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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 260503A: Fermi GBM Final Real-time Localization
  2. SVOM/GRM observation of a bright burst from SGR 1E1841-045
  3. GRB 260502A: GECAM-B observation of a short burst
  4. IPN triangulation of a bright burst from SGR 1E1841-045
  5. GRB 260502A: Fermi GBM Final Localization
  6. The EP-WXT trigger 01709261576 is likely a flaring star
  7. GRB 260429B / EP260429a: EP-FXT follow-up observation
  8. EP260502a: BOOTES-7 observations of a fading catalogued source close to the X-ray position
  9. GRB 260429B / EP260429a: AstroSat CZTI detection
  10. GRB EP260502a: BOOTES-7: early optical upper limit
  11. EP260502a: Las Cumbres upper limit
  12. EP260502a: Einstein Probe detection of an X-ray transient
  13. GRB 260429A: SVOM/GRM observation of a short burst
  14. SN 2026kid: Optical follow-up with small-aperture telescopes in Spain and China
  15. EP260429a: Global MASTER-Net observations report
  16. EP260430a: refined analysis of the EP-WXT and follow-up EP-FXT observations
  17. GRB 260424B: AstroSat CZTI detection
  18. GRB 260429B / EP260429a: COLIBRÍ optical upper limit
  19. EP260429a: LCO optical upper limits
  20. EP260430a: LCO optical upper limits
  21. GRB 260430A / EP260430a: COLIBRÍ optical upper limit
  22. GRB 260429A: Fermi GBM Detection
  23. Fermi GRB 260429A: Global MASTER-Net observations report
  24. EP260430a: Global MASTER-Net observations report
  25. EP260430a: Einstein Probe detection of an X-ray transient
  26. EP260429a: EP-WXT detection of a fast X-ray transient
  27. GRB 260429A: Fermi GBM Final Real-time Localization
  28. GRB 260428A: SVOM/GRM observation of a possible short burst with extended emission
  29. GRB 260428A: GECAM-B detection of a possible long duration Type I burst
  30. IceCube-260425A: Upper limits from a search for additional neutrino events in IceCube
  31. GRB 260428A: AstroSat CZTI detection
  32. Fermi GRB 260428A: Global MASTER-Net observations report
  33. EP260416a: Mondy and Terskol optical upper limits
  34. GRB 260424B: Glowbug gamma-ray detection of a short burst
  35. GRB 260424B: COLIBRÍ optical upper limit
  36. Konus-Wind detection of GRB 260424B
  37. GRB 260428A: Fermi GBM Final Real-time Localization
  38. Fermi-LAT Gamma-ray Observations of IceCube-260425A
  39. GRB 260424C: Fermi GBM Final Localization
  40. EP260321a/SN 2026gzf: spectroscopy at Mondy observatory
  41. IPN triangulation of GRB 260424B (short)
  42. GRB 260424B: SVOM/GRM detection of a short burst
  43. IceCube-260425A - IceCube observation of a high-energy neutrino candidate track-like event
  44. GRB 260305A: likely detection by Fermi-LAT and the LAT gamma-ray position
  45. IceCube Alert 260425A: Global MASTER-Net observations report
  46. Fermi trigger No 798737427: Global MASTER-Net observations report
  47. GRB 260401A: cubesat Avion detection
  48. GRB 260424A: AstroSat CZTI detection of a long burst
  49. EP260321a: Upper limits from ATCA radio observations
  50. GRB 260421B: Kilonova-Catcher optical afterglow detection
  51. GRB 260421B: Insight-HXMT/HE detection
  52. The EP-WXT trigger 01709258652: Mondy optical observations
  53. GRB 250328A: VLT host galaxy discovery and redshift z = 1.250
  54. EP260416a: Mondy optical observations
  55. GRB 260421B: SVOM/ECLAIRs refined analysis
  56. GRB 260421B: 3.6m DOT optical observation
  57. EP260416a: ZTSh R band observations
  58. EP-WXT trigger 01709260362: FRAM-ORM optical observations confirm flaring star G 151-9
  59. IceCube-Cascade 260418A: Upper limits from a search for additional neutrino events in IceCube
  60. EP250512a / GRB 250512B: VLT/X-shooter host galaxy identification and redshift z = 1.773
  61. GRB 250530A: VLT/X-shooter host galaxy redshift z = 1.486
  62. GRB 260419A: AstroSat CZTI detection
  63. GRB 260421B: SVOM/GRM observation
  64. GRB260421B: J band upper limit by SYSU 80cm infrared telescope
  65. GRB 260421B: EP-FXT follow-up observation
  66. The EP-WXT trigger 01709260362 is likely a flaring star
  67. GOTO26djh/AT2026jpw: ATCA radio detection
  68. GRB 260421B: J-band upper limit with WINTER
  69. GRB 260421B: LCO optical counterpart detection
  70. GRB 260421B: Fermi GBM Observation
  71. Fermi Gamma-ray Burst Monitor trigger 798482368/260421694 is not a GRB
  72. GRB 260421A: AstroSat CZTI detection
  73. GOTO26djh/AT2026jpw: radio detection at 15GHz
  74. GRB 260412A: SVOM/ECLAIRs refined analysis
  75. GRB 260421B: SVOM/VT optical observations
  76. EP260416a: J band upper limit by SYSU 80cm infrared telescope
  77. GRB 260310A: Late-time Chandra X-ray Detection
  78. GRB 260418A: Insight-HXMT/HE detection
  79. EP260416a: 1.3m DFOT optical observation
  80. GRB 260415A: CALET Gamma-Ray Burst Monitor detection
  81. GRB 260415B: CALET Gamma-Ray Burst Monitor detection
  82. Fermi GRB 260421C: Global MASTER-Net observations report
  83. GRB 260421C: Fermi GBM Final Real-time Localization
  84. GRB 260421B: VLT/X-shooter spectroscopic redshift z = 2.115
  85. Fermi GRB 260421B: Global MASTER-Net observations report
  86. GRB 260421B: BOOTES-7 early optical afterglow detection
  87. GRB 260421B: LCO optical afterglow confirmation
  88. GRB 260421B: SVOM/COLIBRÍ (FM-GFT) optical detection of a candidate counterpart
  89. GRB 260421B: TRT optical counterpart detection
  90. GRB 260421B: SVOM detection of a long burst
  91. GRB 260421B: BALROG localization (Fermi Trigger 798437606 / GRB 260421176)
  92. GRB 260421B: Fermi GBM Final Real-time Localization
  93. Fermi GRB 260421A: Global MASTER-Net observations report
  94. GRB 260421A: Fermi GBM Final Real-time Localization
  95. EP260321a: VLA radio follow-up
  96. GRB 260412A: LCOGT Optical Upper Limits
  97. The EP-WXT trigger 01709260314 is likely a flaring star
  98. EP260416a: Optical follow-up observations with Kinder
  99. GOTO26djh/AT2026jpw: CrAO and Mondy optical observations of the transient
  100. EP-WXT trigger 01709260303: KAIT optical observations

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