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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 260330B: SVOM/VT optical upper limits
  2. Konus-Wind detection of GRB 260320A
  3. Konus-Wind detection of GRB 260316B (duplicate submission)
  4. Konus-Wind detection of GRB 260316B
  5. GRB 260321A: SVOM/ECLAIRs refined analysis
  6. EP260329b: J-band upper limits with WINTER
  7. EP260329a: J-band upper limit with WINTER
  8. GRB 260330A: Glowbug gamma-ray detection
  9. GRB 260310A: VLA Multi-frequency Radio Observations
  10. Fermi GBM Sub-Threshold Detection of GRB 260330B
  11. GRB 260330B: LCO optical upper limits
  12. GRB 260330B: SVOM detection of a burst
  13. EP260324a / AT2026hir: g- and r-band optical follow-up with the PKU 60cm Telescope
  14. EP260329b: refined analysis of the EP-WXT and EP-FXT observations
  15. EP260329a: COLIBRÍ optical upper limit
  16. EP260329a: EP-FXT follow up observation
  17. EP260329a: NOT optical counterpart candidate
  18. GRB 260330A: Fermi GBM Final Real-time Localization
  19. EP260329b: Global MASTER-Net observations report
  20. Fermi trigger No 796485221: Global MASTER-Net observations report
  21. GRB 260327A: Insight-HXMT/HE detection
  22. EP260329b: Optical follow-up with Kinder observations
  23. EP 260329b: COLIBRÍ optical observations
  24. EP260329a: Optical upper limit with Kinder observations
  25. EP260329b: LCO optical observations of the counterpart
  26. GRB 260326A: Insight-HXMT/HE detection
  27. EP260329b: Einstein Probe detection of an X-ray transient
  28. EP260329a: Einstein Probe detection of an X-ray transient
  29. EP-WXT trigger 01709259209: TRT optical counterpart detection
  30. The EP-WXT trigger 01709259209 (EP260329b?): Las Cumbres discovery of the optical counterpart
  31. GRID detection of GRB 260326A
  32. GRB 260310A: Gemini-North Spectral Confirmation of Supernova Features
  33. EP260327a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  34. EP260327a: SVOM/VT optical upper limits
  35. SMA Detection of GRB 260310A / AT 2026fgk
  36. GRB 260307B: ATCA Radio Upper Limits
  37. EP260327a: WINTER J-band upper limit
  38. EP260327a: COLIBRÍ optical upper limits
  39. GRB 260327A: AstroSat CZTI detection of a long burst
  40. EP260327a: Gemini-North optical upper limits
  41. EP260324a: GROWTH-India Telescope optical observation
  42. EP260327a: Global MASTER-Net observations report
  43. EP260327a: Einstein Probe detection of an X-ray transient
  44. GRB 260310A / AT 2026fgk: COLIBRÍ photometric evidence of the emerging supernova
  45. GRB 260310A: OSIRIS+/GTC spectroscopic detection of the associated BL-Ic, SN 2026fgk
  46. The EP-WXT trigger 01709259173 is likely a flaring star
  47. GRB 260310A / AT2026fgk: Late-time infrared detection with MIRAGE on the MDM 1.3m telescope
  48. IPN triangulation of GRB 260320A
  49. EP260324a: ZTF discovery of the optical counterpart ZTF26aapviim/AT2026hir
  50. GRB 260310A / AT2026fgk: R- and I-band observations with the PKU 60 cm optical telescope
  51. GRB 260326A: Fermi GBM Detection
  52. EP260321a: JinShan near-infrared observations
  53. GRB 260325A: Fermi GBM Final Localization
  54. GRB 260326A: Fermi GBM Final Real-time Localization
  55. EP260321a: Upper limits from a neutrino search with IceCube
  56. Fermi Gamma-ray Burst Monitor trigger 796145512/260325647 is not a GRB
  57. GRB 260310A/AT2026fgk: Kilonova-Catcher late optical afterglow detection at about 15 days post trigger time
  58. IPN triangulation of GRB 260316B
  59. EP260321a: J-band observations by the SYSU 80 cm infrared telescope
  60. GRID detection of GRB 260320A
  61. EP260321a: Gemini-South confirmation of a supernova (duplicate submission)
  62. EP260321a: Gemini-South confirmation of a supernova
  63. Fermi Gamma-ray Burst Monitor trigger 796060650/260324665 is not a GRB
  64. EP260321a: VLT/FORS2 spectroscopy confirmation of an associated type Ic-BL supernova SN 2026gzf
  65. GRB 260310A: LBT optical observations
  66. EP260321A: Mondy optical observations
  67. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limits at the FXT positions
  68. EP-WXT trigger 01709259112: confirmation of a stellar flare by BOOTES-5 & BOOTES-7
  69. GRB 260316B: CALET Gamma-Ray Burst Monitor detection
  70. The EP-WXT trigger 01709259112 is likely a flaring star
  71. Fermi GRB 260323A: Global MASTER-Net observations report
  72. GRB 260323A: Fermi GBM Final Real-time Localization
  73. GRB260310A: Palomar 60-inch photometry of an extremely bright late-time afterglow with a temporal break at 8 days
  74. GRB 260310A/AT2026fgk: Detection of temporal steepening in Einstein Probe X-ray data
  75. GRB 260322A: Fermi GBM Final Localization
  76. GRB 260320A: Glowbug gamma-ray detection
  77. EP260321a / AT2026gzf: VLT/X-shooter detection of supernova-like spectral features at z = 0.0344
  78. EP260321a: COLIBRÍ further optical observations and brightening
  79. Fermi Gamma-ray Burst Monitor trigger 795918973/260323025 is not a GRB
  80. EP260321a: Continued brightening from Kinder follow-up of the emerging supernova candidate
  81. EP260214b: ATCA 6 GHz detection
  82. EP260321a: Early TRT rising followed by JinShan decaying and then re-rising
  83. GRB 260321A: EP-FXT follow-up observation
  84. The EP-WXT trigger 01709259045 is likely a flaring star
  85. EP260321a: ZTF and Rubin detections of the candidate optical counterpart to EP260321a
  86. EP260321a: GOTO detection of blue variable source
  87. EP260321a: VLT imaging and spectroscopy show the variable source to be at z = 0.0343
  88. EP260321a: further Kinder optical observations
  89. GRB 260321A: SVOM/VT optical upper limits
  90. EP260321a: Las Cumbres upper limit
  91. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  92. GRB 260320A: Insight-HXMT/HE detection
  93. EP260321a: COLIBRÍ optical upper limit on any supernova shock breakout emission
  94. EP260321a: refined analysis of the EP-WXT and EP-FXT observations, implying a possible supernova shock breakout candidate
  95. EP260321a: SVOM/VT optical upper limit
  96. GRB 260310A: continued optical observation at Mondy
  97. Fermi GBM Sub-Threshold Detection of GRB 260321A
  98. GRB 260321A: SVOM detection of a burst
  99. EP260321a: Kinder observations detect a blue variable star and set limits on a source from the z =0.034 galaxy within the error circle
  100. EP260321a: Global MASTER-Net observations report

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