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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. EP260324A / AT 2026hir: Spectroscopic Observations with the Next Generation Palomar Spectrograph
  2. GRB 260402B: Fermi GBM Final Real-time Localization
  3. GRB 260402A: WINTER J-band upper limit
  4. GRB260402A: GROWTH-India Telescope optical upper limit
  5. GRB 260402A / EP260402a: SVOM/VT optical upper limits
  6. EP260402a/GRB 260402A: SVOM/C-GFT upper limit
  7. GRB 260401A: SVOM/GRM observation
  8. GRB 260401A: GECAM-B observation
  9. EP260402a/GRB 260402A: Einstein Probe detection of an X-ray transient
  10. GRB 260402A: Kilonova-Catcher optical upper limit
  11. GRB 260402A: MASTER optical observations
  12. GRB 260402A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  13. GRB 260402A: SVOM/MXT candidate X-ray afterglow
  14. GRB 260402A: SVOM detection of a burst
  15. Fermi GRB 260401A: Global MASTER-Net observations report
  16. GRB 260401A: Fermi GBM Observation
  17. GRB 260401A: NuSTAR detection of prompt emission
  18. GRB 260401A: CALET Gamma-Ray Burst Monitor detection
  19. GRB 260401A: MAXI/GSC detection
  20. GRB 260401A: BALROG localization (Fermi Trigger 796733611 / GRB 260401454)
  21. GRB 260401A: Fermi GBM Final Real-time Localization
  22. EP260329b: Mondy and Assy-Turgen optical upper limits
  23. GRB 260310A / AT2026fgk: Luminance-band optical follow-up with a 28cm telescope in Daocheng
  24. EP260321a :Xinglong optical observations
  25. EP260327a: Xinglong optical upper limit
  26. EP260329b: GOTO detection of optical counterpart
  27. GRB 260330B: SVOM/VT optical upper limits
  28. Konus-Wind detection of GRB 260320A
  29. Konus-Wind detection of GRB 260316B (duplicate submission)
  30. Konus-Wind detection of GRB 260316B
  31. GRB 260321A: SVOM/ECLAIRs refined analysis
  32. EP260329b: J-band upper limits with WINTER
  33. EP260329a: J-band upper limit with WINTER
  34. GRB 260330A: Glowbug gamma-ray detection
  35. GRB 260310A: VLA Multi-frequency Radio Observations
  36. Fermi GBM Sub-Threshold Detection of GRB 260330B
  37. GRB 260330B: LCO optical upper limits
  38. GRB 260330B: SVOM detection of a burst
  39. EP260324a / AT2026hir: g- and r-band optical follow-up with the PKU 60cm Telescope
  40. EP260329b: refined analysis of the EP-WXT and EP-FXT observations
  41. EP260329a: COLIBRÍ optical upper limit
  42. EP260329a: EP-FXT follow up observation
  43. EP260329a: NOT optical counterpart candidate
  44. GRB 260330A: Fermi GBM Final Real-time Localization
  45. EP260329b: Global MASTER-Net observations report
  46. Fermi trigger No 796485221: Global MASTER-Net observations report
  47. GRB 260327A: Insight-HXMT/HE detection
  48. EP260329b: Optical follow-up with Kinder observations
  49. EP 260329b: COLIBRÍ optical observations
  50. EP260329a: Optical upper limit with Kinder observations
  51. EP260329b: LCO optical observations of the counterpart
  52. GRB 260326A: Insight-HXMT/HE detection
  53. EP260329b: Einstein Probe detection of an X-ray transient
  54. EP260329a: Einstein Probe detection of an X-ray transient
  55. EP-WXT trigger 01709259209: TRT optical counterpart detection
  56. The EP-WXT trigger 01709259209 (EP260329b?): Las Cumbres discovery of the optical counterpart
  57. GRID detection of GRB 260326A
  58. GRB 260310A: Gemini-North Spectral Confirmation of Supernova Features
  59. EP260327a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  60. EP260327a: SVOM/VT optical upper limits
  61. SMA Detection of GRB 260310A / AT 2026fgk
  62. GRB 260307B: ATCA Radio Upper Limits
  63. EP260327a: WINTER J-band upper limit
  64. EP260327a: COLIBRÍ optical upper limits
  65. GRB 260327A: AstroSat CZTI detection of a long burst
  66. EP260327a: Gemini-North optical upper limits
  67. EP260324a: GROWTH-India Telescope optical observation
  68. EP260327a: Global MASTER-Net observations report
  69. EP260327a: Einstein Probe detection of an X-ray transient
  70. GRB 260310A / AT 2026fgk: COLIBRÍ photometric evidence of the emerging supernova
  71. GRB 260310A: OSIRIS+/GTC spectroscopic detection of the associated BL-Ic, SN 2026fgk
  72. The EP-WXT trigger 01709259173 is likely a flaring star
  73. GRB 260310A / AT2026fgk: Late-time infrared detection with MIRAGE on the MDM 1.3m telescope
  74. IPN triangulation of GRB 260320A
  75. EP260324a: ZTF discovery of the optical counterpart ZTF26aapviim/AT2026hir
  76. GRB 260310A / AT2026fgk: R- and I-band observations with the PKU 60 cm optical telescope
  77. GRB 260326A: Fermi GBM Detection
  78. EP260321a: JinShan near-infrared observations
  79. GRB 260325A: Fermi GBM Final Localization
  80. GRB 260326A: Fermi GBM Final Real-time Localization
  81. EP260321a: Upper limits from a neutrino search with IceCube
  82. Fermi Gamma-ray Burst Monitor trigger 796145512/260325647 is not a GRB
  83. GRB 260310A/AT2026fgk: Kilonova-Catcher late optical afterglow detection at about 15 days post trigger time
  84. IPN triangulation of GRB 260316B
  85. EP260321a: J-band observations by the SYSU 80 cm infrared telescope
  86. GRID detection of GRB 260320A
  87. EP260321a: Gemini-South confirmation of a supernova (duplicate submission)
  88. EP260321a: Gemini-South confirmation of a supernova
  89. Fermi Gamma-ray Burst Monitor trigger 796060650/260324665 is not a GRB
  90. EP260321a: VLT/FORS2 spectroscopy confirmation of an associated type Ic-BL supernova SN 2026gzf
  91. GRB 260310A: LBT optical observations
  92. EP260321A: Mondy optical observations
  93. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limits at the FXT positions
  94. EP-WXT trigger 01709259112: confirmation of a stellar flare by BOOTES-5 & BOOTES-7
  95. GRB 260316B: CALET Gamma-Ray Burst Monitor detection
  96. The EP-WXT trigger 01709259112 is likely a flaring star
  97. Fermi GRB 260323A: Global MASTER-Net observations report
  98. GRB 260323A: Fermi GBM Final Real-time Localization
  99. GRB260310A: Palomar 60-inch photometry of an extremely bright late-time afterglow with a temporal break at 8 days
  100. GRB 260310A/AT2026fgk: Detection of temporal steepening in Einstein Probe X-ray data

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