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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. The EP-WXT trigger 01709259586 is likely a flaring star
  2. GRB 260330B: SVOM/VT further optical observation
  3. Fermi Gamma-ray Burst Monitor trigger 796931884/260403749 is not a GRB
  4. GRB 260330B: SVOM/ECLAIRs refined analysis
  5. EP260403a: LCO optical observations of the counterpart
  6. GRB 260310A/AT2026fgk: Kilonova-Catcher long term optical monitoring
  7. EP260403a: LCO optical counterpart detection
  8. EP260403a: COLIBRÍ optical counterpart candidate
  9. GRB 260330B: SVOM/VT optical candidate
  10. EP260403a: Einstein Probe detection of an X-ray transient
  11. GRB 260330B: EP-FXT follow-up and identification of candidate afterglow
  12. GRB 260403A: AstroSat CZTI detection
  13. EP260402a/GRB 260402A: refined analysis of the EP-WXT and EP-FXT observations
  14. GRB 260402B: GECAM-B observation
  15. EP260402a/GRB 260402A: Jinshan near-infrared upper limit
  16. GRB 260402C: NuSTAR detection of prompt emission
  17. GRB 260402C: AstroSat CZTI detection of a long burst
  18. EP260324A / AT 2026hir: COLIBRÍ optical observations
  19. GRB 260403A: Fermi GBM Final Real-time Localization
  20. EP260324A / AT 2026hir: Spectroscopic Observations with the Next Generation Palomar Spectrograph
  21. GRB 260402B: Fermi GBM Final Real-time Localization
  22. GRB 260402A: WINTER J-band upper limit
  23. GRB260402A: GROWTH-India Telescope optical upper limit
  24. GRB 260402A / EP260402a: SVOM/VT optical upper limits
  25. EP260402a/GRB 260402A: SVOM/C-GFT upper limit
  26. GRB 260401A: SVOM/GRM observation
  27. GRB 260401A: GECAM-B observation
  28. EP260402a/GRB 260402A: Einstein Probe detection of an X-ray transient
  29. GRB 260402A: Kilonova-Catcher optical upper limit
  30. GRB 260402A: MASTER optical observations
  31. GRB 260402A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  32. GRB 260402A: SVOM/MXT candidate X-ray afterglow
  33. GRB 260402A: SVOM detection of a burst
  34. Fermi GRB 260401A: Global MASTER-Net observations report
  35. GRB 260401A: Fermi GBM Observation
  36. GRB 260401A: NuSTAR detection of prompt emission
  37. GRB 260401A: CALET Gamma-Ray Burst Monitor detection
  38. GRB 260401A: MAXI/GSC detection
  39. GRB 260401A: BALROG localization (Fermi Trigger 796733611 / GRB 260401454)
  40. GRB 260401A: Fermi GBM Final Real-time Localization
  41. EP260329b: Mondy and Assy-Turgen optical upper limits
  42. GRB 260310A / AT2026fgk: Luminance-band optical follow-up with a 28cm telescope in Daocheng
  43. EP260321a :Xinglong optical observations
  44. EP260327a: Xinglong optical upper limit
  45. EP260329b: GOTO detection of optical counterpart
  46. GRB 260330B: SVOM/VT optical upper limits
  47. Konus-Wind detection of GRB 260320A
  48. Konus-Wind detection of GRB 260316B (duplicate submission)
  49. Konus-Wind detection of GRB 260316B
  50. GRB 260321A: SVOM/ECLAIRs refined analysis
  51. EP260329b: J-band upper limits with WINTER
  52. EP260329a: J-band upper limit with WINTER
  53. GRB 260330A: Glowbug gamma-ray detection
  54. GRB 260310A: VLA Multi-frequency Radio Observations
  55. Fermi GBM Sub-Threshold Detection of GRB 260330B
  56. GRB 260330B: LCO optical upper limits
  57. GRB 260330B: SVOM detection of a burst
  58. EP260324a / AT2026hir: g- and r-band optical follow-up with the PKU 60cm Telescope
  59. EP260329b: refined analysis of the EP-WXT and EP-FXT observations
  60. EP260329a: COLIBRÍ optical upper limit
  61. EP260329a: EP-FXT follow up observation
  62. EP260329a: NOT optical counterpart candidate
  63. GRB 260330A: Fermi GBM Final Real-time Localization
  64. EP260329b: Global MASTER-Net observations report
  65. Fermi trigger No 796485221: Global MASTER-Net observations report
  66. GRB 260327A: Insight-HXMT/HE detection
  67. EP260329b: Optical follow-up with Kinder observations
  68. EP 260329b: COLIBRÍ optical observations
  69. EP260329a: Optical upper limit with Kinder observations
  70. EP260329b: LCO optical observations of the counterpart
  71. GRB 260326A: Insight-HXMT/HE detection
  72. EP260329b: Einstein Probe detection of an X-ray transient
  73. EP260329a: Einstein Probe detection of an X-ray transient
  74. EP-WXT trigger 01709259209: TRT optical counterpart detection
  75. The EP-WXT trigger 01709259209 (EP260329b?): Las Cumbres discovery of the optical counterpart
  76. GRID detection of GRB 260326A
  77. GRB 260310A: Gemini-North Spectral Confirmation of Supernova Features
  78. EP260327a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  79. EP260327a: SVOM/VT optical upper limits
  80. SMA Detection of GRB 260310A / AT 2026fgk
  81. GRB 260307B: ATCA Radio Upper Limits
  82. EP260327a: WINTER J-band upper limit
  83. EP260327a: COLIBRÍ optical upper limits
  84. GRB 260327A: AstroSat CZTI detection of a long burst
  85. EP260327a: Gemini-North optical upper limits
  86. EP260324a: GROWTH-India Telescope optical observation
  87. EP260327a: Global MASTER-Net observations report
  88. EP260327a: Einstein Probe detection of an X-ray transient
  89. GRB 260310A / AT 2026fgk: COLIBRÍ photometric evidence of the emerging supernova
  90. GRB 260310A: OSIRIS+/GTC spectroscopic detection of the associated BL-Ic, SN 2026fgk
  91. The EP-WXT trigger 01709259173 is likely a flaring star
  92. GRB 260310A / AT2026fgk: Late-time infrared detection with MIRAGE on the MDM 1.3m telescope
  93. IPN triangulation of GRB 260320A
  94. EP260324a: ZTF discovery of the optical counterpart ZTF26aapviim/AT2026hir
  95. GRB 260310A / AT2026fgk: R- and I-band observations with the PKU 60 cm optical telescope
  96. GRB 260326A: Fermi GBM Detection
  97. EP260321a: JinShan near-infrared observations
  98. GRB 260325A: Fermi GBM Final Localization
  99. GRB 260326A: Fermi GBM Final Real-time Localization
  100. EP260321a: Upper limits from a neutrino search with IceCube

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