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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. Fermi trigger No 796485221: Global MASTER-Net observations report
  2. GRB 260327A: Insight-HXMT/HE detection
  3. EP260329b: Optical follow-up with Kinder observations
  4. EP 260329b: COLIBRÍ optical observations
  5. EP260329a: Optical upper limit with Kinder observations
  6. EP260329b: LCO optical observations of the counterpart
  7. GRB 260326A: Insight-HXMT/HE detection
  8. EP260329b: Einstein Probe detection of an X-ray transient
  9. EP260329a: Einstein Probe detection of an X-ray transient
  10. EP-WXT trigger 01709259209: TRT optical counterpart detection
  11. The EP-WXT trigger 01709259209 (EP260329b?): Las Cumbres discovery of the optical counterpart
  12. GRID detection of GRB 260326A
  13. GRB 260310A: Gemini-North Spectral Confirmation of Supernova Features
  14. EP260327a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  15. EP260327a: SVOM/VT optical upper limits
  16. SMA Detection of GRB 260310A / AT 2026fgk
  17. GRB 260307B: ATCA Radio Upper Limits
  18. EP260327a: WINTER J-band upper limit
  19. EP260327a: COLIBRÍ optical upper limits
  20. GRB 260327A: AstroSat CZTI detection of a long burst
  21. EP260327a: Gemini-North optical upper limits
  22. EP260324a: GROWTH-India Telescope optical observation
  23. EP260327a: Global MASTER-Net observations report
  24. EP260327a: Einstein Probe detection of an X-ray transient
  25. GRB 260310A / AT 2026fgk: COLIBRÍ photometric evidence of the emerging supernova
  26. GRB 260310A: OSIRIS+/GTC spectroscopic detection of the associated BL-Ic, SN 2026fgk
  27. The EP-WXT trigger 01709259173 is likely a flaring star
  28. GRB 260310A / AT2026fgk: Late-time infrared detection with MIRAGE on the MDM 1.3m telescope
  29. IPN triangulation of GRB 260320A
  30. EP260324a: ZTF discovery of the optical counterpart ZTF26aapviim/AT2026hir
  31. GRB 260310A / AT2026fgk: R- and I-band observations with the PKU 60 cm optical telescope
  32. GRB 260326A: Fermi GBM Detection
  33. EP260321a: JinShan near-infrared observations
  34. GRB 260325A: Fermi GBM Final Localization
  35. GRB 260326A: Fermi GBM Final Real-time Localization
  36. EP260321a: Upper limits from a neutrino search with IceCube
  37. Fermi Gamma-ray Burst Monitor trigger 796145512/260325647 is not a GRB
  38. GRB 260310A/AT2026fgk: Kilonova-Catcher late optical afterglow detection at about 15 days post trigger time
  39. IPN triangulation of GRB 260316B
  40. EP260321a: J-band observations by the SYSU 80 cm infrared telescope
  41. GRID detection of GRB 260320A
  42. EP260321a: Gemini-South confirmation of a supernova (duplicate submission)
  43. EP260321a: Gemini-South confirmation of a supernova
  44. Fermi Gamma-ray Burst Monitor trigger 796060650/260324665 is not a GRB
  45. EP260321a: VLT/FORS2 spectroscopy confirmation of an associated type Ic-BL supernova SN 2026gzf
  46. GRB 260310A: LBT optical observations
  47. EP260321A: Mondy optical observations
  48. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limits at the FXT positions
  49. EP-WXT trigger 01709259112: confirmation of a stellar flare by BOOTES-5 & BOOTES-7
  50. GRB 260316B: CALET Gamma-Ray Burst Monitor detection
  51. The EP-WXT trigger 01709259112 is likely a flaring star
  52. Fermi GRB 260323A: Global MASTER-Net observations report
  53. GRB 260323A: Fermi GBM Final Real-time Localization
  54. GRB260310A: Palomar 60-inch photometry of an extremely bright late-time afterglow with a temporal break at 8 days
  55. GRB 260310A/AT2026fgk: Detection of temporal steepening in Einstein Probe X-ray data
  56. GRB 260322A: Fermi GBM Final Localization
  57. GRB 260320A: Glowbug gamma-ray detection
  58. EP260321a / AT2026gzf: VLT/X-shooter detection of supernova-like spectral features at z = 0.0344
  59. EP260321a: COLIBRÍ further optical observations and brightening
  60. Fermi Gamma-ray Burst Monitor trigger 795918973/260323025 is not a GRB
  61. EP260321a: Continued brightening from Kinder follow-up of the emerging supernova candidate
  62. EP260214b: ATCA 6 GHz detection
  63. EP260321a: Early TRT rising followed by JinShan decaying and then re-rising
  64. GRB 260321A: EP-FXT follow-up observation
  65. The EP-WXT trigger 01709259045 is likely a flaring star
  66. EP260321a: ZTF and Rubin detections of the candidate optical counterpart to EP260321a
  67. EP260321a: GOTO detection of blue variable source
  68. EP260321a: VLT imaging and spectroscopy show the variable source to be at z = 0.0343
  69. EP260321a: further Kinder optical observations
  70. GRB 260321A: SVOM/VT optical upper limits
  71. EP260321a: Las Cumbres upper limit
  72. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  73. GRB 260320A: Insight-HXMT/HE detection
  74. EP260321a: COLIBRÍ optical upper limit on any supernova shock breakout emission
  75. EP260321a: refined analysis of the EP-WXT and EP-FXT observations, implying a possible supernova shock breakout candidate
  76. EP260321a: SVOM/VT optical upper limit
  77. GRB 260310A: continued optical observation at Mondy
  78. Fermi GBM Sub-Threshold Detection of GRB 260321A
  79. GRB 260321A: SVOM detection of a burst
  80. EP260321a: Kinder observations detect a blue variable star and set limits on a source from the z =0.034 galaxy within the error circle
  81. EP260321a: Global MASTER-Net observations report
  82. EP260321a: Einstein Probe detection of an X-ray transient
  83. GRB 260310A / AT2026fgk: ABObservatory and NOCTIS new optical observations
  84. GRB 260318A: Glowbug gamma-ray detection
  85. GRB 260310A / AT 2026fgk: KAIT optical observations
  86. GRB 260320A: NuSTAR detection of prompt emission
  87. GRB 260310A / AT2026fgk: NuSTAR follow-up detection
  88. EP-WXT trigger 01709258989: KAIT confirmation of a stellar flare
  89. GRB 260310A / AT 2026fgk: FTW optical and NIR observations show no rebrightening
  90. GRB 260310A: no evidence of re-brightening up to 9.6 days in optical observation at Mondy
  91. GRB 260310A / AT 2026fgk: COLIBRÍ evidence of a late rebrightening
  92. GRB 260310A/AT2026fgk: LBT near-infrared observations
  93. NOEMA Detection of GRB 260310A / AT 2026fgk
  94. EP-WXT trigger 01709258989: confirmation of a stellar flare by BOOTES-7
  95. GRB 260318A: SVOM/GRM observation
  96. The EP-WXT trigger 01709258989 is likely a flaring star
  97. GRB 260310A: classification as long GRB based on Eiso, Ep, and T_90
  98. GRB 260318A: GECAM-B observation
  99. GRB260310A/AT2026fgk: Further optical observation from 1.3m DFOT
  100. Fermi GRB 260318A: Global MASTER-Net observations report

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