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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: WINTER J-band upper limit
  2. GRB260402A: GROWTH-India Telescope optical upper limit
  3. GRB 260402A / EP260402a: SVOM/VT optical upper limits
  4. EP260402a/GRB 260402A: SVOM/C-GFT upper limit
  5. GRB 260401A: SVOM/GRM observation
  6. GRB 260401A: GECAM-B observation
  7. EP260402a/GRB 260402A: Einstein Probe detection of an X-ray transient
  8. GRB 260402A: Kilonova-Catcher optical upper limit
  9. GRB 260402A: MASTER optical observations
  10. GRB 260402A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  11. GRB 260402A: SVOM/MXT candidate X-ray afterglow
  12. GRB 260402A: SVOM detection of a burst
  13. Fermi GRB 260401A: Global MASTER-Net observations report
  14. GRB 260401A: Fermi GBM Observation
  15. GRB 260401A: NuSTAR detection of prompt emission
  16. GRB 260401A: CALET Gamma-Ray Burst Monitor detection
  17. GRB 260401A: MAXI/GSC detection
  18. GRB 260401A: BALROG localization (Fermi Trigger 796733611 / GRB 260401454)
  19. GRB 260401A: Fermi GBM Final Real-time Localization
  20. EP260329b: Mondy and Assy-Turgen optical upper limits
  21. GRB 260310A / AT2026fgk: Luminance-band optical follow-up with a 28cm telescope in Daocheng
  22. EP260321a :Xinglong optical observations
  23. EP260327a: Xinglong optical upper limit
  24. EP260329b: GOTO detection of optical counterpart
  25. GRB 260330B: SVOM/VT optical upper limits
  26. Konus-Wind detection of GRB 260320A
  27. Konus-Wind detection of GRB 260316B (duplicate submission)
  28. Konus-Wind detection of GRB 260316B
  29. GRB 260321A: SVOM/ECLAIRs refined analysis
  30. EP260329b: J-band upper limits with WINTER
  31. EP260329a: J-band upper limit with WINTER
  32. GRB 260330A: Glowbug gamma-ray detection
  33. GRB 260310A: VLA Multi-frequency Radio Observations
  34. Fermi GBM Sub-Threshold Detection of GRB 260330B
  35. GRB 260330B: LCO optical upper limits
  36. GRB 260330B: SVOM detection of a burst
  37. EP260324a / AT2026hir: g- and r-band optical follow-up with the PKU 60cm Telescope
  38. EP260329b: refined analysis of the EP-WXT and EP-FXT observations
  39. EP260329a: COLIBRÍ optical upper limit
  40. EP260329a: EP-FXT follow up observation
  41. EP260329a: NOT optical counterpart candidate
  42. GRB 260330A: Fermi GBM Final Real-time Localization
  43. EP260329b: Global MASTER-Net observations report
  44. Fermi trigger No 796485221: Global MASTER-Net observations report
  45. GRB 260327A: Insight-HXMT/HE detection
  46. EP260329b: Optical follow-up with Kinder observations
  47. EP 260329b: COLIBRÍ optical observations
  48. EP260329a: Optical upper limit with Kinder observations
  49. EP260329b: LCO optical observations of the counterpart
  50. GRB 260326A: Insight-HXMT/HE detection
  51. EP260329b: Einstein Probe detection of an X-ray transient
  52. EP260329a: Einstein Probe detection of an X-ray transient
  53. EP-WXT trigger 01709259209: TRT optical counterpart detection
  54. The EP-WXT trigger 01709259209 (EP260329b?): Las Cumbres discovery of the optical counterpart
  55. GRID detection of GRB 260326A
  56. GRB 260310A: Gemini-North Spectral Confirmation of Supernova Features
  57. EP260327a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  58. EP260327a: SVOM/VT optical upper limits
  59. SMA Detection of GRB 260310A / AT 2026fgk
  60. GRB 260307B: ATCA Radio Upper Limits
  61. EP260327a: WINTER J-band upper limit
  62. EP260327a: COLIBRÍ optical upper limits
  63. GRB 260327A: AstroSat CZTI detection of a long burst
  64. EP260327a: Gemini-North optical upper limits
  65. EP260324a: GROWTH-India Telescope optical observation
  66. EP260327a: Global MASTER-Net observations report
  67. EP260327a: Einstein Probe detection of an X-ray transient
  68. GRB 260310A / AT 2026fgk: COLIBRÍ photometric evidence of the emerging supernova
  69. GRB 260310A: OSIRIS+/GTC spectroscopic detection of the associated BL-Ic, SN 2026fgk
  70. The EP-WXT trigger 01709259173 is likely a flaring star
  71. GRB 260310A / AT2026fgk: Late-time infrared detection with MIRAGE on the MDM 1.3m telescope
  72. IPN triangulation of GRB 260320A
  73. EP260324a: ZTF discovery of the optical counterpart ZTF26aapviim/AT2026hir
  74. GRB 260310A / AT2026fgk: R- and I-band observations with the PKU 60 cm optical telescope
  75. GRB 260326A: Fermi GBM Detection
  76. EP260321a: JinShan near-infrared observations
  77. GRB 260325A: Fermi GBM Final Localization
  78. GRB 260326A: Fermi GBM Final Real-time Localization
  79. EP260321a: Upper limits from a neutrino search with IceCube
  80. Fermi Gamma-ray Burst Monitor trigger 796145512/260325647 is not a GRB
  81. GRB 260310A/AT2026fgk: Kilonova-Catcher late optical afterglow detection at about 15 days post trigger time
  82. IPN triangulation of GRB 260316B
  83. EP260321a: J-band observations by the SYSU 80 cm infrared telescope
  84. GRID detection of GRB 260320A
  85. EP260321a: Gemini-South confirmation of a supernova (duplicate submission)
  86. EP260321a: Gemini-South confirmation of a supernova
  87. Fermi Gamma-ray Burst Monitor trigger 796060650/260324665 is not a GRB
  88. EP260321a: VLT/FORS2 spectroscopy confirmation of an associated type Ic-BL supernova SN 2026gzf
  89. GRB 260310A: LBT optical observations
  90. EP260321A: Mondy optical observations
  91. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limits at the FXT positions
  92. EP-WXT trigger 01709259112: confirmation of a stellar flare by BOOTES-5 & BOOTES-7
  93. GRB 260316B: CALET Gamma-Ray Burst Monitor detection
  94. The EP-WXT trigger 01709259112 is likely a flaring star
  95. Fermi GRB 260323A: Global MASTER-Net observations report
  96. GRB 260323A: Fermi GBM Final Real-time Localization
  97. GRB260310A: Palomar 60-inch photometry of an extremely bright late-time afterglow with a temporal break at 8 days
  98. GRB 260310A/AT2026fgk: Detection of temporal steepening in Einstein Probe X-ray data
  99. GRB 260322A: Fermi GBM Final Localization
  100. GRB 260320A: Glowbug gamma-ray detection

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