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

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