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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 260411A: SVOM/GRM observation
  2. GRB 260407B: SVOM/GRM detection of a possible magnetar X-ray burst
  3. GRB 260411B: SVOM/GRM observation of a long burst
  4. GRB 260409A: Insight-HXMT/HE detection
  5. GRB 260411B: Fermi GBM Detection
  6. GRB 260411B: GOTO optical counterpart candidate
  7. EP260409a: Gemini/FLAMINGOS2 J-band counterpart
  8. GRB 260411B: BALROG localization (Fermi Trigger 797587480 / GRB 260411337)
  9. GRB 260411B: Fermi GBM Final Real-time Localization
  10. GRB 260411A: Fermi GBM Final Real-time Localization
  11. GRB 260410A: COLIBRÍ optical upper limit
  12. EP-WXT01709259790: Optical Upper limits with kinder observations
  13. GRB 260410A: Fermi GBM Observation
  14. GRB 260410B: SVOM/GRM detection of a short faint burst
  15. The EP-WXT trigger 01709259790 is likely a flaring star
  16. GRB 260410B: Fermi GBM Final Real-time Localization
  17. EP-WXT01709259790: Xinglong optical upper limit
  18. GRB 260410A: Fermi-LAT detection
  19. GRB 260410A: Fermi GBM Final Real-time Localization
  20. EP260409a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  21. EP260321a: Chandra X-ray Non-detection
  22. GRB 260409A: Fermi GBM Final Real-time Localization
  23. GRB 260310A/AT2026fgk: Kilonova-Catcher SN peak identification
  24. The EP-WXT trigger 01709259773 is likely a flaring star
  25. GRB 260407A: GECAM-A detection
  26. GRB 260407A: Insight-HXMT/HE detection
  27. EP260409a: SVOM/VT optical upper limits
  28. EP260409a: COLIBRÍ optical upper limits
  29. GRB 260407A: CALET Gamma-Ray Burst Monitor detection
  30. EP260409a: Global MASTER-Net observations report
  31. EP260409a: Einstein Probe detection of an X-ray transient
  32. EP260321a: VLA radio detection
  33. GRB 260404A: Fermi GBM Final Localization
  34. GRB 260407A: Glowbug gamma-ray detection
  35. GRB 260402A: SVOM/ECLAIRs refined analysis
  36. GRB 260310A: Continued VLA Multi-frequency Radio Observations
  37. GRB 260310A / AT2026fgk: X-ray rebrightening
  38. EP260402a / GRB 260402A: Mephisto optical upper limits
  39. EP-WXT01709259586: Xinglong optical upper limit
  40. EP260403a: Mephisto optical upper limits
  41. EP260402a/GRB 260402A: Xinglong optical upper limit
  42. EP260321a: Upper limits from VLA radio observations
  43. GRID detection of GRB 260401A
  44. EP260321a: uGMRT observations
  45. GRB 260407A: Fermi GBM Final Real-time Localization
  46. EP260405a: GMOS-N optical upper limits
  47. EP260405a: SVOM/VT optical upper limits
  48. EP260405a: Global MASTER-Net observations report
  49. EP260405a: Einstein Probe detection of a fast X-ray transient
  50. The EP-WXT trigger 01709259621 is likely a flaring star
  51. EP260405.149 / EP-WXT 11900672904: COLIBRÍ optical upper limits
  52. The EP-WXT trigger 01709259615 is likely a flaring star
  53. Fermi trigger No 797039833: Global MASTER-Net observations report
  54. GRB 260403A: GECAM-B observation of a long burst
  55. EP260324A / AT 2026hir: COLIBRÍ further optical observations
  56. Fermi Gamma-ray Burst Monitor trigger 796972356/260404217 is not a GRB
  57. EP260403a: refined analysis of the EP-WXT and EP-FXT observations
  58. The EP-WXT trigger 01709259586 is likely a flaring star
  59. GRB 260330B: SVOM/VT further optical observation
  60. Fermi Gamma-ray Burst Monitor trigger 796931884/260403749 is not a GRB
  61. GRB 260330B: SVOM/ECLAIRs refined analysis
  62. EP260403a: LCO optical observations of the counterpart
  63. GRB 260310A/AT2026fgk: Kilonova-Catcher long term optical monitoring
  64. EP260403a: LCO optical counterpart detection
  65. EP260403a: COLIBRÍ optical counterpart candidate
  66. GRB 260330B: SVOM/VT optical candidate
  67. EP260403a: Einstein Probe detection of an X-ray transient
  68. GRB 260330B: EP-FXT follow-up and identification of candidate afterglow
  69. GRB 260403A: AstroSat CZTI detection
  70. EP260402a/GRB 260402A: refined analysis of the EP-WXT and EP-FXT observations
  71. GRB 260402B: GECAM-B observation
  72. EP260402a/GRB 260402A: Jinshan near-infrared upper limit
  73. GRB 260402C: NuSTAR detection of prompt emission
  74. GRB 260402C: AstroSat CZTI detection of a long burst
  75. EP260324A / AT 2026hir: COLIBRÍ optical observations
  76. GRB 260403A: Fermi GBM Final Real-time Localization
  77. EP260324A / AT 2026hir: Spectroscopic Observations with the Next Generation Palomar Spectrograph
  78. GRB 260402B: Fermi GBM Final Real-time Localization
  79. GRB 260402A: WINTER J-band upper limit
  80. GRB260402A: GROWTH-India Telescope optical upper limit
  81. GRB 260402A / EP260402a: SVOM/VT optical upper limits
  82. EP260402a/GRB 260402A: SVOM/C-GFT upper limit
  83. GRB 260401A: SVOM/GRM observation
  84. GRB 260401A: GECAM-B observation
  85. EP260402a/GRB 260402A: Einstein Probe detection of an X-ray transient
  86. GRB 260402A: Kilonova-Catcher optical upper limit
  87. GRB 260402A: MASTER optical observations
  88. GRB 260402A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  89. GRB 260402A: SVOM/MXT candidate X-ray afterglow
  90. GRB 260402A: SVOM detection of a burst
  91. Fermi GRB 260401A: Global MASTER-Net observations report
  92. GRB 260401A: Fermi GBM Observation
  93. GRB 260401A: NuSTAR detection of prompt emission
  94. GRB 260401A: CALET Gamma-Ray Burst Monitor detection
  95. GRB 260401A: MAXI/GSC detection
  96. GRB 260401A: BALROG localization (Fermi Trigger 796733611 / GRB 260401454)
  97. GRB 260401A: Fermi GBM Final Real-time Localization
  98. EP260329b: Mondy and Assy-Turgen optical upper limits
  99. GRB 260310A / AT2026fgk: Luminance-band optical follow-up with a 28cm telescope in Daocheng
  100. EP260321a :Xinglong optical observations

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