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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 260330B: SVOM/ECLAIRs refined analysis
  2. EP260403a: LCO optical observations of the counterpart
  3. GRB 260310A/AT2026fgk: Kilonova-Catcher long term optical monitoring
  4. EP260403a: LCO optical counterpart detection
  5. EP260403a: COLIBRÍ optical counterpart candidate
  6. GRB 260330B: SVOM/VT optical candidate
  7. EP260403a: Einstein Probe detection of an X-ray transient
  8. GRB 260330B: EP-FXT follow-up and identification of candidate afterglow
  9. GRB 260403A: AstroSat CZTI detection
  10. EP260402a/GRB 260402A: refined analysis of the EP-WXT and EP-FXT observations
  11. GRB 260402B: GECAM-B observation
  12. EP260402a/GRB 260402A: Jinshan near-infrared upper limit
  13. GRB 260402C: NuSTAR detection of prompt emission
  14. GRB 260402C: AstroSat CZTI detection of a long burst
  15. EP260324A / AT 2026hir: COLIBRÍ optical observations
  16. GRB 260403A: Fermi GBM Final Real-time Localization
  17. EP260324A / AT 2026hir: Spectroscopic Observations with the Next Generation Palomar Spectrograph
  18. GRB 260402B: Fermi GBM Final Real-time Localization
  19. GRB 260402A: WINTER J-band upper limit
  20. GRB260402A: GROWTH-India Telescope optical upper limit
  21. GRB 260402A / EP260402a: SVOM/VT optical upper limits
  22. EP260402a/GRB 260402A: SVOM/C-GFT upper limit
  23. GRB 260401A: SVOM/GRM observation
  24. GRB 260401A: GECAM-B observation
  25. EP260402a/GRB 260402A: Einstein Probe detection of an X-ray transient
  26. GRB 260402A: Kilonova-Catcher optical upper limit
  27. GRB 260402A: MASTER optical observations
  28. GRB 260402A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  29. GRB 260402A: SVOM/MXT candidate X-ray afterglow
  30. GRB 260402A: SVOM detection of a burst
  31. Fermi GRB 260401A: Global MASTER-Net observations report
  32. GRB 260401A: Fermi GBM Observation
  33. GRB 260401A: NuSTAR detection of prompt emission
  34. GRB 260401A: CALET Gamma-Ray Burst Monitor detection
  35. GRB 260401A: MAXI/GSC detection
  36. GRB 260401A: BALROG localization (Fermi Trigger 796733611 / GRB 260401454)
  37. GRB 260401A: Fermi GBM Final Real-time Localization
  38. EP260329b: Mondy and Assy-Turgen optical upper limits
  39. GRB 260310A / AT2026fgk: Luminance-band optical follow-up with a 28cm telescope in Daocheng
  40. EP260321a :Xinglong optical observations
  41. EP260327a: Xinglong optical upper limit
  42. EP260329b: GOTO detection of optical counterpart
  43. GRB 260330B: SVOM/VT optical upper limits
  44. Konus-Wind detection of GRB 260320A
  45. Konus-Wind detection of GRB 260316B (duplicate submission)
  46. Konus-Wind detection of GRB 260316B
  47. GRB 260321A: SVOM/ECLAIRs refined analysis
  48. EP260329b: J-band upper limits with WINTER
  49. EP260329a: J-band upper limit with WINTER
  50. GRB 260330A: Glowbug gamma-ray detection
  51. GRB 260310A: VLA Multi-frequency Radio Observations
  52. Fermi GBM Sub-Threshold Detection of GRB 260330B
  53. GRB 260330B: LCO optical upper limits
  54. GRB 260330B: SVOM detection of a burst
  55. EP260324a / AT2026hir: g- and r-band optical follow-up with the PKU 60cm Telescope
  56. EP260329b: refined analysis of the EP-WXT and EP-FXT observations
  57. EP260329a: COLIBRÍ optical upper limit
  58. EP260329a: EP-FXT follow up observation
  59. EP260329a: NOT optical counterpart candidate
  60. GRB 260330A: Fermi GBM Final Real-time Localization
  61. EP260329b: Global MASTER-Net observations report
  62. Fermi trigger No 796485221: Global MASTER-Net observations report
  63. GRB 260327A: Insight-HXMT/HE detection
  64. EP260329b: Optical follow-up with Kinder observations
  65. EP 260329b: COLIBRÍ optical observations
  66. EP260329a: Optical upper limit with Kinder observations
  67. EP260329b: LCO optical observations of the counterpart
  68. GRB 260326A: Insight-HXMT/HE detection
  69. EP260329b: Einstein Probe detection of an X-ray transient
  70. EP260329a: Einstein Probe detection of an X-ray transient
  71. EP-WXT trigger 01709259209: TRT optical counterpart detection
  72. The EP-WXT trigger 01709259209 (EP260329b?): Las Cumbres discovery of the optical counterpart
  73. GRID detection of GRB 260326A
  74. GRB 260310A: Gemini-North Spectral Confirmation of Supernova Features
  75. EP260327a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  76. EP260327a: SVOM/VT optical upper limits
  77. SMA Detection of GRB 260310A / AT 2026fgk
  78. GRB 260307B: ATCA Radio Upper Limits
  79. EP260327a: WINTER J-band upper limit
  80. EP260327a: COLIBRÍ optical upper limits
  81. GRB 260327A: AstroSat CZTI detection of a long burst
  82. EP260327a: Gemini-North optical upper limits
  83. EP260324a: GROWTH-India Telescope optical observation
  84. EP260327a: Global MASTER-Net observations report
  85. EP260327a: Einstein Probe detection of an X-ray transient
  86. GRB 260310A / AT 2026fgk: COLIBRÍ photometric evidence of the emerging supernova
  87. GRB 260310A: OSIRIS+/GTC spectroscopic detection of the associated BL-Ic, SN 2026fgk
  88. The EP-WXT trigger 01709259173 is likely a flaring star
  89. GRB 260310A / AT2026fgk: Late-time infrared detection with MIRAGE on the MDM 1.3m telescope
  90. IPN triangulation of GRB 260320A
  91. EP260324a: ZTF discovery of the optical counterpart ZTF26aapviim/AT2026hir
  92. GRB 260310A / AT2026fgk: R- and I-band observations with the PKU 60 cm optical telescope
  93. GRB 260326A: Fermi GBM Detection
  94. EP260321a: JinShan near-infrared observations
  95. GRB 260325A: Fermi GBM Final Localization
  96. GRB 260326A: Fermi GBM Final Real-time Localization
  97. EP260321a: Upper limits from a neutrino search with IceCube
  98. Fermi Gamma-ray Burst Monitor trigger 796145512/260325647 is not a GRB
  99. GRB 260310A/AT2026fgk: Kilonova-Catcher late optical afterglow detection at about 15 days post trigger time
  100. IPN triangulation of GRB 260316B

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