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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. EP260327a: SVOM/VT optical upper limits
  2. SMA Detection of GRB 260310A / AT 2026fgk
  3. GRB 260307B: ATCA Radio Upper Limits
  4. EP260327a: WINTER J-band upper limit
  5. EP260327a: COLIBRÍ optical upper limits
  6. GRB 260327A: AstroSat CZTI detection of a long burst
  7. EP260327a: Gemini-North optical upper limits
  8. EP260324a: GROWTH-India Telescope optical observation
  9. EP260327a: Global MASTER-Net observations report
  10. EP260327a: Einstein Probe detection of an X-ray transient
  11. GRB 260310A / AT 2026fgk: COLIBRÍ photometric evidence of the emerging supernova
  12. GRB 260310A: OSIRIS+/GTC spectroscopic detection of the associated BL-Ic, SN 2026fgk
  13. The EP-WXT trigger 01709259173 is likely a flaring star
  14. GRB 260310A / AT2026fgk: Late-time infrared detection with MIRAGE on the MDM 1.3m telescope
  15. IPN triangulation of GRB 260320A
  16. EP260324a: ZTF discovery of the optical counterpart ZTF26aapviim/AT2026hir
  17. GRB 260310A / AT2026fgk: R- and I-band observations with the PKU 60 cm optical telescope
  18. GRB 260326A: Fermi GBM Detection
  19. EP260321a: JinShan near-infrared observations
  20. GRB 260325A: Fermi GBM Final Localization
  21. GRB 260326A: Fermi GBM Final Real-time Localization
  22. EP260321a: Upper limits from a neutrino search with IceCube
  23. Fermi Gamma-ray Burst Monitor trigger 796145512/260325647 is not a GRB
  24. GRB 260310A/AT2026fgk: Kilonova-Catcher late optical afterglow detection at about 15 days post trigger time
  25. IPN triangulation of GRB 260316B
  26. EP260321a: J-band observations by the SYSU 80 cm infrared telescope
  27. GRID detection of GRB 260320A
  28. EP260321a: Gemini-South confirmation of a supernova (duplicate submission)
  29. EP260321a: Gemini-South confirmation of a supernova
  30. Fermi Gamma-ray Burst Monitor trigger 796060650/260324665 is not a GRB
  31. EP260321a: VLT/FORS2 spectroscopy confirmation of an associated type Ic-BL supernova SN 2026gzf
  32. GRB 260310A: LBT optical observations
  33. EP260321A: Mondy optical observations
  34. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limits at the FXT positions
  35. EP-WXT trigger 01709259112: confirmation of a stellar flare by BOOTES-5 & BOOTES-7
  36. GRB 260316B: CALET Gamma-Ray Burst Monitor detection
  37. The EP-WXT trigger 01709259112 is likely a flaring star
  38. Fermi GRB 260323A: Global MASTER-Net observations report
  39. GRB 260323A: Fermi GBM Final Real-time Localization
  40. GRB260310A: Palomar 60-inch photometry of an extremely bright late-time afterglow with a temporal break at 8 days
  41. GRB 260310A/AT2026fgk: Detection of temporal steepening in Einstein Probe X-ray data
  42. GRB 260322A: Fermi GBM Final Localization
  43. GRB 260320A: Glowbug gamma-ray detection
  44. EP260321a / AT2026gzf: VLT/X-shooter detection of supernova-like spectral features at z = 0.0344
  45. EP260321a: COLIBRÍ further optical observations and brightening
  46. Fermi Gamma-ray Burst Monitor trigger 795918973/260323025 is not a GRB
  47. EP260321a: Continued brightening from Kinder follow-up of the emerging supernova candidate
  48. EP260214b: ATCA 6 GHz detection
  49. EP260321a: Early TRT rising followed by JinShan decaying and then re-rising
  50. GRB 260321A: EP-FXT follow-up observation
  51. The EP-WXT trigger 01709259045 is likely a flaring star
  52. EP260321a: ZTF and Rubin detections of the candidate optical counterpart to EP260321a
  53. EP260321a: GOTO detection of blue variable source
  54. EP260321a: VLT imaging and spectroscopy show the variable source to be at z = 0.0343
  55. EP260321a: further Kinder optical observations
  56. GRB 260321A: SVOM/VT optical upper limits
  57. EP260321a: Las Cumbres upper limit
  58. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  59. GRB 260320A: Insight-HXMT/HE detection
  60. EP260321a: COLIBRÍ optical upper limit on any supernova shock breakout emission
  61. EP260321a: refined analysis of the EP-WXT and EP-FXT observations, implying a possible supernova shock breakout candidate
  62. EP260321a: SVOM/VT optical upper limit
  63. GRB 260310A: continued optical observation at Mondy
  64. Fermi GBM Sub-Threshold Detection of GRB 260321A
  65. GRB 260321A: SVOM detection of a burst
  66. EP260321a: Kinder observations detect a blue variable star and set limits on a source from the z =0.034 galaxy within the error circle
  67. EP260321a: Global MASTER-Net observations report
  68. EP260321a: Einstein Probe detection of an X-ray transient
  69. GRB 260310A / AT2026fgk: ABObservatory and NOCTIS new optical observations
  70. GRB 260318A: Glowbug gamma-ray detection
  71. GRB 260310A / AT 2026fgk: KAIT optical observations
  72. GRB 260320A: NuSTAR detection of prompt emission
  73. GRB 260310A / AT2026fgk: NuSTAR follow-up detection
  74. EP-WXT trigger 01709258989: KAIT confirmation of a stellar flare
  75. GRB 260310A / AT 2026fgk: FTW optical and NIR observations show no rebrightening
  76. GRB 260310A: no evidence of re-brightening up to 9.6 days in optical observation at Mondy
  77. GRB 260310A / AT 2026fgk: COLIBRÍ evidence of a late rebrightening
  78. GRB 260310A/AT2026fgk: LBT near-infrared observations
  79. NOEMA Detection of GRB 260310A / AT 2026fgk
  80. EP-WXT trigger 01709258989: confirmation of a stellar flare by BOOTES-7
  81. GRB 260318A: SVOM/GRM observation
  82. The EP-WXT trigger 01709258989 is likely a flaring star
  83. GRB 260310A: classification as long GRB based on Eiso, Ep, and T_90
  84. GRB 260318A: GECAM-B observation
  85. GRB260310A/AT2026fgk: Further optical observation from 1.3m DFOT
  86. Fermi GRB 260318A: Global MASTER-Net observations report
  87. GRB 260318A: Fermi GBM Final Real-time Localization
  88. IceCube-260315A: No Candidate Transients from the Zwicky Transient Facility
  89. Fermi Gamma-ray Burst Monitor trigger 795096033/260312500 (GRB 260313A) is unlikely to be a GRB
  90. GRB 260316A / EP260316a: COLIBRÍ optical followup of counterpart candidate
  91. GRB 260310A / AT 2026fgk: radio detection with the VLA
  92. GRB 260310A / AT2026fgk: SVOM/VT optical observations
  93. GRB 260310A / AT2026fgk: LCO optical observations
  94. IceCube-260315A/AT2026fpm: EP-FXT follow-up observation
  95. GRB 260317A: Fermi GBM Final Localization
  96. GRB 260316B: GECAM-B observation
  97. GRB 260316B: SVOM/GRM observation
  98. EP260316a / GRB 260316A: SVOM/VT optical upper limits
  99. EP260316a: COLIBRÍ faint optical counterpart candidate
  100. Fermi-LAT Gamma-ray Observations of IceCube-260315A

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