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

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