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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. GRB260402A: GROWTH-India Telescope optical 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. EP260321a :Xinglong optical observations
  22. EP260327a: Xinglong optical upper limit
  23. EP260329b: GOTO detection of optical counterpart
  24. GRB 260330B: SVOM/VT optical upper limits
  25. Konus-Wind detection of GRB 260320A
  26. Konus-Wind detection of GRB 260316B (duplicate submission)
  27. Konus-Wind detection of GRB 260316B
  28. GRB 260321A: SVOM/ECLAIRs refined analysis
  29. EP260329b: J-band upper limits with WINTER
  30. EP260329a: J-band upper limit with WINTER
  31. GRB 260330A: Glowbug gamma-ray detection
  32. GRB 260310A: VLA Multi-frequency Radio Observations
  33. Fermi GBM Sub-Threshold Detection of GRB 260330B
  34. GRB 260330B: LCO optical upper limits
  35. GRB 260330B: SVOM detection of a burst
  36. EP260324a / AT2026hir: g- and r-band optical follow-up with the PKU 60cm Telescope
  37. EP260329b: refined analysis of the EP-WXT and EP-FXT observations
  38. EP260329a: COLIBRÍ optical upper limit
  39. EP260329a: EP-FXT follow up observation
  40. EP260329a: NOT optical counterpart candidate
  41. GRB 260330A: Fermi GBM Final Real-time Localization
  42. EP260329b: Global MASTER-Net observations report
  43. Fermi trigger No 796485221: Global MASTER-Net observations report
  44. GRB 260327A: Insight-HXMT/HE detection
  45. EP260329b: Optical follow-up with Kinder observations
  46. EP 260329b: COLIBRÍ optical observations
  47. EP260329a: Optical upper limit with Kinder observations
  48. EP260329b: LCO optical observations of the counterpart
  49. GRB 260326A: Insight-HXMT/HE detection
  50. EP260329b: Einstein Probe detection of an X-ray transient
  51. EP260329a: Einstein Probe detection of an X-ray transient
  52. EP-WXT trigger 01709259209: TRT optical counterpart detection
  53. The EP-WXT trigger 01709259209 (EP260329b?): Las Cumbres discovery of the optical counterpart
  54. GRID detection of GRB 260326A
  55. GRB 260310A: Gemini-North Spectral Confirmation of Supernova Features
  56. EP260327a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  57. EP260327a: SVOM/VT optical upper limits
  58. SMA Detection of GRB 260310A / AT 2026fgk
  59. GRB 260307B: ATCA Radio Upper Limits
  60. EP260327a: WINTER J-band upper limit
  61. EP260327a: COLIBRÍ optical upper limits
  62. GRB 260327A: AstroSat CZTI detection of a long burst
  63. EP260327a: Gemini-North optical upper limits
  64. EP260324a: GROWTH-India Telescope optical observation
  65. EP260327a: Global MASTER-Net observations report
  66. EP260327a: Einstein Probe detection of an X-ray transient
  67. GRB 260310A / AT 2026fgk: COLIBRÍ photometric evidence of the emerging supernova
  68. GRB 260310A: OSIRIS+/GTC spectroscopic detection of the associated BL-Ic, SN 2026fgk
  69. The EP-WXT trigger 01709259173 is likely a flaring star
  70. GRB 260310A / AT2026fgk: Late-time infrared detection with MIRAGE on the MDM 1.3m telescope
  71. IPN triangulation of GRB 260320A
  72. EP260324a: ZTF discovery of the optical counterpart ZTF26aapviim/AT2026hir
  73. GRB 260310A / AT2026fgk: R- and I-band observations with the PKU 60 cm optical telescope
  74. GRB 260326A: Fermi GBM Detection
  75. EP260321a: JinShan near-infrared observations
  76. GRB 260325A: Fermi GBM Final Localization
  77. GRB 260326A: Fermi GBM Final Real-time Localization
  78. EP260321a: Upper limits from a neutrino search with IceCube
  79. Fermi Gamma-ray Burst Monitor trigger 796145512/260325647 is not a GRB
  80. GRB 260310A/AT2026fgk: Kilonova-Catcher late optical afterglow detection at about 15 days post trigger time
  81. IPN triangulation of GRB 260316B
  82. EP260321a: J-band observations by the SYSU 80 cm infrared telescope
  83. GRID detection of GRB 260320A
  84. EP260321a: Gemini-South confirmation of a supernova (duplicate submission)
  85. EP260321a: Gemini-South confirmation of a supernova
  86. Fermi Gamma-ray Burst Monitor trigger 796060650/260324665 is not a GRB
  87. EP260321a: VLT/FORS2 spectroscopy confirmation of an associated type Ic-BL supernova SN 2026gzf
  88. GRB 260310A: LBT optical observations
  89. EP260321A: Mondy optical observations
  90. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limits at the FXT positions
  91. EP-WXT trigger 01709259112: confirmation of a stellar flare by BOOTES-5 & BOOTES-7
  92. GRB 260316B: CALET Gamma-Ray Burst Monitor detection
  93. The EP-WXT trigger 01709259112 is likely a flaring star
  94. Fermi GRB 260323A: Global MASTER-Net observations report
  95. GRB 260323A: Fermi GBM Final Real-time Localization
  96. GRB260310A: Palomar 60-inch photometry of an extremely bright late-time afterglow with a temporal break at 8 days
  97. GRB 260310A/AT2026fgk: Detection of temporal steepening in Einstein Probe X-ray data
  98. GRB 260322A: Fermi GBM Final Localization
  99. GRB 260320A: Glowbug gamma-ray detection
  100. EP260321a / AT2026gzf: VLT/X-shooter detection of supernova-like spectral features at z = 0.0344

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