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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"

35321 results found.

  1. GRB 260402A: WINTER J-band upper limit
  2. GRB 260402A / EP260402a: SVOM/VT optical upper limits
  3. EP260402a/GRB 260402A: SVOM/C-GFT upper limit
  4. GRB 260401A: SVOM/GRM observation
  5. GRB 260401A: GECAM-B observation
  6. EP260402a/GRB 260402A: Einstein Probe detection of an X-ray transient
  7. GRB 260402A: Kilonova-Catcher optical upper limit
  8. GRB 260402A: MASTER optical observations
  9. GRB 260402A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  10. GRB 260402A: SVOM/MXT candidate X-ray afterglow
  11. GRB 260402A: SVOM detection of a burst
  12. Fermi GRB 260401A: Global MASTER-Net observations report
  13. GRB 260401A: Fermi GBM Observation
  14. GRB 260401A: NuSTAR detection of prompt emission
  15. GRB 260401A: CALET Gamma-Ray Burst Monitor detection
  16. GRB 260401A: MAXI/GSC detection
  17. GRB 260401A: BALROG localization (Fermi Trigger 796733611 / GRB 260401454)
  18. GRB 260401A: Fermi GBM Final Real-time Localization
  19. EP260329b: Mondy and Assy-Turgen optical upper limits
  20. GRB 260310A / AT2026fgk: Luminance-band optical follow-up with a 28cm telescope in Daocheng
  21. EP260329b: GOTO detection of optical counterpart
  22. GRB 260330B: SVOM/VT optical upper limits
  23. Konus-Wind detection of GRB 260320A
  24. Konus-Wind detection of GRB 260316B (duplicate submission)
  25. Konus-Wind detection of GRB 260316B
  26. GRB 260321A: SVOM/ECLAIRs refined analysis
  27. EP260329b: J-band upper limits with WINTER
  28. EP260329a: J-band upper limit with WINTER
  29. GRB 260330A: Glowbug gamma-ray detection
  30. GRB 260310A: VLA Multi-frequency Radio Observations
  31. Fermi GBM Sub-Threshold Detection of GRB 260330B
  32. GRB 260330B: LCO optical upper limits
  33. GRB 260330B: SVOM detection of a burst
  34. GRB 260330A: Fermi GBM Final Real-time Localization
  35. GRB 260327A: Insight-HXMT/HE detection
  36. GRB 260326A: Insight-HXMT/HE detection
  37. GRID detection of GRB 260326A
  38. GRB 260310A: Gemini-North Spectral Confirmation of Supernova Features
  39. SMA Detection of GRB 260310A / AT 2026fgk
  40. GRB 260307B: ATCA Radio Upper Limits
  41. GRB 260327A: AstroSat CZTI detection of a long burst
  42. GRB 260310A / AT 2026fgk: COLIBRÍ photometric evidence of the emerging supernova
  43. GRB 260310A: OSIRIS+/GTC spectroscopic detection of the associated BL-Ic, SN 2026fgk
  44. GRB 260310A / AT2026fgk: Late-time infrared detection with MIRAGE on the MDM 1.3m telescope
  45. IPN triangulation of GRB 260320A
  46. GRB 260310A / AT2026fgk: R- and I-band observations with the PKU 60 cm optical telescope
  47. GRB 260326A: Fermi GBM Detection
  48. GRB 260325A: Fermi GBM Final Localization
  49. GRB 260326A: Fermi GBM Final Real-time Localization
  50. EP260321a: Upper limits from a neutrino search with IceCube
  51. Fermi Gamma-ray Burst Monitor trigger 796145512/260325647 is not a GRB
  52. GRB 260310A/AT2026fgk: Kilonova-Catcher late optical afterglow detection at about 15 days post trigger time
  53. IPN triangulation of GRB 260316B
  54. GRID detection of GRB 260320A
  55. Fermi Gamma-ray Burst Monitor trigger 796060650/260324665 is not a GRB
  56. EP260321a: VLT/FORS2 spectroscopy confirmation of an associated type Ic-BL supernova SN 2026gzf
  57. GRB 260310A: LBT optical observations
  58. EP260321A: Mondy optical observations
  59. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limits at the FXT positions
  60. GRB 260316B: CALET Gamma-Ray Burst Monitor detection
  61. Fermi GRB 260323A: Global MASTER-Net observations report
  62. GRB 260323A: Fermi GBM Final Real-time Localization
  63. GRB260310A: Palomar 60-inch photometry of an extremely bright late-time afterglow with a temporal break at 8 days
  64. GRB 260310A/AT2026fgk: Detection of temporal steepening in Einstein Probe X-ray data
  65. GRB 260322A: Fermi GBM Final Localization
  66. GRB 260320A: Glowbug gamma-ray detection
  67. Fermi Gamma-ray Burst Monitor trigger 795918973/260323025 is not a GRB
  68. GRB 260321A: EP-FXT follow-up observation
  69. GRB 260321A: SVOM/VT optical upper limits
  70. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  71. GRB 260320A: Insight-HXMT/HE detection
  72. GRB 260310A: continued optical observation at Mondy
  73. Fermi GBM Sub-Threshold Detection of GRB 260321A
  74. GRB 260321A: SVOM detection of a burst
  75. GRB 260310A / AT2026fgk: ABObservatory and NOCTIS new optical observations
  76. GRB 260318A: Glowbug gamma-ray detection
  77. GRB 260310A / AT 2026fgk: KAIT optical observations
  78. GRB 260320A: NuSTAR detection of prompt emission
  79. GRB 260310A / AT2026fgk: NuSTAR follow-up detection
  80. EP-WXT trigger 01709258989: KAIT confirmation of a stellar flare
  81. GRB 260310A / AT 2026fgk: FTW optical and NIR observations show no rebrightening
  82. GRB 260310A: no evidence of re-brightening up to 9.6 days in optical observation at Mondy
  83. GRB 260310A / AT 2026fgk: COLIBRÍ evidence of a late rebrightening
  84. GRB 260310A/AT2026fgk: LBT near-infrared observations
  85. NOEMA Detection of GRB 260310A / AT 2026fgk
  86. GRB 260318A: SVOM/GRM observation
  87. GRB 260310A: classification as long GRB based on Eiso, Ep, and T_90
  88. GRB 260318A: GECAM-B observation
  89. Fermi GRB 260318A: Global MASTER-Net observations report
  90. GRB 260318A: Fermi GBM Final Real-time Localization
  91. Fermi Gamma-ray Burst Monitor trigger 795096033/260312500 (GRB 260313A) is unlikely to be a GRB
  92. GRB 260316A / EP260316a: COLIBRÍ optical followup of counterpart candidate
  93. GRB 260310A / AT 2026fgk: radio detection with the VLA
  94. GRB 260310A / AT2026fgk: SVOM/VT optical observations
  95. GRB 260310A / AT2026fgk: LCO optical observations
  96. GRB 260317A: Fermi GBM Final Localization
  97. GRB 260316B: GECAM-B observation
  98. GRB 260316B: SVOM/GRM observation
  99. EP260316a / GRB 260316A: SVOM/VT optical upper limits
  100. GRB 260316B: AstroSat CZTI detection

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