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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"

31729 results found.

  1. EP260321a: uGMRT observations
  2. EP260405a: GMOS-N optical upper limits
  3. EP260405a: SVOM/VT optical upper limits
  4. EP260405a: Global MASTER-Net observations report
  5. EP260405a: Einstein Probe detection of a fast X-ray transient
  6. GRB 260403A: GECAM-B observation of a long burst
  7. EP260324A / AT 2026hir: COLIBRÍ further optical observations
  8. EP260403a: refined analysis of the EP-WXT and EP-FXT observations
  9. GRB 260330B: SVOM/VT further optical observation
  10. GRB 260330B: SVOM/ECLAIRs refined analysis
  11. EP260403a: LCO optical observations of the counterpart
  12. GRB 260310A/AT2026fgk: Kilonova-Catcher long term optical monitoring
  13. EP260403a: LCO optical counterpart detection
  14. EP260403a: COLIBRÍ optical counterpart candidate
  15. GRB 260330B: SVOM/VT optical candidate
  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. EP260324A / AT 2026hir: COLIBRÍ optical observations
  23. EP260324A / AT 2026hir: Spectroscopic Observations with the Next Generation Palomar Spectrograph
  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. Fermi GRB 260401A: Global MASTER-Net observations report
  36. GRB 260401A: Fermi GBM Observation
  37. GRB 260401A: NuSTAR detection of prompt emission
  38. GRB 260401A: CALET Gamma-Ray Burst Monitor detection
  39. GRB 260401A: MAXI/GSC detection
  40. EP260329b: Mondy and Assy-Turgen optical upper limits
  41. GRB 260310A / AT2026fgk: Luminance-band optical follow-up with a 28cm telescope in Daocheng
  42. EP260321a :Xinglong optical observations
  43. EP260327a: Xinglong optical upper limit
  44. EP260329b: GOTO detection of optical counterpart
  45. GRB 260330B: SVOM/VT optical upper limits
  46. Konus-Wind detection of GRB 260320A
  47. Konus-Wind detection of GRB 260316B (duplicate submission)
  48. Konus-Wind detection of GRB 260316B
  49. GRB 260321A: SVOM/ECLAIRs refined analysis
  50. EP260329b: J-band upper limits with WINTER
  51. EP260329a: J-band upper limit with WINTER
  52. GRB 260330A: Glowbug gamma-ray detection
  53. GRB 260310A: VLA Multi-frequency Radio Observations
  54. Fermi GBM Sub-Threshold Detection of GRB 260330B
  55. GRB 260330B: LCO optical upper limits
  56. EP260324a / AT2026hir: g- and r-band optical follow-up with the PKU 60cm Telescope
  57. EP260329b: refined analysis of the EP-WXT and EP-FXT observations
  58. EP260329a: COLIBRÍ optical upper limit
  59. EP260329a: EP-FXT follow up observation
  60. EP260329a: NOT optical counterpart candidate
  61. EP260329b: Global MASTER-Net observations report
  62. GRB 260327A: Insight-HXMT/HE detection
  63. EP260329b: Optical follow-up with Kinder observations
  64. EP 260329b: COLIBRÍ optical observations
  65. EP260329a: Optical upper limit with Kinder observations
  66. EP260329b: LCO optical observations of the counterpart
  67. GRB 260326A: Insight-HXMT/HE detection
  68. EP260329b: Einstein Probe detection of an X-ray transient
  69. EP-WXT trigger 01709259209: TRT optical counterpart detection
  70. GRID detection of GRB 260326A
  71. GRB 260310A: Gemini-North Spectral Confirmation of Supernova Features
  72. EP260327a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  73. EP260327a: SVOM/VT optical upper limits
  74. SMA Detection of GRB 260310A / AT 2026fgk
  75. GRB 260307B: ATCA Radio Upper Limits
  76. EP260327a: WINTER J-band upper limit
  77. EP260327a: COLIBRÍ optical upper limits
  78. EP260327a: Gemini-North optical upper limits
  79. EP260324a: GROWTH-India Telescope optical observation
  80. EP260327a: Global MASTER-Net observations report
  81. GRB 260310A / AT 2026fgk: COLIBRÍ photometric evidence of the emerging supernova
  82. GRB 260310A: OSIRIS+/GTC spectroscopic detection of the associated BL-Ic, SN 2026fgk
  83. GRB 260310A / AT2026fgk: Late-time infrared detection with MIRAGE on the MDM 1.3m telescope
  84. IPN triangulation of GRB 260320A
  85. GRB 260310A / AT2026fgk: R- and I-band observations with the PKU 60 cm optical telescope
  86. GRB 260326A: Fermi GBM Detection
  87. EP260321a: JinShan near-infrared observations
  88. EP260321a: Upper limits from a neutrino search with IceCube
  89. GRB 260310A/AT2026fgk: Kilonova-Catcher late optical afterglow detection at about 15 days post trigger time
  90. IPN triangulation of GRB 260316B
  91. EP260321a: J-band observations by the SYSU 80 cm infrared telescope
  92. GRID detection of GRB 260320A
  93. EP260321a: Gemini-South confirmation of a supernova (duplicate submission)
  94. EP260321a: Gemini-South confirmation of a supernova
  95. EP260321a: VLT/FORS2 spectroscopy confirmation of an associated type Ic-BL supernova SN 2026gzf
  96. GRB 260310A: LBT optical observations
  97. EP260321A: Mondy optical observations
  98. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limits at the FXT positions
  99. EP-WXT trigger 01709259112: confirmation of a stellar flare by BOOTES-5 & BOOTES-7
  100. GRB 260316B: CALET Gamma-Ray Burst Monitor detection

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