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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"

36681 results found.

  1. GRB 260402C: NuSTAR detection of prompt emission
  2. GRB 260402C: AstroSat CZTI detection of a long burst
  3. GRB 260403A: Fermi GBM Final Real-time Localization
  4. GRB 260402B: Fermi GBM Final Real-time Localization
  5. GRB 260402A: WINTER J-band upper limit
  6. GRB 260402A / EP260402a: SVOM/VT optical upper limits
  7. EP260402a/GRB 260402A: SVOM/C-GFT upper limit
  8. GRB 260401A: SVOM/GRM observation
  9. GRB 260401A: GECAM-B observation
  10. EP260402a/GRB 260402A: Einstein Probe detection of an X-ray transient
  11. GRB 260402A: Kilonova-Catcher optical upper limit
  12. GRB 260402A: MASTER optical observations
  13. GRB 260402A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  14. GRB 260402A: SVOM/MXT candidate X-ray afterglow
  15. GRB 260402A: SVOM detection of a burst
  16. Fermi GRB 260401A: Global MASTER-Net observations report
  17. GRB 260401A: Fermi GBM Observation
  18. GRB 260401A: NuSTAR detection of prompt emission
  19. GRB 260401A: CALET Gamma-Ray Burst Monitor detection
  20. GRB 260401A: MAXI/GSC detection
  21. GRB 260401A: BALROG localization (Fermi Trigger 796733611 / GRB 260401454)
  22. GRB 260401A: Fermi GBM Final Real-time Localization
  23. EP260329b: Mondy and Assy-Turgen optical upper limits
  24. GRB 260310A / AT2026fgk: Luminance-band optical follow-up with a 28cm telescope in Daocheng
  25. EP260329b: GOTO detection of optical counterpart
  26. GRB 260330B: SVOM/VT optical upper limits
  27. Konus-Wind detection of GRB 260320A
  28. Konus-Wind detection of GRB 260316B (duplicate submission)
  29. Konus-Wind detection of GRB 260316B
  30. GRB 260321A: SVOM/ECLAIRs refined analysis
  31. EP260329b: J-band upper limits with WINTER
  32. EP260329a: J-band upper limit with WINTER
  33. GRB 260330A: Glowbug gamma-ray detection
  34. GRB 260310A: VLA Multi-frequency Radio Observations
  35. Fermi GBM Sub-Threshold Detection of GRB 260330B
  36. GRB 260330B: LCO optical upper limits
  37. GRB 260330B: SVOM detection of a burst
  38. GRB 260330A: Fermi GBM Final Real-time Localization
  39. Fermi trigger No 796485221: Global MASTER-Net observations report
  40. GRB 260327A: Insight-HXMT/HE detection
  41. GRB 260326A: Insight-HXMT/HE detection
  42. GRID detection of GRB 260326A
  43. GRB 260310A: Gemini-North Spectral Confirmation of Supernova Features
  44. SMA Detection of GRB 260310A / AT 2026fgk
  45. GRB 260307B: ATCA Radio Upper Limits
  46. GRB 260327A: AstroSat CZTI detection of a long burst
  47. GRB 260310A / AT 2026fgk: COLIBRÍ photometric evidence of the emerging supernova
  48. GRB 260310A: OSIRIS+/GTC spectroscopic detection of the associated BL-Ic, SN 2026fgk
  49. GRB 260310A / AT2026fgk: Late-time infrared detection with MIRAGE on the MDM 1.3m telescope
  50. IPN triangulation of GRB 260320A
  51. GRB 260310A / AT2026fgk: R- and I-band observations with the PKU 60 cm optical telescope
  52. GRB 260326A: Fermi GBM Detection
  53. GRB 260325A: Fermi GBM Final Localization
  54. GRB 260326A: Fermi GBM Final Real-time Localization
  55. Fermi Gamma-ray Burst Monitor trigger 796145512/260325647 is not a GRB
  56. GRB 260310A/AT2026fgk: Kilonova-Catcher late optical afterglow detection at about 15 days post trigger time
  57. IPN triangulation of GRB 260316B
  58. GRID detection of GRB 260320A
  59. Fermi Gamma-ray Burst Monitor trigger 796060650/260324665 is not a GRB
  60. EP260321a: VLT/FORS2 spectroscopy confirmation of an associated type Ic-BL supernova SN 2026gzf
  61. GRB 260310A: LBT optical observations
  62. EP260321A: Mondy optical observations
  63. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limits at the FXT positions
  64. GRB 260316B: CALET Gamma-Ray Burst Monitor detection
  65. Fermi GRB 260323A: Global MASTER-Net observations report
  66. GRB 260323A: Fermi GBM Final Real-time Localization
  67. GRB260310A: Palomar 60-inch photometry of an extremely bright late-time afterglow with a temporal break at 8 days
  68. GRB 260310A/AT2026fgk: Detection of temporal steepening in Einstein Probe X-ray data
  69. GRB 260322A: Fermi GBM Final Localization
  70. GRB 260320A: Glowbug gamma-ray detection
  71. Fermi Gamma-ray Burst Monitor trigger 795918973/260323025 is not a GRB
  72. GRB 260321A: EP-FXT follow-up observation
  73. GRB 260321A: SVOM/VT optical upper limits
  74. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  75. GRB 260320A: Insight-HXMT/HE detection
  76. GRB 260310A: continued optical observation at Mondy
  77. Fermi GBM Sub-Threshold Detection of GRB 260321A
  78. GRB 260321A: SVOM detection of a burst
  79. GRB 260310A / AT2026fgk: ABObservatory and NOCTIS new optical observations
  80. GRB 260318A: Glowbug gamma-ray detection
  81. GRB 260310A / AT 2026fgk: KAIT optical observations
  82. GRB 260320A: NuSTAR detection of prompt emission
  83. GRB 260310A / AT2026fgk: NuSTAR follow-up detection
  84. EP-WXT trigger 01709258989: KAIT confirmation of a stellar flare
  85. GRB 260310A / AT 2026fgk: FTW optical and NIR observations show no rebrightening
  86. GRB 260310A: no evidence of re-brightening up to 9.6 days in optical observation at Mondy
  87. GRB 260310A / AT 2026fgk: COLIBRÍ evidence of a late rebrightening
  88. GRB 260310A/AT2026fgk: LBT near-infrared observations
  89. NOEMA Detection of GRB 260310A / AT 2026fgk
  90. GRB 260318A: SVOM/GRM observation
  91. GRB 260310A: classification as long GRB based on Eiso, Ep, and T_90
  92. GRB 260318A: GECAM-B observation
  93. GRB260310A/AT2026fgk: Further optical observation from 1.3m DFOT
  94. Fermi GRB 260318A: Global MASTER-Net observations report
  95. GRB 260318A: Fermi GBM Final Real-time Localization
  96. Fermi Gamma-ray Burst Monitor trigger 795096033/260312500 (GRB 260313A) is unlikely to be a GRB
  97. GRB 260316A / EP260316a: COLIBRÍ optical followup of counterpart candidate
  98. GRB 260310A / AT 2026fgk: radio detection with the VLA
  99. GRB 260310A / AT2026fgk: SVOM/VT optical observations
  100. GRB 260310A / AT2026fgk: LCO optical observations

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