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

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