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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 260604C: LAST detection of optical counterpart candidate
  2. GRB 260604C: MASTER OT J145749.59+284903.0 optical counterpart discovery
  3. Fermi GRB 260604C: Global MASTER-Net observations report
  4. Fermi GRB 260604C: Global MASTER-Net observations report
  5. SVOM GRB260604.85: Global MASTER-Net observations report
  6. GRB 260604C: SVOM detection of a long burst
  7. GRB 260604C: Fermi GBM Final Real-time Localization
  8. GRB 260515A: SVOM/VT optical detection at about 18 days post trigger
  9. GRB 260603A: NOT optical observations
  10. GRB 260603A: Simeiz Zeiss-1000 optical upper limit
  11. GRB 260604B: Fermi GBM Final Real-time Localization
  12. GRB 260601A: CALET Gamma-Ray Burst Monitor detection
  13. EP260602a: EP-FXT follow-up observation
  14. EP260603a: Global MASTER-Net observations report
  15. EP260603a: Einstein Probe detection of a fast X-ray transient
  16. EP260602d: Optical Upper limits with kinder observations
  17. GRB 260604A: Fermi GBM Final Real-time Localization
  18. EP260602b: Liverpool Telescope observations
  19. EP260602a: Liverpool Telescope optical upper limits
  20. EP260602b: Liverpool Telescope and LCO observations
  21. GRB 260603B: Fermi GBM Final Localization
  22. EP260602a: GTC and Liverpool Telescope optical observations
  23. Konus-Wind detection of GRB 260601B/EP260601a
  24. GRB 260603A: EP-FXT follow-up observation
  25. EP260601a/GRB 260601B: EP-FXT follow-up observation
  26. GRB 260601B / EP260601a: Mondy optical upper limit
  27. EP260602b: EP-FXT follow-up observation
  28. GRB 260601B/EP260601a: Glowbug gamma-ray detection
  29. GRB 260603A: Kilonova-Catcher optical upper limit
  30. GRB 260603A: SVOM/VT optical observations
  31. EP260602a: NOT NIR J-band observations
  32. GRB 260603A: SVOM/COLIBRÍ (FM-GFT) photometric redshift z = 3.57
  33. EP260602d: Einstein Probe detection of a fast X-ray transient
  34. Fermi trigger No 802141998: Global MASTER-Net observations report
  35. EP260602a: SVOM/VT optical magnitudes correction
  36. GRB 260601A: SVOM/GRM observation of a short burst
  37. EP260602c: Einstein Probe detection of a fast X-ray transient
  38. GRB 260603A: SVOM/COLIBRÍ (GFT-FM) optical counterpart candidate
  39. EP260602a: COLIBRÍ optical observations
  40. GRB260601B/EP260601a: NOT near-infrared observations
  41. SVOM GRB260603.23: Global MASTER-Net observations report
  42. GRB 260603A: SVOM detection of a burst
  43. EP260602b: Einstein Probe detection of a fast X-ray transient
  44. GRB 260601B/EP260601a: Insight-HXMT detection
  45. Fermi GRB 260602B: Global MASTER-Net observations report
  46. Fermi GRB 260602B: Global MASTER-Net observations report
  47. EP260530a: Xinglong optical spectroscopy of EP260530a / AT 2026nwl
  48. EP260602a: SVOM/VT optical candidate
  49. EP-WXT trigger 01709266414 (EP260602b): JinShan optical counterpart detection
  50. GRB 260602B: Fermi GBM Final Localization
  51. GRB 260601A: GECAM-B observation of a short burst
  52. GRB 260601B/EP260601a: J-band upper limit with WINTER
  53. EP260530a/AT 2026nwl: COLIBRÍ optical follow up
  54. EP260530a/AT 2026nwl: KAIT optical observations
  55. GRB 260602A: Fermi GBM Final Real-time Localization
  56. GRB 260601B: CALET Gamma-Ray Burst Monitor detection
  57. EP260602a: Optical upper limits with Kinder observations
  58. GRB 260601B / EP260601a: NuSTAR detection of prompt emission
  59. EP260602a: Einstein Probe detection of a fast X-ray transient
  60. GRB 260601B/EP260601a: SVOM/VT optical observations
  61. GRB 260601B/EP260601a: GECAM-B analysis suggests a possible long duration Type I burst
  62. GRB 260601B: GECAM-B detection of a burst probably associated with EP260601a
  63. EP260601a: Einstein Probe detection of an X-ray transient
  64. EP-WXT trigger 01709266307 (EP260601a): COLIBRÍ optical observations
  65. EP-WXT trigger 01709266307 (EP260601a): JinShan optical counterpart detection
  66. GRB 260601A: Glowbug gamma-ray detection of a short burst
  67. GRB 260531B: Glowbug gamma-ray detection
  68. GRB 260516D: VLA radio detection
  69. GRB 260601A: Fermi GBM Observation
  70. EP260530a/AT 2026nwl: COLIBRÍ optical observations
  71. GRB 260530C: SVOM/ECLAIRs detection of a burst through on-ground search
  72. GRB 260527A/EP260527a: Glowbug gamma-ray detection
  73. Fermi GRB 260601A: Global MASTER-Net observations report
  74. GRB 260601A: Fermi GBM Final Real-time Localization
  75. GRB 260531B: GECAM-B observation
  76. GRB 260518B: SVOM/ECLAIRs detection of a soft burst possibly associated with EP 260518a and AT 2026ndp
  77. The EP-WXT trigger 01709266272 is likely a flaring star
  78. GRB 260531C: Fermi GBM Final Localization Correction
  79. Fermi Gamma-ray Burst Monitor trigger 801900520/260531256 is not a GRB
  80. AT2026nik: EP-FXT X-ray counterpart
  81. Fermi trigger No 801900520: Global MASTER-Net observations report
  82. GRB 260531B: Fermi GBM Final Real-time Localization
  83. GRB 260531A: MAXI/GSC detection
  84. AT 2026nuz: COLIBRÍ optical observations
  85. IPN triangulation of GRB 260527A / EP260527a
  86. EP260527a/GRB 260527A: further FTW optical and NIR observations
  87. GRB 260530B: SVOM/GRM detection of a possible bright short GRB
  88. GRB 260530A: Fermi GBM Final Real-time Localization
  89. GRB 260527A / EP260527a: VLA radio detection
  90. EP260527a/GRB 260527A: optical upper limit with Kinder observations
  91. GRB 260429B / EP260429a: COLIBRÍ optical counterpart candidate
  92. GRB 260529A: GOTO tentative optical afterglow candidate
  93. GRB 260527A/EP260527a: VLT/X-shooter tentative redshift
  94. GRB 260527A/EP260527a: Insight-HXMT detection
  95. Fermi GRB 260529A: Global MASTER-Net observations report
  96. GRB 260529A: Fermi GBM Final Real-time Localization
  97. EP260526a: SVOM/VT optical upper limits
  98. GRB 260527A/EP260527a: Gemini GMOS-S Optical Observations
  99. EP260527a / GRB 260527A: VLT detection of the optical and nIR counterpart
  100. EP260527a / GRB 260527A: NOT optical observations

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