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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. Fermi GRB 260504A: Global MASTER-Net observations report
  2. GRB 260504A: Fermi GBM Final Real-time Localization
  3. GRB 260503A: Fermi GBM Final Real-time Localization
  4. SVOM/GRM observation of a bright burst from SGR 1E1841-045
  5. GRB 260502A: GECAM-B observation of a short burst
  6. IPN triangulation of a bright burst from SGR 1E1841-045
  7. GRB 260502A: Fermi GBM Final Localization
  8. The EP-WXT trigger 01709261576 is likely a flaring star
  9. GRB 260429B / EP260429a: EP-FXT follow-up observation
  10. EP260502a: BOOTES-7 observations of a fading catalogued source close to the X-ray position
  11. GRB 260429B / EP260429a: AstroSat CZTI detection
  12. EP260502a: BOOTES-7: early optical upper limit
  13. EP260502a: Las Cumbres upper limit
  14. EP260502a: Einstein Probe detection of an X-ray transient
  15. GRB 260429A: SVOM/GRM observation of a short burst
  16. SN 2026kid: Optical follow-up with small-aperture telescopes in Spain and China
  17. EP260429a: Global MASTER-Net observations report
  18. EP260430a: refined analysis of the EP-WXT and follow-up EP-FXT observations
  19. GRB 260424B: AstroSat CZTI detection
  20. GRB 260429B / EP260429a: COLIBRÍ optical upper limit
  21. EP260429a: LCO optical upper limits
  22. EP260430a: LCO optical upper limits
  23. GRB 260430A / EP260430a: COLIBRÍ optical upper limit
  24. GRB 260429A: Fermi GBM Detection
  25. Fermi GRB 260429A: Global MASTER-Net observations report
  26. EP260430a: Global MASTER-Net observations report
  27. EP260430a: Einstein Probe detection of an X-ray transient
  28. EP260429a: EP-WXT detection of a fast X-ray transient
  29. GRB 260429A: Fermi GBM Final Real-time Localization
  30. GRB 260428A: SVOM/GRM observation of a possible short burst with extended emission
  31. GRB 260428A: GECAM-B detection of a possible long duration Type I burst
  32. IceCube-260425A: Upper limits from a search for additional neutrino events in IceCube
  33. GRB 260428A: AstroSat CZTI detection
  34. Fermi GRB 260428A: Global MASTER-Net observations report
  35. EP260416a: Mondy and Terskol optical upper limits
  36. GRB 260424B: Glowbug gamma-ray detection of a short burst
  37. GRB 260424B: COLIBRÍ optical upper limit
  38. Konus-Wind detection of GRB 260424B
  39. GRB 260428A: Fermi GBM Final Real-time Localization
  40. Fermi-LAT Gamma-ray Observations of IceCube-260425A
  41. GRB 260424C: Fermi GBM Final Localization
  42. EP260321a/SN 2026gzf: spectroscopy at Mondy observatory
  43. IPN triangulation of GRB 260424B (short)
  44. GRB 260424B: SVOM/GRM detection of a short burst
  45. IceCube-260425A - IceCube observation of a high-energy neutrino candidate track-like event
  46. GRB 260305A: likely detection by Fermi-LAT and the LAT gamma-ray position
  47. IceCube Alert 260425A: Global MASTER-Net observations report
  48. Fermi trigger No 798737427: Global MASTER-Net observations report
  49. GRB 260401A: cubesat Avion detection
  50. GRB 260424A: AstroSat CZTI detection of a long burst
  51. EP260321a: Upper limits from ATCA radio observations
  52. GRB 260421B: Kilonova-Catcher optical afterglow detection
  53. GRB 260421B: Insight-HXMT/HE detection
  54. The EP-WXT trigger 01709258652: Mondy optical observations
  55. GRB 250328A: VLT host galaxy discovery and redshift z = 1.250
  56. EP260416a: Mondy optical observations
  57. GRB 260421B: SVOM/ECLAIRs refined analysis
  58. GRB 260421B: 3.6m DOT optical observation
  59. EP260416a: ZTSh R band observations
  60. EP-WXT trigger 01709260362: FRAM-ORM optical observations confirm flaring star G 151-9
  61. IceCube-Cascade 260418A: Upper limits from a search for additional neutrino events in IceCube
  62. EP250512a / GRB 250512B: VLT/X-shooter host galaxy identification and redshift z = 1.773
  63. GRB 250530A: VLT/X-shooter host galaxy redshift z = 1.486
  64. GRB 260419A: AstroSat CZTI detection
  65. GRB 260421B: SVOM/GRM observation
  66. GRB260421B: J band upper limit by SYSU 80cm infrared telescope
  67. GRB 260421B: EP-FXT follow-up observation
  68. The EP-WXT trigger 01709260362 is likely a flaring star
  69. GOTO26djh/AT2026jpw: ATCA radio detection
  70. GRB 260421B: J-band upper limit with WINTER
  71. GRB 260421B: LCO optical counterpart detection
  72. GRB 260421B: Fermi GBM Observation
  73. Fermi Gamma-ray Burst Monitor trigger 798482368/260421694 is not a GRB
  74. GRB 260421A: AstroSat CZTI detection
  75. GOTO26djh/AT2026jpw: radio detection at 15GHz
  76. GRB 260412A: SVOM/ECLAIRs refined analysis
  77. GRB 260421B: SVOM/VT optical observations
  78. EP260416a: J band upper limit by SYSU 80cm infrared telescope
  79. GRB 260310A: Late-time Chandra X-ray Detection
  80. GRB 260418A: Insight-HXMT/HE detection
  81. EP260416a: 1.3m DFOT optical observation
  82. GRB 260415A: CALET Gamma-Ray Burst Monitor detection
  83. GRB 260415B: CALET Gamma-Ray Burst Monitor detection
  84. Fermi GRB 260421C: Global MASTER-Net observations report
  85. GRB 260421C: Fermi GBM Final Real-time Localization
  86. GRB 260421B: VLT/X-shooter spectroscopic redshift z = 2.115
  87. Fermi GRB 260421B: Global MASTER-Net observations report
  88. GRB 260421B: BOOTES-7 early optical afterglow detection
  89. GRB 260421B: LCO optical afterglow confirmation
  90. GRB 260421B: SVOM/COLIBRÍ (FM-GFT) optical detection of a candidate counterpart
  91. GRB 260421B: TRT optical counterpart detection
  92. GRB 260421B: SVOM detection of a long burst
  93. GRB 260421B: BALROG localization (Fermi Trigger 798437606 / GRB 260421176)
  94. GRB 260421B: Fermi GBM Final Real-time Localization
  95. Fermi GRB 260421A: Global MASTER-Net observations report
  96. GRB 260421A: Fermi GBM Final Real-time Localization
  97. EP260321a: VLA radio follow-up
  98. GRB 260412A: LCOGT Optical Upper Limits
  99. The EP-WXT trigger 01709260314 is likely a flaring star
  100. EP260416a: Optical follow-up observations with Kinder

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