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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. EP 260329b: COLIBRÍ optical observations
  2. EP260329a: Optical upper limit with Kinder observations
  3. EP260329b: LCO optical observations of the counterpart
  4. GRB 260326A: Insight-HXMT/HE detection
  5. EP260329b: Einstein Probe detection of an X-ray transient
  6. EP260329a: Einstein Probe detection of an X-ray transient
  7. EP-WXT trigger 01709259209: TRT optical counterpart detection
  8. The EP-WXT trigger 01709259209 (EP260329b?): Las Cumbres discovery of the optical counterpart
  9. GRID detection of GRB 260326A
  10. GRB 260310A: Gemini-North Spectral Confirmation of Supernova Features
  11. EP260327a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  12. EP260327a: SVOM/VT optical upper limits
  13. SMA Detection of GRB 260310A / AT 2026fgk
  14. GRB 260307B: ATCA Radio Upper Limits
  15. EP260327a: WINTER J-band upper limit
  16. EP260327a: COLIBRÍ optical upper limits
  17. GRB 260327A: AstroSat CZTI detection of a long burst
  18. EP260327a: Gemini-North optical upper limits
  19. EP260324a: GROWTH-India Telescope optical observation
  20. EP260327a: Global MASTER-Net observations report
  21. EP260327a: Einstein Probe detection of an X-ray transient
  22. GRB 260310A / AT 2026fgk: COLIBRÍ photometric evidence of the emerging supernova
  23. GRB 260310A: OSIRIS+/GTC spectroscopic detection of the associated BL-Ic, SN 2026fgk
  24. The EP-WXT trigger 01709259173 is likely a flaring star
  25. GRB 260310A / AT2026fgk: Late-time infrared detection with MIRAGE on the MDM 1.3m telescope
  26. IPN triangulation of GRB 260320A
  27. EP260324a: ZTF discovery of the optical counterpart ZTF26aapviim/AT2026hir
  28. GRB 260310A / AT2026fgk: R- and I-band observations with the PKU 60 cm optical telescope
  29. GRB 260326A: Fermi GBM Detection
  30. EP260321a: JinShan near-infrared observations
  31. GRB 260325A: Fermi GBM Final Localization
  32. GRB 260326A: Fermi GBM Final Real-time Localization
  33. EP260321a: Upper limits from a neutrino search with IceCube
  34. Fermi Gamma-ray Burst Monitor trigger 796145512/260325647 is not a GRB
  35. GRB 260310A/AT2026fgk: Kilonova-Catcher late optical afterglow detection at about 15 days post trigger time
  36. IPN triangulation of GRB 260316B
  37. EP260321a: J-band observations by the SYSU 80 cm infrared telescope
  38. GRID detection of GRB 260320A
  39. EP260321a: Gemini-South confirmation of a supernova (duplicate submission)
  40. EP260321a: Gemini-South confirmation of a supernova
  41. Fermi Gamma-ray Burst Monitor trigger 796060650/260324665 is not a GRB
  42. EP260321a: VLT/FORS2 spectroscopy confirmation of an associated type Ic-BL supernova SN 2026gzf
  43. GRB 260310A: LBT optical observations
  44. EP260321A: Mondy optical observations
  45. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limits at the FXT positions
  46. EP-WXT trigger 01709259112: confirmation of a stellar flare by BOOTES-5 & BOOTES-7
  47. GRB 260316B: CALET Gamma-Ray Burst Monitor detection
  48. The EP-WXT trigger 01709259112 is likely a flaring star
  49. Fermi GRB 260323A: Global MASTER-Net observations report
  50. GRB 260323A: Fermi GBM Final Real-time Localization
  51. GRB260310A: Palomar 60-inch photometry of an extremely bright late-time afterglow with a temporal break at 8 days
  52. GRB 260310A/AT2026fgk: Detection of temporal steepening in Einstein Probe X-ray data
  53. GRB 260322A: Fermi GBM Final Localization
  54. GRB 260320A: Glowbug gamma-ray detection
  55. EP260321a / AT2026gzf: VLT/X-shooter detection of supernova-like spectral features at z = 0.0344
  56. EP260321a: COLIBRÍ further optical observations and brightening
  57. Fermi Gamma-ray Burst Monitor trigger 795918973/260323025 is not a GRB
  58. EP260321a: Continued brightening from Kinder follow-up of the emerging supernova candidate
  59. EP260214b: ATCA 6 GHz detection
  60. EP260321a: Early TRT rising followed by JinShan decaying and then re-rising
  61. GRB 260321A: EP-FXT follow-up observation
  62. The EP-WXT trigger 01709259045 is likely a flaring star
  63. EP260321a: ZTF and Rubin detections of the candidate optical counterpart to EP260321a
  64. EP260321a: GOTO detection of blue variable source
  65. EP260321a: VLT imaging and spectroscopy show the variable source to be at z = 0.0343
  66. EP260321a: further Kinder optical observations
  67. GRB 260321A: SVOM/VT optical upper limits
  68. EP260321a: Las Cumbres upper limit
  69. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  70. GRB 260320A: Insight-HXMT/HE detection
  71. EP260321a: COLIBRÍ optical upper limit on any supernova shock breakout emission
  72. EP260321a: refined analysis of the EP-WXT and EP-FXT observations, implying a possible supernova shock breakout candidate
  73. EP260321a: SVOM/VT optical upper limit
  74. GRB 260310A: continued optical observation at Mondy
  75. Fermi GBM Sub-Threshold Detection of GRB 260321A
  76. GRB 260321A: SVOM detection of a burst
  77. EP260321a: Kinder observations detect a blue variable star and set limits on a source from the z =0.034 galaxy within the error circle
  78. EP260321a: Global MASTER-Net observations report
  79. EP260321a: Einstein Probe detection of an X-ray transient
  80. GRB 260310A / AT2026fgk: ABObservatory and NOCTIS new optical observations
  81. GRB 260318A: Glowbug gamma-ray detection
  82. GRB 260310A / AT 2026fgk: KAIT optical observations
  83. GRB 260320A: NuSTAR detection of prompt emission
  84. GRB 260310A / AT2026fgk: NuSTAR follow-up detection
  85. EP-WXT trigger 01709258989: KAIT confirmation of a stellar flare
  86. GRB 260310A / AT 2026fgk: FTW optical and NIR observations show no rebrightening
  87. GRB 260310A: no evidence of re-brightening up to 9.6 days in optical observation at Mondy
  88. GRB 260310A / AT 2026fgk: COLIBRÍ evidence of a late rebrightening
  89. GRB 260310A/AT2026fgk: LBT near-infrared observations
  90. NOEMA Detection of GRB 260310A / AT 2026fgk
  91. EP-WXT trigger 01709258989: confirmation of a stellar flare by BOOTES-7
  92. GRB 260318A: SVOM/GRM observation
  93. The EP-WXT trigger 01709258989 is likely a flaring star
  94. GRB 260310A: classification as long GRB based on Eiso, Ep, and T_90
  95. GRB 260318A: GECAM-B observation
  96. GRB260310A/AT2026fgk: Further optical observation from 1.3m DFOT
  97. Fermi GRB 260318A: Global MASTER-Net observations report
  98. GRB 260318A: Fermi GBM Final Real-time Localization
  99. IceCube-260315A: No Candidate Transients from the Zwicky Transient Facility
  100. Fermi Gamma-ray Burst Monitor trigger 795096033/260312500 (GRB 260313A) is unlikely to be a GRB

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