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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 260401A: GECAM-B observation
  2. EP260402a/GRB 260402A: Einstein Probe detection of an X-ray transient
  3. GRB 260402A: Kilonova-Catcher optical upper limit
  4. GRB 260402A: MASTER optical observations
  5. GRB 260402A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  6. GRB 260402A: SVOM/MXT candidate X-ray afterglow
  7. GRB 260402A: SVOM detection of a burst
  8. Fermi GRB 260401A: Global MASTER-Net observations report
  9. GRB 260401A: Fermi GBM Observation
  10. GRB 260401A: NuSTAR detection of prompt emission
  11. GRB 260401A: CALET Gamma-Ray Burst Monitor detection
  12. GRB 260401A: MAXI/GSC detection
  13. GRB 260401A: BALROG localization (Fermi Trigger 796733611 / GRB 260401454)
  14. GRB 260401A: Fermi GBM Final Real-time Localization
  15. EP260329b: Mondy and Assy-Turgen optical upper limits
  16. GRB 260310A / AT2026fgk: Luminance-band optical follow-up with a 28cm telescope in Daocheng
  17. EP260321a :Xinglong optical observations
  18. EP260327a: Xinglong optical upper limit
  19. EP260329b: GOTO detection of optical counterpart
  20. GRB 260330B: SVOM/VT optical upper limits
  21. Konus-Wind detection of GRB 260320A
  22. Konus-Wind detection of GRB 260316B (duplicate submission)
  23. Konus-Wind detection of GRB 260316B
  24. GRB 260321A: SVOM/ECLAIRs refined analysis
  25. EP260329b: J-band upper limits with WINTER
  26. EP260329a: J-band upper limit with WINTER
  27. GRB 260330A: Glowbug gamma-ray detection
  28. GRB 260310A: VLA Multi-frequency Radio Observations
  29. Fermi GBM Sub-Threshold Detection of GRB 260330B
  30. GRB 260330B: LCO optical upper limits
  31. GRB 260330B: SVOM detection of a burst
  32. EP260324a / AT2026hir: g- and r-band optical follow-up with the PKU 60cm Telescope
  33. EP260329b: refined analysis of the EP-WXT and EP-FXT observations
  34. EP260329a: COLIBRÍ optical upper limit
  35. EP260329a: EP-FXT follow up observation
  36. EP260329a: NOT optical counterpart candidate
  37. GRB 260330A: Fermi GBM Final Real-time Localization
  38. EP260329b: Global MASTER-Net observations report
  39. Fermi trigger No 796485221: Global MASTER-Net observations report
  40. GRB 260327A: Insight-HXMT/HE detection
  41. EP260329b: Optical follow-up with Kinder observations
  42. EP 260329b: COLIBRÍ optical observations
  43. EP260329a: Optical upper limit with Kinder observations
  44. EP260329b: LCO optical observations of the counterpart
  45. GRB 260326A: Insight-HXMT/HE detection
  46. EP260329b: Einstein Probe detection of an X-ray transient
  47. EP260329a: Einstein Probe detection of an X-ray transient
  48. EP-WXT trigger 01709259209: TRT optical counterpart detection
  49. The EP-WXT trigger 01709259209 (EP260329b?): Las Cumbres discovery of the optical counterpart
  50. GRID detection of GRB 260326A
  51. GRB 260310A: Gemini-North Spectral Confirmation of Supernova Features
  52. EP260327a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  53. EP260327a: SVOM/VT optical upper limits
  54. SMA Detection of GRB 260310A / AT 2026fgk
  55. GRB 260307B: ATCA Radio Upper Limits
  56. EP260327a: WINTER J-band upper limit
  57. EP260327a: COLIBRÍ optical upper limits
  58. GRB 260327A: AstroSat CZTI detection of a long burst
  59. EP260327a: Gemini-North optical upper limits
  60. EP260324a: GROWTH-India Telescope optical observation
  61. EP260327a: Global MASTER-Net observations report
  62. EP260327a: Einstein Probe detection of an X-ray transient
  63. GRB 260310A / AT 2026fgk: COLIBRÍ photometric evidence of the emerging supernova
  64. GRB 260310A: OSIRIS+/GTC spectroscopic detection of the associated BL-Ic, SN 2026fgk
  65. The EP-WXT trigger 01709259173 is likely a flaring star
  66. GRB 260310A / AT2026fgk: Late-time infrared detection with MIRAGE on the MDM 1.3m telescope
  67. IPN triangulation of GRB 260320A
  68. EP260324a: ZTF discovery of the optical counterpart ZTF26aapviim/AT2026hir
  69. GRB 260310A / AT2026fgk: R- and I-band observations with the PKU 60 cm optical telescope
  70. GRB 260326A: Fermi GBM Detection
  71. EP260321a: JinShan near-infrared observations
  72. GRB 260325A: Fermi GBM Final Localization
  73. GRB 260326A: Fermi GBM Final Real-time Localization
  74. EP260321a: Upper limits from a neutrino search with IceCube
  75. Fermi Gamma-ray Burst Monitor trigger 796145512/260325647 is not a GRB
  76. GRB 260310A/AT2026fgk: Kilonova-Catcher late optical afterglow detection at about 15 days post trigger time
  77. IPN triangulation of GRB 260316B
  78. EP260321a: J-band observations by the SYSU 80 cm infrared telescope
  79. GRID detection of GRB 260320A
  80. EP260321a: Gemini-South confirmation of a supernova (duplicate submission)
  81. EP260321a: Gemini-South confirmation of a supernova
  82. Fermi Gamma-ray Burst Monitor trigger 796060650/260324665 is not a GRB
  83. EP260321a: VLT/FORS2 spectroscopy confirmation of an associated type Ic-BL supernova SN 2026gzf
  84. GRB 260310A: LBT optical observations
  85. EP260321A: Mondy optical observations
  86. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limits at the FXT positions
  87. EP-WXT trigger 01709259112: confirmation of a stellar flare by BOOTES-5 & BOOTES-7
  88. GRB 260316B: CALET Gamma-Ray Burst Monitor detection
  89. The EP-WXT trigger 01709259112 is likely a flaring star
  90. Fermi GRB 260323A: Global MASTER-Net observations report
  91. GRB 260323A: Fermi GBM Final Real-time Localization
  92. GRB260310A: Palomar 60-inch photometry of an extremely bright late-time afterglow with a temporal break at 8 days
  93. GRB 260310A/AT2026fgk: Detection of temporal steepening in Einstein Probe X-ray data
  94. GRB 260322A: Fermi GBM Final Localization
  95. GRB 260320A: Glowbug gamma-ray detection
  96. EP260321a / AT2026gzf: VLT/X-shooter detection of supernova-like spectral features at z = 0.0344
  97. EP260321a: COLIBRÍ further optical observations and brightening
  98. Fermi Gamma-ray Burst Monitor trigger 795918973/260323025 is not a GRB
  99. EP260321a: Continued brightening from Kinder follow-up of the emerging supernova candidate
  100. EP260214b: ATCA 6 GHz detection

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