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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 260402A: SVOM detection of a burst
  2. Fermi GRB 260401A: Global MASTER-Net observations report
  3. GRB 260401A: Fermi GBM Observation
  4. GRB 260401A: NuSTAR detection of prompt emission
  5. GRB 260401A: CALET Gamma-Ray Burst Monitor detection
  6. GRB 260401A: MAXI/GSC detection
  7. GRB 260401A: BALROG localization (Fermi Trigger 796733611 / GRB 260401454)
  8. GRB 260401A: Fermi GBM Final Real-time Localization
  9. EP260329b: Mondy and Assy-Turgen optical upper limits
  10. GRB 260310A / AT2026fgk: Luminance-band optical follow-up with a 28cm telescope in Daocheng
  11. EP260321a :Xinglong optical observations
  12. EP260327a: Xinglong optical upper limit
  13. EP260329b: GOTO detection of optical counterpart
  14. GRB 260330B: SVOM/VT optical upper limits
  15. Konus-Wind detection of GRB 260320A
  16. Konus-Wind detection of GRB 260316B (duplicate submission)
  17. Konus-Wind detection of GRB 260316B
  18. GRB 260321A: SVOM/ECLAIRs refined analysis
  19. EP260329b: J-band upper limits with WINTER
  20. EP260329a: J-band upper limit with WINTER
  21. GRB 260330A: Glowbug gamma-ray detection
  22. GRB 260310A: VLA Multi-frequency Radio Observations
  23. Fermi GBM Sub-Threshold Detection of GRB 260330B
  24. GRB 260330B: LCO optical upper limits
  25. GRB 260330B: SVOM detection of a burst
  26. EP260324a / AT2026hir: g- and r-band optical follow-up with the PKU 60cm Telescope
  27. EP260329b: refined analysis of the EP-WXT and EP-FXT observations
  28. EP260329a: COLIBRÍ optical upper limit
  29. EP260329a: EP-FXT follow up observation
  30. EP260329a: NOT optical counterpart candidate
  31. GRB 260330A: Fermi GBM Final Real-time Localization
  32. EP260329b: Global MASTER-Net observations report
  33. Fermi trigger No 796485221: Global MASTER-Net observations report
  34. GRB 260327A: Insight-HXMT/HE detection
  35. EP260329b: Optical follow-up with Kinder observations
  36. EP 260329b: COLIBRÍ optical observations
  37. EP260329a: Optical upper limit with Kinder observations
  38. EP260329b: LCO optical observations of the counterpart
  39. GRB 260326A: Insight-HXMT/HE detection
  40. EP260329b: Einstein Probe detection of an X-ray transient
  41. EP260329a: Einstein Probe detection of an X-ray transient
  42. EP-WXT trigger 01709259209: TRT optical counterpart detection
  43. The EP-WXT trigger 01709259209 (EP260329b?): Las Cumbres discovery of the optical counterpart
  44. GRID detection of GRB 260326A
  45. GRB 260310A: Gemini-North Spectral Confirmation of Supernova Features
  46. EP260327a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  47. EP260327a: SVOM/VT optical upper limits
  48. SMA Detection of GRB 260310A / AT 2026fgk
  49. GRB 260307B: ATCA Radio Upper Limits
  50. EP260327a: WINTER J-band upper limit
  51. EP260327a: COLIBRÍ optical upper limits
  52. GRB 260327A: AstroSat CZTI detection of a long burst
  53. EP260327a: Gemini-North optical upper limits
  54. EP260324a: GROWTH-India Telescope optical observation
  55. EP260327a: Global MASTER-Net observations report
  56. EP260327a: Einstein Probe detection of an X-ray transient
  57. GRB 260310A / AT 2026fgk: COLIBRÍ photometric evidence of the emerging supernova
  58. GRB 260310A: OSIRIS+/GTC spectroscopic detection of the associated BL-Ic, SN 2026fgk
  59. The EP-WXT trigger 01709259173 is likely a flaring star
  60. GRB 260310A / AT2026fgk: Late-time infrared detection with MIRAGE on the MDM 1.3m telescope
  61. IPN triangulation of GRB 260320A
  62. EP260324a: ZTF discovery of the optical counterpart ZTF26aapviim/AT2026hir
  63. GRB 260310A / AT2026fgk: R- and I-band observations with the PKU 60 cm optical telescope
  64. GRB 260326A: Fermi GBM Detection
  65. EP260321a: JinShan near-infrared observations
  66. GRB 260325A: Fermi GBM Final Localization
  67. GRB 260326A: Fermi GBM Final Real-time Localization
  68. EP260321a: Upper limits from a neutrino search with IceCube
  69. Fermi Gamma-ray Burst Monitor trigger 796145512/260325647 is not a GRB
  70. GRB 260310A/AT2026fgk: Kilonova-Catcher late optical afterglow detection at about 15 days post trigger time
  71. IPN triangulation of GRB 260316B
  72. EP260321a: J-band observations by the SYSU 80 cm infrared telescope
  73. GRID detection of GRB 260320A
  74. EP260321a: Gemini-South confirmation of a supernova (duplicate submission)
  75. EP260321a: Gemini-South confirmation of a supernova
  76. Fermi Gamma-ray Burst Monitor trigger 796060650/260324665 is not a GRB
  77. EP260321a: VLT/FORS2 spectroscopy confirmation of an associated type Ic-BL supernova SN 2026gzf
  78. GRB 260310A: LBT optical observations
  79. EP260321A: Mondy optical observations
  80. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limits at the FXT positions
  81. EP-WXT trigger 01709259112: confirmation of a stellar flare by BOOTES-5 & BOOTES-7
  82. GRB 260316B: CALET Gamma-Ray Burst Monitor detection
  83. The EP-WXT trigger 01709259112 is likely a flaring star
  84. Fermi GRB 260323A: Global MASTER-Net observations report
  85. GRB 260323A: Fermi GBM Final Real-time Localization
  86. GRB260310A: Palomar 60-inch photometry of an extremely bright late-time afterglow with a temporal break at 8 days
  87. GRB 260310A/AT2026fgk: Detection of temporal steepening in Einstein Probe X-ray data
  88. GRB 260322A: Fermi GBM Final Localization
  89. GRB 260320A: Glowbug gamma-ray detection
  90. EP260321a / AT2026gzf: VLT/X-shooter detection of supernova-like spectral features at z = 0.0344
  91. EP260321a: COLIBRÍ further optical observations and brightening
  92. Fermi Gamma-ray Burst Monitor trigger 795918973/260323025 is not a GRB
  93. EP260321a: Continued brightening from Kinder follow-up of the emerging supernova candidate
  94. EP260214b: ATCA 6 GHz detection
  95. EP260321a: Early TRT rising followed by JinShan decaying and then re-rising
  96. GRB 260321A: EP-FXT follow-up observation
  97. The EP-WXT trigger 01709259045 is likely a flaring star
  98. EP260321a: ZTF and Rubin detections of the candidate optical counterpart to EP260321a
  99. EP260321a: GOTO detection of blue variable source
  100. EP260321a: VLT imaging and spectroscopy show the variable source to be at z = 0.0343

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