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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. EP260329b: Einstein Probe detection of an X-ray transient
  2. EP260329a: Einstein Probe detection of an X-ray transient
  3. EP-WXT trigger 01709259209: TRT optical counterpart detection
  4. The EP-WXT trigger 01709259209 (EP260329b?): Las Cumbres discovery of the optical counterpart
  5. GRID detection of GRB 260326A
  6. GRB 260310A: Gemini-North Spectral Confirmation of Supernova Features
  7. EP260327a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  8. EP260327a: SVOM/VT optical upper limits
  9. SMA Detection of GRB 260310A / AT 2026fgk
  10. GRB 260307B: ATCA Radio Upper Limits
  11. EP260327a: WINTER J-band upper limit
  12. EP260327a: COLIBRÍ optical upper limits
  13. GRB 260327A: AstroSat CZTI detection of a long burst
  14. EP260327a: Gemini-North optical upper limits
  15. EP260324a: GROWTH-India Telescope optical observation
  16. EP260327a: Global MASTER-Net observations report
  17. EP260327a: Einstein Probe detection of an X-ray transient
  18. GRB 260310A / AT 2026fgk: COLIBRÍ photometric evidence of the emerging supernova
  19. GRB 260310A: OSIRIS+/GTC spectroscopic detection of the associated BL-Ic, SN 2026fgk
  20. The EP-WXT trigger 01709259173 is likely a flaring star
  21. GRB 260310A / AT2026fgk: Late-time infrared detection with MIRAGE on the MDM 1.3m telescope
  22. IPN triangulation of GRB 260320A
  23. EP260324a: ZTF discovery of the optical counterpart ZTF26aapviim/AT2026hir
  24. GRB 260310A / AT2026fgk: R- and I-band observations with the PKU 60 cm optical telescope
  25. GRB 260326A: Fermi GBM Detection
  26. EP260321a: JinShan near-infrared observations
  27. GRB 260325A: Fermi GBM Final Localization
  28. GRB 260326A: Fermi GBM Final Real-time Localization
  29. EP260321a: Upper limits from a neutrino search with IceCube
  30. Fermi Gamma-ray Burst Monitor trigger 796145512/260325647 is not a GRB
  31. GRB 260310A/AT2026fgk: Kilonova-Catcher late optical afterglow detection at about 15 days post trigger time
  32. IPN triangulation of GRB 260316B
  33. EP260321a: J-band observations by the SYSU 80 cm infrared telescope
  34. GRID detection of GRB 260320A
  35. EP260321a: Gemini-South confirmation of a supernova (duplicate submission)
  36. EP260321a: Gemini-South confirmation of a supernova
  37. Fermi Gamma-ray Burst Monitor trigger 796060650/260324665 is not a GRB
  38. EP260321a: VLT/FORS2 spectroscopy confirmation of an associated type Ic-BL supernova SN 2026gzf
  39. GRB 260310A: LBT optical observations
  40. EP260321A: Mondy optical observations
  41. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limits at the FXT positions
  42. EP-WXT trigger 01709259112: confirmation of a stellar flare by BOOTES-5 & BOOTES-7
  43. GRB 260316B: CALET Gamma-Ray Burst Monitor detection
  44. The EP-WXT trigger 01709259112 is likely a flaring star
  45. Fermi GRB 260323A: Global MASTER-Net observations report
  46. GRB 260323A: Fermi GBM Final Real-time Localization
  47. GRB260310A: Palomar 60-inch photometry of an extremely bright late-time afterglow with a temporal break at 8 days
  48. GRB 260310A/AT2026fgk: Detection of temporal steepening in Einstein Probe X-ray data
  49. GRB 260322A: Fermi GBM Final Localization
  50. GRB 260320A: Glowbug gamma-ray detection
  51. EP260321a / AT2026gzf: VLT/X-shooter detection of supernova-like spectral features at z = 0.0344
  52. EP260321a: COLIBRÍ further optical observations and brightening
  53. Fermi Gamma-ray Burst Monitor trigger 795918973/260323025 is not a GRB
  54. EP260321a: Continued brightening from Kinder follow-up of the emerging supernova candidate
  55. EP260214b: ATCA 6 GHz detection
  56. EP260321a: Early TRT rising followed by JinShan decaying and then re-rising
  57. GRB 260321A: EP-FXT follow-up observation
  58. The EP-WXT trigger 01709259045 is likely a flaring star
  59. EP260321a: ZTF and Rubin detections of the candidate optical counterpart to EP260321a
  60. EP260321a: GOTO detection of blue variable source
  61. EP260321a: VLT imaging and spectroscopy show the variable source to be at z = 0.0343
  62. EP260321a: further Kinder optical observations
  63. GRB 260321A: SVOM/VT optical upper limits
  64. EP260321a: Las Cumbres upper limit
  65. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  66. GRB 260320A: Insight-HXMT/HE detection
  67. EP260321a: COLIBRÍ optical upper limit on any supernova shock breakout emission
  68. EP260321a: refined analysis of the EP-WXT and EP-FXT observations, implying a possible supernova shock breakout candidate
  69. EP260321a: SVOM/VT optical upper limit
  70. GRB 260310A: continued optical observation at Mondy
  71. Fermi GBM Sub-Threshold Detection of GRB 260321A
  72. GRB 260321A: SVOM detection of a burst
  73. EP260321a: Kinder observations detect a blue variable star and set limits on a source from the z =0.034 galaxy within the error circle
  74. EP260321a: Global MASTER-Net observations report
  75. EP260321a: Einstein Probe detection of an X-ray transient
  76. GRB 260310A / AT2026fgk: ABObservatory and NOCTIS new optical observations
  77. GRB 260318A: Glowbug gamma-ray detection
  78. GRB 260310A / AT 2026fgk: KAIT optical observations
  79. GRB 260320A: NuSTAR detection of prompt emission
  80. GRB 260310A / AT2026fgk: NuSTAR follow-up detection
  81. EP-WXT trigger 01709258989: KAIT confirmation of a stellar flare
  82. GRB 260310A / AT 2026fgk: FTW optical and NIR observations show no rebrightening
  83. GRB 260310A: no evidence of re-brightening up to 9.6 days in optical observation at Mondy
  84. GRB 260310A / AT 2026fgk: COLIBRÍ evidence of a late rebrightening
  85. GRB 260310A/AT2026fgk: LBT near-infrared observations
  86. NOEMA Detection of GRB 260310A / AT 2026fgk
  87. EP-WXT trigger 01709258989: confirmation of a stellar flare by BOOTES-7
  88. GRB 260318A: SVOM/GRM observation
  89. The EP-WXT trigger 01709258989 is likely a flaring star
  90. GRB 260310A: classification as long GRB based on Eiso, Ep, and T_90
  91. GRB 260318A: GECAM-B observation
  92. GRB260310A/AT2026fgk: Further optical observation from 1.3m DFOT
  93. Fermi GRB 260318A: Global MASTER-Net observations report
  94. GRB 260318A: Fermi GBM Final Real-time Localization
  95. IceCube-260315A: No Candidate Transients from the Zwicky Transient Facility
  96. Fermi Gamma-ray Burst Monitor trigger 795096033/260312500 (GRB 260313A) is unlikely to be a GRB
  97. GRB 260316A / EP260316a: COLIBRÍ optical followup of counterpart candidate
  98. GRB 260310A / AT 2026fgk: radio detection with the VLA
  99. GRB 260310A / AT2026fgk: SVOM/VT optical observations
  100. GRB 260310A / AT2026fgk: LCO optical observations

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