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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 260403A: AstroSat CZTI detection
  2. EP260402a/GRB 260402A: refined analysis of the EP-WXT and EP-FXT observations
  3. GRB 260402B: GECAM-B observation
  4. EP260402a/GRB 260402A: Jinshan near-infrared upper limit
  5. GRB 260402C: NuSTAR detection of prompt emission
  6. GRB 260402C: AstroSat CZTI detection of a long burst
  7. EP260324A / AT 2026hir: COLIBRÍ optical observations
  8. GRB 260403A: Fermi GBM Final Real-time Localization
  9. EP260324A / AT 2026hir: Spectroscopic Observations with the Next Generation Palomar Spectrograph
  10. GRB 260402B: Fermi GBM Final Real-time Localization
  11. GRB 260402A: WINTER J-band upper limit
  12. GRB260402A: GROWTH-India Telescope optical upper limit
  13. GRB 260402A / EP260402a: SVOM/VT optical upper limits
  14. EP260402a/GRB 260402A: SVOM/C-GFT upper limit
  15. GRB 260401A: SVOM/GRM observation
  16. GRB 260401A: GECAM-B observation
  17. EP260402a/GRB 260402A: Einstein Probe detection of an X-ray transient
  18. GRB 260402A: Kilonova-Catcher optical upper limit
  19. GRB 260402A: MASTER optical observations
  20. GRB 260402A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  21. GRB 260402A: SVOM/MXT candidate X-ray afterglow
  22. GRB 260402A: SVOM detection of a burst
  23. Fermi GRB 260401A: Global MASTER-Net observations report
  24. GRB 260401A: Fermi GBM Observation
  25. GRB 260401A: NuSTAR detection of prompt emission
  26. GRB 260401A: CALET Gamma-Ray Burst Monitor detection
  27. GRB 260401A: MAXI/GSC detection
  28. GRB 260401A: BALROG localization (Fermi Trigger 796733611 / GRB 260401454)
  29. GRB 260401A: Fermi GBM Final Real-time Localization
  30. EP260329b: Mondy and Assy-Turgen optical upper limits
  31. GRB 260310A / AT2026fgk: Luminance-band optical follow-up with a 28cm telescope in Daocheng
  32. EP260321a :Xinglong optical observations
  33. EP260327a: Xinglong optical upper limit
  34. EP260329b: GOTO detection of optical counterpart
  35. GRB 260330B: SVOM/VT optical upper limits
  36. Konus-Wind detection of GRB 260320A
  37. Konus-Wind detection of GRB 260316B (duplicate submission)
  38. Konus-Wind detection of GRB 260316B
  39. GRB 260321A: SVOM/ECLAIRs refined analysis
  40. EP260329b: J-band upper limits with WINTER
  41. EP260329a: J-band upper limit with WINTER
  42. GRB 260330A: Glowbug gamma-ray detection
  43. GRB 260310A: VLA Multi-frequency Radio Observations
  44. Fermi GBM Sub-Threshold Detection of GRB 260330B
  45. GRB 260330B: LCO optical upper limits
  46. GRB 260330B: SVOM detection of a burst
  47. EP260324a / AT2026hir: g- and r-band optical follow-up with the PKU 60cm Telescope
  48. EP260329b: refined analysis of the EP-WXT and EP-FXT observations
  49. EP260329a: COLIBRÍ optical upper limit
  50. EP260329a: EP-FXT follow up observation
  51. EP260329a: NOT optical counterpart candidate
  52. GRB 260330A: Fermi GBM Final Real-time Localization
  53. EP260329b: Global MASTER-Net observations report
  54. Fermi trigger No 796485221: Global MASTER-Net observations report
  55. GRB 260327A: Insight-HXMT/HE detection
  56. EP260329b: Optical follow-up with Kinder observations
  57. EP 260329b: COLIBRÍ optical observations
  58. EP260329a: Optical upper limit with Kinder observations
  59. EP260329b: LCO optical observations of the counterpart
  60. GRB 260326A: Insight-HXMT/HE detection
  61. EP260329b: Einstein Probe detection of an X-ray transient
  62. EP260329a: Einstein Probe detection of an X-ray transient
  63. EP-WXT trigger 01709259209: TRT optical counterpart detection
  64. The EP-WXT trigger 01709259209 (EP260329b?): Las Cumbres discovery of the optical counterpart
  65. GRID detection of GRB 260326A
  66. GRB 260310A: Gemini-North Spectral Confirmation of Supernova Features
  67. EP260327a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  68. EP260327a: SVOM/VT optical upper limits
  69. SMA Detection of GRB 260310A / AT 2026fgk
  70. GRB 260307B: ATCA Radio Upper Limits
  71. EP260327a: WINTER J-band upper limit
  72. EP260327a: COLIBRÍ optical upper limits
  73. GRB 260327A: AstroSat CZTI detection of a long burst
  74. EP260327a: Gemini-North optical upper limits
  75. EP260324a: GROWTH-India Telescope optical observation
  76. EP260327a: Global MASTER-Net observations report
  77. EP260327a: Einstein Probe detection of an X-ray transient
  78. GRB 260310A / AT 2026fgk: COLIBRÍ photometric evidence of the emerging supernova
  79. GRB 260310A: OSIRIS+/GTC spectroscopic detection of the associated BL-Ic, SN 2026fgk
  80. The EP-WXT trigger 01709259173 is likely a flaring star
  81. GRB 260310A / AT2026fgk: Late-time infrared detection with MIRAGE on the MDM 1.3m telescope
  82. IPN triangulation of GRB 260320A
  83. EP260324a: ZTF discovery of the optical counterpart ZTF26aapviim/AT2026hir
  84. GRB 260310A / AT2026fgk: R- and I-band observations with the PKU 60 cm optical telescope
  85. GRB 260326A: Fermi GBM Detection
  86. EP260321a: JinShan near-infrared observations
  87. GRB 260325A: Fermi GBM Final Localization
  88. GRB 260326A: Fermi GBM Final Real-time Localization
  89. EP260321a: Upper limits from a neutrino search with IceCube
  90. Fermi Gamma-ray Burst Monitor trigger 796145512/260325647 is not a GRB
  91. GRB 260310A/AT2026fgk: Kilonova-Catcher late optical afterglow detection at about 15 days post trigger time
  92. IPN triangulation of GRB 260316B
  93. EP260321a: J-band observations by the SYSU 80 cm infrared telescope
  94. GRID detection of GRB 260320A
  95. EP260321a: Gemini-South confirmation of a supernova (duplicate submission)
  96. EP260321a: Gemini-South confirmation of a supernova
  97. Fermi Gamma-ray Burst Monitor trigger 796060650/260324665 is not a GRB
  98. EP260321a: VLT/FORS2 spectroscopy confirmation of an associated type Ic-BL supernova SN 2026gzf
  99. GRB 260310A: LBT optical observations
  100. EP260321A: Mondy optical observations

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