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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 260402C: AstroSat CZTI detection of a long burst
  2. EP260324A / AT 2026hir: COLIBRÍ optical observations
  3. GRB 260403A: Fermi GBM Final Real-time Localization
  4. EP260324A / AT 2026hir: Spectroscopic Observations with the Next Generation Palomar Spectrograph
  5. GRB 260402B: Fermi GBM Final Real-time Localization
  6. GRB 260402A: WINTER J-band upper limit
  7. GRB260402A: GROWTH-India Telescope optical upper limit
  8. GRB 260402A / EP260402a: SVOM/VT optical upper limits
  9. EP260402a/GRB 260402A: SVOM/C-GFT upper limit
  10. GRB 260401A: SVOM/GRM observation
  11. GRB 260401A: GECAM-B observation
  12. EP260402a/GRB 260402A: Einstein Probe detection of an X-ray transient
  13. GRB 260402A: Kilonova-Catcher optical upper limit
  14. GRB 260402A: MASTER optical observations
  15. GRB 260402A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  16. GRB 260402A: SVOM/MXT candidate X-ray afterglow
  17. GRB 260402A: SVOM detection of a burst
  18. Fermi GRB 260401A: Global MASTER-Net observations report
  19. GRB 260401A: Fermi GBM Observation
  20. GRB 260401A: NuSTAR detection of prompt emission
  21. GRB 260401A: CALET Gamma-Ray Burst Monitor detection
  22. GRB 260401A: MAXI/GSC detection
  23. GRB 260401A: BALROG localization (Fermi Trigger 796733611 / GRB 260401454)
  24. GRB 260401A: Fermi GBM Final Real-time Localization
  25. EP260329b: Mondy and Assy-Turgen optical upper limits
  26. GRB 260310A / AT2026fgk: Luminance-band optical follow-up with a 28cm telescope in Daocheng
  27. EP260321a :Xinglong optical observations
  28. EP260327a: Xinglong optical upper limit
  29. EP260329b: GOTO detection of optical counterpart
  30. GRB 260330B: SVOM/VT optical upper limits
  31. Konus-Wind detection of GRB 260320A
  32. Konus-Wind detection of GRB 260316B (duplicate submission)
  33. Konus-Wind detection of GRB 260316B
  34. GRB 260321A: SVOM/ECLAIRs refined analysis
  35. EP260329b: J-band upper limits with WINTER
  36. EP260329a: J-band upper limit with WINTER
  37. GRB 260330A: Glowbug gamma-ray detection
  38. GRB 260310A: VLA Multi-frequency Radio Observations
  39. Fermi GBM Sub-Threshold Detection of GRB 260330B
  40. GRB 260330B: LCO optical upper limits
  41. GRB 260330B: SVOM detection of a burst
  42. EP260324a / AT2026hir: g- and r-band optical follow-up with the PKU 60cm Telescope
  43. EP260329b: refined analysis of the EP-WXT and EP-FXT observations
  44. EP260329a: COLIBRÍ optical upper limit
  45. EP260329a: EP-FXT follow up observation
  46. EP260329a: NOT optical counterpart candidate
  47. GRB 260330A: Fermi GBM Final Real-time Localization
  48. EP260329b: Global MASTER-Net observations report
  49. Fermi trigger No 796485221: Global MASTER-Net observations report
  50. GRB 260327A: Insight-HXMT/HE detection
  51. EP260329b: Optical follow-up with Kinder observations
  52. EP 260329b: COLIBRÍ optical observations
  53. EP260329a: Optical upper limit with Kinder observations
  54. EP260329b: LCO optical observations of the counterpart
  55. GRB 260326A: Insight-HXMT/HE detection
  56. EP260329b: Einstein Probe detection of an X-ray transient
  57. EP260329a: Einstein Probe detection of an X-ray transient
  58. EP-WXT trigger 01709259209: TRT optical counterpart detection
  59. The EP-WXT trigger 01709259209 (EP260329b?): Las Cumbres discovery of the optical counterpart
  60. GRID detection of GRB 260326A
  61. GRB 260310A: Gemini-North Spectral Confirmation of Supernova Features
  62. EP260327a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  63. EP260327a: SVOM/VT optical upper limits
  64. SMA Detection of GRB 260310A / AT 2026fgk
  65. GRB 260307B: ATCA Radio Upper Limits
  66. EP260327a: WINTER J-band upper limit
  67. EP260327a: COLIBRÍ optical upper limits
  68. GRB 260327A: AstroSat CZTI detection of a long burst
  69. EP260327a: Gemini-North optical upper limits
  70. EP260324a: GROWTH-India Telescope optical observation
  71. EP260327a: Global MASTER-Net observations report
  72. EP260327a: Einstein Probe detection of an X-ray transient
  73. GRB 260310A / AT 2026fgk: COLIBRÍ photometric evidence of the emerging supernova
  74. GRB 260310A: OSIRIS+/GTC spectroscopic detection of the associated BL-Ic, SN 2026fgk
  75. The EP-WXT trigger 01709259173 is likely a flaring star
  76. GRB 260310A / AT2026fgk: Late-time infrared detection with MIRAGE on the MDM 1.3m telescope
  77. IPN triangulation of GRB 260320A
  78. EP260324a: ZTF discovery of the optical counterpart ZTF26aapviim/AT2026hir
  79. GRB 260310A / AT2026fgk: R- and I-band observations with the PKU 60 cm optical telescope
  80. GRB 260326A: Fermi GBM Detection
  81. EP260321a: JinShan near-infrared observations
  82. GRB 260325A: Fermi GBM Final Localization
  83. GRB 260326A: Fermi GBM Final Real-time Localization
  84. EP260321a: Upper limits from a neutrino search with IceCube
  85. Fermi Gamma-ray Burst Monitor trigger 796145512/260325647 is not a GRB
  86. GRB 260310A/AT2026fgk: Kilonova-Catcher late optical afterglow detection at about 15 days post trigger time
  87. IPN triangulation of GRB 260316B
  88. EP260321a: J-band observations by the SYSU 80 cm infrared telescope
  89. GRID detection of GRB 260320A
  90. EP260321a: Gemini-South confirmation of a supernova (duplicate submission)
  91. EP260321a: Gemini-South confirmation of a supernova
  92. Fermi Gamma-ray Burst Monitor trigger 796060650/260324665 is not a GRB
  93. EP260321a: VLT/FORS2 spectroscopy confirmation of an associated type Ic-BL supernova SN 2026gzf
  94. GRB 260310A: LBT optical observations
  95. EP260321A: Mondy optical observations
  96. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limits at the FXT positions
  97. EP-WXT trigger 01709259112: confirmation of a stellar flare by BOOTES-5 & BOOTES-7
  98. GRB 260316B: CALET Gamma-Ray Burst Monitor detection
  99. The EP-WXT trigger 01709259112 is likely a flaring star
  100. Fermi GRB 260323A: Global MASTER-Net observations report

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