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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 trigger No 797039833: Global MASTER-Net observations report
  2. GRB 260403A: GECAM-B observation of a long burst
  3. EP260324A / AT 2026hir: COLIBRÍ further optical observations
  4. Fermi Gamma-ray Burst Monitor trigger 796972356/260404217 is not a GRB
  5. EP260403a: refined analysis of the EP-WXT and EP-FXT observations
  6. The EP-WXT trigger 01709259586 is likely a flaring star
  7. GRB 260330B: SVOM/VT further optical observation
  8. Fermi Gamma-ray Burst Monitor trigger 796931884/260403749 is not a GRB
  9. GRB 260330B: SVOM/ECLAIRs refined analysis
  10. EP260403a: LCO optical observations of the counterpart
  11. GRB 260310A/AT2026fgk: Kilonova-Catcher long term optical monitoring
  12. EP260403a: LCO optical counterpart detection
  13. EP260403a: COLIBRÍ optical counterpart candidate
  14. GRB 260330B: SVOM/VT optical candidate
  15. EP260403a: Einstein Probe detection of an X-ray transient
  16. GRB 260330B: EP-FXT follow-up and identification of candidate afterglow
  17. GRB 260403A: AstroSat CZTI detection
  18. EP260402a/GRB 260402A: refined analysis of the EP-WXT and EP-FXT observations
  19. GRB 260402B: GECAM-B observation
  20. EP260402a/GRB 260402A: Jinshan near-infrared upper limit
  21. GRB 260402C: NuSTAR detection of prompt emission
  22. GRB 260402C: AstroSat CZTI detection of a long burst
  23. EP260324A / AT 2026hir: COLIBRÍ optical observations
  24. GRB 260403A: Fermi GBM Final Real-time Localization
  25. EP260324A / AT 2026hir: Spectroscopic Observations with the Next Generation Palomar Spectrograph
  26. GRB 260402B: Fermi GBM Final Real-time Localization
  27. GRB 260402A: WINTER J-band upper limit
  28. GRB260402A: GROWTH-India Telescope optical upper limit
  29. GRB 260402A / EP260402a: SVOM/VT optical upper limits
  30. EP260402a/GRB 260402A: SVOM/C-GFT upper limit
  31. GRB 260401A: SVOM/GRM observation
  32. GRB 260401A: GECAM-B observation
  33. EP260402a/GRB 260402A: Einstein Probe detection of an X-ray transient
  34. GRB 260402A: Kilonova-Catcher optical upper limit
  35. GRB 260402A: MASTER optical observations
  36. GRB 260402A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  37. GRB 260402A: SVOM/MXT candidate X-ray afterglow
  38. GRB 260402A: SVOM detection of a burst
  39. Fermi GRB 260401A: Global MASTER-Net observations report
  40. GRB 260401A: Fermi GBM Observation
  41. GRB 260401A: NuSTAR detection of prompt emission
  42. GRB 260401A: CALET Gamma-Ray Burst Monitor detection
  43. GRB 260401A: MAXI/GSC detection
  44. GRB 260401A: BALROG localization (Fermi Trigger 796733611 / GRB 260401454)
  45. GRB 260401A: Fermi GBM Final Real-time Localization
  46. EP260329b: Mondy and Assy-Turgen optical upper limits
  47. GRB 260310A / AT2026fgk: Luminance-band optical follow-up with a 28cm telescope in Daocheng
  48. EP260321a :Xinglong optical observations
  49. EP260327a: Xinglong optical upper limit
  50. EP260329b: GOTO detection of optical counterpart
  51. GRB 260330B: SVOM/VT optical upper limits
  52. Konus-Wind detection of GRB 260320A
  53. Konus-Wind detection of GRB 260316B (duplicate submission)
  54. Konus-Wind detection of GRB 260316B
  55. GRB 260321A: SVOM/ECLAIRs refined analysis
  56. EP260329b: J-band upper limits with WINTER
  57. EP260329a: J-band upper limit with WINTER
  58. GRB 260330A: Glowbug gamma-ray detection
  59. GRB 260310A: VLA Multi-frequency Radio Observations
  60. Fermi GBM Sub-Threshold Detection of GRB 260330B
  61. GRB 260330B: LCO optical upper limits
  62. GRB 260330B: SVOM detection of a burst
  63. EP260324a / AT2026hir: g- and r-band optical follow-up with the PKU 60cm Telescope
  64. EP260329b: refined analysis of the EP-WXT and EP-FXT observations
  65. EP260329a: COLIBRÍ optical upper limit
  66. EP260329a: EP-FXT follow up observation
  67. EP260329a: NOT optical counterpart candidate
  68. GRB 260330A: Fermi GBM Final Real-time Localization
  69. EP260329b: Global MASTER-Net observations report
  70. Fermi trigger No 796485221: Global MASTER-Net observations report
  71. GRB 260327A: Insight-HXMT/HE detection
  72. EP260329b: Optical follow-up with Kinder observations
  73. EP 260329b: COLIBRÍ optical observations
  74. EP260329a: Optical upper limit with Kinder observations
  75. EP260329b: LCO optical observations of the counterpart
  76. GRB 260326A: Insight-HXMT/HE detection
  77. EP260329b: Einstein Probe detection of an X-ray transient
  78. EP260329a: Einstein Probe detection of an X-ray transient
  79. EP-WXT trigger 01709259209: TRT optical counterpart detection
  80. The EP-WXT trigger 01709259209 (EP260329b?): Las Cumbres discovery of the optical counterpart
  81. GRID detection of GRB 260326A
  82. GRB 260310A: Gemini-North Spectral Confirmation of Supernova Features
  83. EP260327a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  84. EP260327a: SVOM/VT optical upper limits
  85. SMA Detection of GRB 260310A / AT 2026fgk
  86. GRB 260307B: ATCA Radio Upper Limits
  87. EP260327a: WINTER J-band upper limit
  88. EP260327a: COLIBRÍ optical upper limits
  89. GRB 260327A: AstroSat CZTI detection of a long burst
  90. EP260327a: Gemini-North optical upper limits
  91. EP260324a: GROWTH-India Telescope optical observation
  92. EP260327a: Global MASTER-Net observations report
  93. EP260327a: Einstein Probe detection of an X-ray transient
  94. GRB 260310A / AT 2026fgk: COLIBRÍ photometric evidence of the emerging supernova
  95. GRB 260310A: OSIRIS+/GTC spectroscopic detection of the associated BL-Ic, SN 2026fgk
  96. The EP-WXT trigger 01709259173 is likely a flaring star
  97. GRB 260310A / AT2026fgk: Late-time infrared detection with MIRAGE on the MDM 1.3m telescope
  98. IPN triangulation of GRB 260320A
  99. EP260324a: ZTF discovery of the optical counterpart ZTF26aapviim/AT2026hir
  100. GRB 260310A / AT2026fgk: R- and I-band observations with the PKU 60 cm optical telescope

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