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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 260330B: SVOM/VT optical candidate
  2. EP260403a: Einstein Probe detection of an X-ray transient
  3. GRB 260330B: EP-FXT follow-up and identification of candidate afterglow
  4. GRB 260403A: AstroSat CZTI detection
  5. EP260402a/GRB 260402A: refined analysis of the EP-WXT and EP-FXT observations
  6. GRB 260402B: GECAM-B observation
  7. EP260402a/GRB 260402A: Jinshan near-infrared upper limit
  8. GRB 260402C: NuSTAR detection of prompt emission
  9. GRB 260402C: AstroSat CZTI detection of a long burst
  10. EP260324A / AT 2026hir: COLIBRÍ optical observations
  11. GRB 260403A: Fermi GBM Final Real-time Localization
  12. EP260324A / AT 2026hir: Spectroscopic Observations with the Next Generation Palomar Spectrograph
  13. GRB 260402B: Fermi GBM Final Real-time Localization
  14. GRB 260402A: WINTER J-band upper limit
  15. GRB260402A: GROWTH-India Telescope optical upper limit
  16. GRB 260402A / EP260402a: SVOM/VT optical upper limits
  17. EP260402a/GRB 260402A: SVOM/C-GFT upper limit
  18. GRB 260401A: SVOM/GRM observation
  19. GRB 260401A: GECAM-B observation
  20. EP260402a/GRB 260402A: Einstein Probe detection of an X-ray transient
  21. GRB 260402A: Kilonova-Catcher optical upper limit
  22. GRB 260402A: MASTER optical observations
  23. GRB 260402A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  24. GRB 260402A: SVOM/MXT candidate X-ray afterglow
  25. GRB 260402A: SVOM detection of a burst
  26. Fermi GRB 260401A: Global MASTER-Net observations report
  27. GRB 260401A: Fermi GBM Observation
  28. GRB 260401A: NuSTAR detection of prompt emission
  29. GRB 260401A: CALET Gamma-Ray Burst Monitor detection
  30. GRB 260401A: MAXI/GSC detection
  31. GRB 260401A: BALROG localization (Fermi Trigger 796733611 / GRB 260401454)
  32. GRB 260401A: Fermi GBM Final Real-time Localization
  33. EP260329b: Mondy and Assy-Turgen optical upper limits
  34. GRB 260310A / AT2026fgk: Luminance-band optical follow-up with a 28cm telescope in Daocheng
  35. EP260321a :Xinglong optical observations
  36. EP260327a: Xinglong optical upper limit
  37. EP260329b: GOTO detection of optical counterpart
  38. GRB 260330B: SVOM/VT optical upper limits
  39. Konus-Wind detection of GRB 260320A
  40. Konus-Wind detection of GRB 260316B (duplicate submission)
  41. Konus-Wind detection of GRB 260316B
  42. GRB 260321A: SVOM/ECLAIRs refined analysis
  43. EP260329b: J-band upper limits with WINTER
  44. EP260329a: J-band upper limit with WINTER
  45. GRB 260330A: Glowbug gamma-ray detection
  46. GRB 260310A: VLA Multi-frequency Radio Observations
  47. Fermi GBM Sub-Threshold Detection of GRB 260330B
  48. GRB 260330B: LCO optical upper limits
  49. GRB 260330B: SVOM detection of a burst
  50. EP260324a / AT2026hir: g- and r-band optical follow-up with the PKU 60cm Telescope
  51. EP260329b: refined analysis of the EP-WXT and EP-FXT observations
  52. EP260329a: COLIBRÍ optical upper limit
  53. EP260329a: EP-FXT follow up observation
  54. EP260329a: NOT optical counterpart candidate
  55. GRB 260330A: Fermi GBM Final Real-time Localization
  56. EP260329b: Global MASTER-Net observations report
  57. Fermi trigger No 796485221: Global MASTER-Net observations report
  58. GRB 260327A: Insight-HXMT/HE detection
  59. EP260329b: Optical follow-up with Kinder observations
  60. EP 260329b: COLIBRÍ optical observations
  61. EP260329a: Optical upper limit with Kinder observations
  62. EP260329b: LCO optical observations of the counterpart
  63. GRB 260326A: Insight-HXMT/HE detection
  64. EP260329b: Einstein Probe detection of an X-ray transient
  65. EP260329a: Einstein Probe detection of an X-ray transient
  66. EP-WXT trigger 01709259209: TRT optical counterpart detection
  67. The EP-WXT trigger 01709259209 (EP260329b?): Las Cumbres discovery of the optical counterpart
  68. GRID detection of GRB 260326A
  69. GRB 260310A: Gemini-North Spectral Confirmation of Supernova Features
  70. EP260327a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  71. EP260327a: SVOM/VT optical upper limits
  72. SMA Detection of GRB 260310A / AT 2026fgk
  73. GRB 260307B: ATCA Radio Upper Limits
  74. EP260327a: WINTER J-band upper limit
  75. EP260327a: COLIBRÍ optical upper limits
  76. GRB 260327A: AstroSat CZTI detection of a long burst
  77. EP260327a: Gemini-North optical upper limits
  78. EP260324a: GROWTH-India Telescope optical observation
  79. EP260327a: Global MASTER-Net observations report
  80. EP260327a: Einstein Probe detection of an X-ray transient
  81. GRB 260310A / AT 2026fgk: COLIBRÍ photometric evidence of the emerging supernova
  82. GRB 260310A: OSIRIS+/GTC spectroscopic detection of the associated BL-Ic, SN 2026fgk
  83. The EP-WXT trigger 01709259173 is likely a flaring star
  84. GRB 260310A / AT2026fgk: Late-time infrared detection with MIRAGE on the MDM 1.3m telescope
  85. IPN triangulation of GRB 260320A
  86. EP260324a: ZTF discovery of the optical counterpart ZTF26aapviim/AT2026hir
  87. GRB 260310A / AT2026fgk: R- and I-band observations with the PKU 60 cm optical telescope
  88. GRB 260326A: Fermi GBM Detection
  89. EP260321a: JinShan near-infrared observations
  90. GRB 260325A: Fermi GBM Final Localization
  91. GRB 260326A: Fermi GBM Final Real-time Localization
  92. EP260321a: Upper limits from a neutrino search with IceCube
  93. Fermi Gamma-ray Burst Monitor trigger 796145512/260325647 is not a GRB
  94. GRB 260310A/AT2026fgk: Kilonova-Catcher late optical afterglow detection at about 15 days post trigger time
  95. IPN triangulation of GRB 260316B
  96. EP260321a: J-band observations by the SYSU 80 cm infrared telescope
  97. GRID detection of GRB 260320A
  98. EP260321a: Gemini-South confirmation of a supernova (duplicate submission)
  99. EP260321a: Gemini-South confirmation of a supernova
  100. Fermi Gamma-ray Burst Monitor trigger 796060650/260324665 is not a GRB

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