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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. GRB 260504C: SVOM/GRM observation of short GRB
  2. GRB 260430B: AstroSat CZTI detection of a long burst
  3. GRB 260504B: SVOM/MXT refined analysis and potential detection
  4. GRB 260503A: SVOM/GRM observation of a GRB
  5. GRB 260310A / AT2026fgk: photometric monitoring and tentative maximum of a possible SN
  6. Konus-Wind detection of GRB 260411C
  7. GRB 260504B: REM optical/NIR observations
  8. IPN triangulation of GRB 260428A
  9. GRB 260504B: AST3-2 i-band upper limit
  10. GRB 260504B: LCO z-band upper limit
  11. SVOM GRB 260504B: MASTER-OAFA optical observations
  12. GRB 260504B: SVOM detection of a short burst
  13. Fermi GRB 260504A: Global MASTER-Net observations report
  14. GRB 260504A: Fermi GBM Final Real-time Localization
  15. GRB 260503A: Fermi GBM Final Real-time Localization
  16. SVOM/GRM observation of a bright burst from SGR 1E1841-045
  17. GRB 260502A: GECAM-B observation of a short burst
  18. IPN triangulation of a bright burst from SGR 1E1841-045
  19. GRB 260502A: Fermi GBM Final Localization
  20. GRB 260429B / EP260429a: AstroSat CZTI detection
  21. EP260502a: Las Cumbres upper limit
  22. EP260502a: Einstein Probe detection of an X-ray transient
  23. GRB 260429A: SVOM/GRM observation of a short burst
  24. EP260429a: Global MASTER-Net observations report
  25. GRB 260424B: AstroSat CZTI detection
  26. EP260429a: LCO optical upper limits
  27. GRB 260430A / EP260430a: COLIBRÍ optical upper limit
  28. GRB 260429A: Fermi GBM Detection
  29. Fermi GRB 260429A: Global MASTER-Net observations report
  30. EP260430a: Global MASTER-Net observations report
  31. EP260430a: Einstein Probe detection of an X-ray transient
  32. EP260429a: EP-WXT detection of a fast X-ray transient
  33. GRB 260429A: Fermi GBM Final Real-time Localization
  34. GRB 260428A: SVOM/GRM observation of a possible short burst with extended emission
  35. GRB 260428A: GECAM-B detection of a possible long duration Type I burst
  36. Fermi GRB 260428A: Global MASTER-Net observations report
  37. GRB 260424B: Glowbug gamma-ray detection of a short burst
  38. GRB 260424B: COLIBRÍ optical upper limit
  39. Konus-Wind detection of GRB 260424B
  40. GRB 260428A: Fermi GBM Final Real-time Localization
  41. Fermi-LAT Gamma-ray Observations of IceCube-260425A
  42. GRB 260424C: Fermi GBM Final Localization
  43. IPN triangulation of GRB 260424B (short)
  44. IceCube-260425A - IceCube observation of a high-energy neutrino candidate track-like event
  45. IceCube Alert 260425A: Global MASTER-Net observations report
  46. Fermi trigger No 798737427: Global MASTER-Net observations report
  47. GRB 260424A: AstroSat CZTI detection of a long burst
  48. GRB 260421B: Insight-HXMT/HE detection
  49. The EP-WXT trigger 01709258652: Mondy optical observations
  50. GRB 260421B: 3.6m DOT optical observation
  51. EP260416a: ZTSh R band observations
  52. EP-WXT trigger 01709260362: FRAM-ORM optical observations confirm flaring star G 151-9
  53. EP250512a / GRB 250512B: VLT/X-shooter host galaxy identification and redshift z = 1.773
  54. GRB 250530A: VLT/X-shooter host galaxy redshift z = 1.486
  55. GRB 260419A: AstroSat CZTI detection
  56. GRB 260421B: SVOM/GRM observation
  57. The EP-WXT trigger 01709260362 is likely a flaring star
  58. GOTO26djh/AT2026jpw: ATCA radio detection
  59. GRB 260421B: J-band upper limit with WINTER
  60. GRB 260421B: LCO optical counterpart detection
  61. Fermi Gamma-ray Burst Monitor trigger 798482368/260421694 is not a GRB
  62. GOTO26djh/AT2026jpw: radio detection at 15GHz
  63. EP260416a: J band upper limit by SYSU 80cm infrared telescope
  64. GRB 260418A: Insight-HXMT/HE detection
  65. GRB 260415A: CALET Gamma-Ray Burst Monitor detection
  66. GRB 260415B: CALET Gamma-Ray Burst Monitor detection
  67. Fermi GRB 260421C: Global MASTER-Net observations report
  68. GRB 260421B: VLT/X-shooter spectroscopic redshift z = 2.115
  69. Fermi GRB 260421B: Global MASTER-Net observations report
  70. GRB 260421B: BOOTES-7 early optical afterglow detection
  71. GRB 260421B: LCO optical afterglow confirmation
  72. GRB 260421B: TRT optical counterpart detection
  73. GRB 260421B: Fermi GBM Final Real-time Localization
  74. Fermi GRB 260421A: Global MASTER-Net observations report
  75. GRB 260421A: Fermi GBM Final Real-time Localization
  76. EP260416a: Optical follow-up observations with Kinder
  77. GOTO26djh/AT2026jpw: CrAO and Mondy optical observations of the transient
  78. EP-WXT trigger 01709260303: KAIT optical observations
  79. EP260416a: 1.5m OSN and 2.2m CAHA optical monitoring
  80. GRB 260417A: SVOM/GRM observation
  81. EP260321A/AT2026gzf: Optical observation from 1.3m DFOT
  82. GRB 260419A: Fermi GBM Final Real-time Localization
  83. EP260417b: GROWTH-India Telescope optical upper limit
  84. GRB 260418B: Fermi GBM Final Real-time Localization
  85. EP260417a: Global MASTER-Net observations report
  86. EP260417a/GRB 260417A: refined analysis of the EP-WXT and follow-up EP-FXT observations
  87. EP260416a: NOT tentative spectroscopic redshift of z =1.909
  88. Fermi GRB 260417A: Global MASTER-Net observations report
  89. Konus-Wind detection of GRB 260411B
  90. GRB 260417B: Fermi GBM Final Real-time Localization
  91. IPN triangulation of GRB 260411B
  92. EP260416a: LCO observations confirm end of flaring phase
  93. EP260324a / AT2026hir: Further multiband optical follow-up with the PKU 60cm Telescope
  94. EP260417a: Einstein Probe detection of an X-ray transient
  95. EP260417b: Einstein Probe detection of a fast X-ray transient
  96. GRB 260414A: Insight-HXMT/HE detection
  97. EP260416a: COLIBRÍ confirmation of the optical rebrightening
  98. EP260416a: WFST optical observations and rebrightening
  99. GOTO26djh/AT2026jpw: ZTSh R,I bands observations of the transient
  100. GOTO26djh/AT2026jpw: SVOM/VT optical observation

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