino events in IceCube
  100. EP260116a: Global MASTER-Net observations report

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