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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 260504B: AST3-2 i-band upper limit
  2. GRB 260504B: LCO z-band upper limit
  3. SVOM GRB 260504B: MASTER-OAFA optical observations
  4. GRB 260504B: SVOM detection of a short burst
  5. Fermi GRB 260504A: Global MASTER-Net observations report
  6. GRB 260504A: Fermi GBM Final Real-time Localization
  7. GRB 260503A: Fermi GBM Final Real-time Localization
  8. SVOM/GRM observation of a bright burst from SGR 1E1841-045
  9. GRB 260502A: GECAM-B observation of a short burst
  10. IPN triangulation of a bright burst from SGR 1E1841-045
  11. GRB 260502A: Fermi GBM Final Localization
  12. The EP-WXT trigger 01709261576 is likely a flaring star
  13. GRB 260429B / EP260429a: EP-FXT follow-up observation
  14. EP260502a: BOOTES-7 observations of a fading catalogued source close to the X-ray position
  15. GRB 260429B / EP260429a: AstroSat CZTI detection
  16. EP260502a: BOOTES-7: early optical upper limit
  17. EP260502a: Las Cumbres upper limit
  18. EP260502a: Einstein Probe detection of an X-ray transient
  19. GRB 260429A: SVOM/GRM observation of a short burst
  20. SN 2026kid: Optical follow-up with small-aperture telescopes in Spain and China
  21. EP260429a: Global MASTER-Net observations report
  22. EP260430a: refined analysis of the EP-WXT and follow-up EP-FXT observations
  23. GRB 260424B: AstroSat CZTI detection
  24. GRB 260429B / EP260429a: COLIBRÍ optical upper limit
  25. EP260429a: LCO optical upper limits
  26. EP260430a: 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. IceCube-260425A: Upper limits from a search for additional neutrino events in IceCube
  37. GRB 260428A: AstroSat CZTI detection
  38. Fermi GRB 260428A: Global MASTER-Net observations report
  39. EP260416a: Mondy and Terskol optical upper limits
  40. GRB 260424B: Glowbug gamma-ray detection of a short burst
  41. GRB 260424B: COLIBRÍ optical upper limit
  42. Konus-Wind detection of GRB 260424B
  43. GRB 260428A: Fermi GBM Final Real-time Localization
  44. Fermi-LAT Gamma-ray Observations of IceCube-260425A
  45. GRB 260424C: Fermi GBM Final Localization
  46. EP260321a/SN 2026gzf: spectroscopy at Mondy observatory
  47. IPN triangulation of GRB 260424B (short)
  48. GRB 260424B: SVOM/GRM detection of a short burst
  49. IceCube-260425A - IceCube observation of a high-energy neutrino candidate track-like event
  50. GRB 260305A: likely detection by Fermi-LAT and the LAT gamma-ray position
  51. IceCube Alert 260425A: Global MASTER-Net observations report
  52. Fermi trigger No 798737427: Global MASTER-Net observations report
  53. GRB 260401A: cubesat Avion detection
  54. GRB 260424A: AstroSat CZTI detection of a long burst
  55. EP260321a: Upper limits from ATCA radio observations
  56. GRB 260421B: Kilonova-Catcher optical afterglow detection
  57. GRB 260421B: Insight-HXMT/HE detection
  58. The EP-WXT trigger 01709258652: Mondy optical observations
  59. GRB 250328A: VLT host galaxy discovery and redshift z = 1.250
  60. EP260416a: Mondy optical observations
  61. GRB 260421B: SVOM/ECLAIRs refined analysis
  62. GRB 260421B: 3.6m DOT optical observation
  63. EP260416a: ZTSh R band observations
  64. EP-WXT trigger 01709260362: FRAM-ORM optical observations confirm flaring star G 151-9
  65. IceCube-Cascade 260418A: Upper limits from a search for additional neutrino events in IceCube
  66. EP250512a / GRB 250512B: VLT/X-shooter host galaxy identification and redshift z = 1.773
  67. GRB 250530A: VLT/X-shooter host galaxy redshift z = 1.486
  68. GRB 260419A: AstroSat CZTI detection
  69. GRB 260421B: SVOM/GRM observation
  70. GRB260421B: J band upper limit by SYSU 80cm infrared telescope
  71. GRB 260421B: EP-FXT follow-up observation
  72. The EP-WXT trigger 01709260362 is likely a flaring star
  73. GOTO26djh/AT2026jpw: ATCA radio detection
  74. GRB 260421B: J-band upper limit with WINTER
  75. GRB 260421B: LCO optical counterpart detection
  76. GRB 260421B: Fermi GBM Observation
  77. Fermi Gamma-ray Burst Monitor trigger 798482368/260421694 is not a GRB
  78. GRB 260421A: AstroSat CZTI detection
  79. GOTO26djh/AT2026jpw: radio detection at 15GHz
  80. GRB 260412A: SVOM/ECLAIRs refined analysis
  81. GRB 260421B: SVOM/VT optical observations
  82. EP260416a: J band upper limit by SYSU 80cm infrared telescope
  83. GRB 260310A: Late-time Chandra X-ray Detection
  84. GRB 260418A: Insight-HXMT/HE detection
  85. EP260416a: 1.3m DFOT optical observation
  86. GRB 260415A: CALET Gamma-Ray Burst Monitor detection
  87. GRB 260415B: CALET Gamma-Ray Burst Monitor detection
  88. Fermi GRB 260421C: Global MASTER-Net observations report
  89. GRB 260421C: Fermi GBM Final Real-time Localization
  90. GRB 260421B: VLT/X-shooter spectroscopic redshift z = 2.115
  91. Fermi GRB 260421B: Global MASTER-Net observations report
  92. GRB 260421B: BOOTES-7 early optical afterglow detection
  93. GRB 260421B: LCO optical afterglow confirmation
  94. GRB 260421B: SVOM/COLIBRÍ (FM-GFT) optical detection of a candidate counterpart
  95. GRB 260421B: TRT optical counterpart detection
  96. GRB 260421B: SVOM detection of a long burst
  97. GRB 260421B: BALROG localization (Fermi Trigger 798437606 / GRB 260421176)
  98. GRB 260421B: Fermi GBM Final Real-time Localization
  99. Fermi GRB 260421A: Global MASTER-Net observations report
  100. GRB 260421A: Fermi GBM Final Real-time Localization

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