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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. Fermi Gamma-ray Burst Monitor trigger 796972356/260404217 is not a GRB
  2. EP260403a: refined analysis of the EP-WXT and EP-FXT observations
  3. The EP-WXT trigger 01709259586 is likely a flaring star
  4. GRB 260330B: SVOM/VT further optical observation
  5. Fermi Gamma-ray Burst Monitor trigger 796931884/260403749 is not a GRB
  6. GRB 260330B: SVOM/ECLAIRs refined analysis
  7. EP260403a: LCO optical observations of the counterpart
  8. GRB 260310A/AT2026fgk: Kilonova-Catcher long term optical monitoring
  9. EP260403a: LCO optical counterpart detection
  10. EP260403a: COLIBRÍ optical counterpart candidate
  11. GRB 260330B: SVOM/VT optical candidate
  12. EP260403a: Einstein Probe detection of an X-ray transient
  13. GRB 260330B: EP-FXT follow-up and identification of candidate afterglow
  14. GRB 260403A: AstroSat CZTI detection
  15. EP260402a/GRB 260402A: refined analysis of the EP-WXT and EP-FXT observations
  16. GRB 260402B: GECAM-B observation
  17. EP260402a/GRB 260402A: Jinshan near-infrared upper limit
  18. GRB 260402C: NuSTAR detection of prompt emission
  19. GRB 260402C: AstroSat CZTI detection of a long burst
  20. EP260324A / AT 2026hir: COLIBRÍ optical observations
  21. GRB 260403A: Fermi GBM Final Real-time Localization
  22. EP260324A / AT 2026hir: Spectroscopic Observations with the Next Generation Palomar Spectrograph
  23. GRB 260402B: Fermi GBM Final Real-time Localization
  24. GRB 260402A: WINTER J-band upper limit
  25. GRB260402A: GROWTH-India Telescope optical upper limit
  26. GRB 260402A / EP260402a: SVOM/VT optical upper limits
  27. EP260402a/GRB 260402A: SVOM/C-GFT upper limit
  28. GRB 260401A: SVOM/GRM observation
  29. GRB 260401A: GECAM-B observation
  30. EP260402a/GRB 260402A: Einstein Probe detection of an X-ray transient
  31. GRB 260402A: Kilonova-Catcher optical upper limit
  32. GRB 260402A: MASTER optical observations
  33. GRB 260402A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  34. GRB 260402A: SVOM/MXT candidate X-ray afterglow
  35. GRB 260402A: SVOM detection of a burst
  36. Fermi GRB 260401A: Global MASTER-Net observations report
  37. GRB 260401A: Fermi GBM Observation
  38. GRB 260401A: NuSTAR detection of prompt emission
  39. GRB 260401A: CALET Gamma-Ray Burst Monitor detection
  40. GRB 260401A: MAXI/GSC detection
  41. GRB 260401A: BALROG localization (Fermi Trigger 796733611 / GRB 260401454)
  42. GRB 260401A: Fermi GBM Final Real-time Localization
  43. EP260329b: Mondy and Assy-Turgen optical upper limits
  44. GRB 260310A / AT2026fgk: Luminance-band optical follow-up with a 28cm telescope in Daocheng
  45. EP260321a :Xinglong optical observations
  46. EP260327a: Xinglong optical upper limit
  47. EP260329b: GOTO detection of optical counterpart
  48. GRB 260330B: SVOM/VT optical upper limits
  49. Konus-Wind detection of GRB 260320A
  50. Konus-Wind detection of GRB 260316B (duplicate submission)
  51. Konus-Wind detection of GRB 260316B
  52. GRB 260321A: SVOM/ECLAIRs refined analysis
  53. EP260329b: J-band upper limits with WINTER
  54. EP260329a: J-band upper limit with WINTER
  55. GRB 260330A: Glowbug gamma-ray detection
  56. GRB 260310A: VLA Multi-frequency Radio Observations
  57. Fermi GBM Sub-Threshold Detection of GRB 260330B
  58. GRB 260330B: LCO optical upper limits
  59. GRB 260330B: SVOM detection of a burst
  60. EP260324a / AT2026hir: g- and r-band optical follow-up with the PKU 60cm Telescope
  61. EP260329b: refined analysis of the EP-WXT and EP-FXT observations
  62. EP260329a: COLIBRÍ optical upper limit
  63. EP260329a: EP-FXT follow up observation
  64. EP260329a: NOT optical counterpart candidate
  65. GRB 260330A: Fermi GBM Final Real-time Localization
  66. EP260329b: Global MASTER-Net observations report
  67. Fermi trigger No 796485221: Global MASTER-Net observations report
  68. GRB 260327A: Insight-HXMT/HE detection
  69. EP260329b: Optical follow-up with Kinder observations
  70. EP 260329b: COLIBRÍ optical observations
  71. EP260329a: Optical upper limit with Kinder observations
  72. EP260329b: LCO optical observations of the counterpart
  73. GRB 260326A: Insight-HXMT/HE detection
  74. EP260329b: Einstein Probe detection of an X-ray transient
  75. EP260329a: Einstein Probe detection of an X-ray transient
  76. EP-WXT trigger 01709259209: TRT optical counterpart detection
  77. The EP-WXT trigger 01709259209 (EP260329b?): Las Cumbres discovery of the optical counterpart
  78. GRID detection of GRB 260326A
  79. GRB 260310A: Gemini-North Spectral Confirmation of Supernova Features
  80. EP260327a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  81. EP260327a: SVOM/VT optical upper limits
  82. SMA Detection of GRB 260310A / AT 2026fgk
  83. GRB 260307B: ATCA Radio Upper Limits
  84. EP260327a: WINTER J-band upper limit
  85. EP260327a: COLIBRÍ optical upper limits
  86. GRB 260327A: AstroSat CZTI detection of a long burst
  87. EP260327a: Gemini-North optical upper limits
  88. EP260324a: GROWTH-India Telescope optical observation
  89. EP260327a: Global MASTER-Net observations report
  90. EP260327a: Einstein Probe detection of an X-ray transient
  91. GRB 260310A / AT 2026fgk: COLIBRÍ photometric evidence of the emerging supernova
  92. GRB 260310A: OSIRIS+/GTC spectroscopic detection of the associated BL-Ic, SN 2026fgk
  93. The EP-WXT trigger 01709259173 is likely a flaring star
  94. GRB 260310A / AT2026fgk: Late-time infrared detection with MIRAGE on the MDM 1.3m telescope
  95. IPN triangulation of GRB 260320A
  96. EP260324a: ZTF discovery of the optical counterpart ZTF26aapviim/AT2026hir
  97. GRB 260310A / AT2026fgk: R- and I-band observations with the PKU 60 cm optical telescope
  98. GRB 260326A: Fermi GBM Detection
  99. EP260321a: JinShan near-infrared observations
  100. GRB 260325A: Fermi GBM Final Localization

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