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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"

28036 results found.

  1. EP260209a: Global MASTER-Net observations report
  2. GRB 260208A: LCO detection of the optical counterpart
  3. EP260209a: Einstein Probe detection of a fast X-ray transient
  4. EP260210a: Optical upper limits with Kinder observations
  5. GRB 260210A: Glowbug gamma-ray detection
  6. GRB 260208C: AstroSat CZTI detection
  7. EP260210a: COLIBRÍ optical upper limit
  8. EP260210a: SVOM/C-GFT upper limit
  9. EP260210a: Einstein Probe detection of an X-ray transient
  10. GRB 260207B: AstroSat CZTI detection
  11. GRB 260208C: SVOM/GRM observation
  12. GRB 260204A: Swift-XRT afterglow detection
  13. GRB 260208B: AstroSat CZTI detection of a bright long burst
  14. GRB260208A: Liverpool Telescope optical follow-up observations
  15. GRB 260208A: Glowbug gamma-ray detection
  16. GRB 260208A: NuSTAR detection of prompt emission
  17. GRB 260208A: Fermi GBM Observation
  18. Fermi GRB 260209A: Global MASTER-Net observations report
  19. GRB 260208B: Swift-XRT observations
  20. GRB 260131A/B: continued Mondy optical observations
  21. GRB 260204A: Swift/UVOT Upper Limits
  22. GRB 260208B: COLIBRÍ optical observations
  23. GRB 260208A: Mondy optical observations
  24. GRB 260208A: 1.3m DFOT optical detection
  25. GRB 260208A: COLIBRÍ optical observations
  26. GRB 260208B: EP-FXT observation
  27. Fermi GRB 260208C: Global MASTER-Net observations report
  28. GRB 260208B: SVOM/VT optical candidate
  29. GRB 260208A: GECAM-B observation of a bright burst
  30. GRB 260208A: Zwicky Transient Facility Follow-Up of a Fermi GRB (Trigger 792220053)
  31. GRB 260208A: SVOM/VT optical observation
  32. Fermi GRB 260208D: Global MASTER-Net observations report
  33. GRB 260208A: Swift-XRT observations
  34. GRB 260208B: SVOM/GRM observation of a bright burst
  35. GRB 260208B: Fermi GBM Detection
  36. LAT GRB 260208B: Global MASTER-Net observations report
  37. GRB 260208A : MASTER bright optical transient inside retracted Fermi error-box
  38. GRB 260208B: BALROG localization (Fermi Trigger 792237169 / GRB 260208412)
  39. Fermi GRB 260208A: Global MASTER-Net observations report
  40. GRB 260207B: Fermi GBM Detection of a Short Burst with Extended Emission
  41. GRB 260131A/B: Mondy and Terskol optical observations
  42. Fermi GRB 260207B: Global MASTER-Net observations report
  43. GRB 260206A: Swift-XRT observations
  44. Fermi trigger No 792135758: Global MASTER-Net observations report
  45. GRB 260206A (or XRB from 4U 0513-40): MAXI/GSC detection
  46. GRB 260204A: Swift-XRT observations
  47. GRB 260204A: SVOM/VT optical candidate
  48. GRB 260204A : MASTER Global robotic net optical observations
  49. Fermi GBM Sub-Threshold Detection of GRB 260204A
  50. GRB 260204A: LCO optical upper limits
  51. EP260110a: Late GTC/EMIR near-infrared observations
  52. GRB 260121A: 239Alferov CubeSat detection
  53. GRB 260131A: KAIT optical observations
  54. GRB 251230A: MeerLICHT afterglow detection
  55. GRB 260131A/B: GTC/OSIRIS+ redshift confimation
  56. GRB 260130A: Insight-HXMT/HE detection
  57. GRB 260131A/B (AT2026bwg): J-band observations by SYSU 80cm infrared telescope
  58. GRB 260131A/B (AT2026bwg): COLIBRÍ further optical observations
  59. GRB 260127A: GECAM-B observation
  60. EP260131a: Liverpool Telescope optical upper limits
  61. EP260131a: COLIBRÍ further observations
  62. EP260131a: SVOM/VT optical observation
  63. EP260131a: Xinglong optical upper limit
  64. GRB 260131A/B (AT2026bwg): COLIBRÍ optical observations and confirmation of fading
  65. GRB 260131A/B: Fermi GBM Observation
  66. EP260131a: COLIBRÍ observations of slow optical fading
  67. EP260131a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  68. EP260131a: NOT early detection of the counterpart in "rapid response mode"
  69. GRB 260131B: MAXI/GSC detection
  70. EP260131a: COLIBRÍ optical observations of the counterpart
  71. EP260131a: Las Cumbres detection of an optical counterpart
  72. GRB 260127B: AstroSat CZTI detection
  73. GRB 260130A: Fermi GBM Detection
  74. EP260131a: Einstein Probe detection of an X-ray transient
  75. GRB 260127B: Fermi GBM Detection
  76. EP260128a / GRB 260128A: COLIBRÍ optical upper limit
  77. Fermi GRB 260130A: Global MASTER-Net observations report
  78. Fermi GRB 260129A: Global MASTER-Net observations report
  79. GRB 260128B: LCO optical upper limits
  80. GRB 260128B: SVOM/COLIBRÍ (FM-GFT) optical upper limits
  81. EP260128a: J band upper limit by SYSU 80cm infrared telescope
  82. GRB 260127A: Swift-BAT refined analysis
  83. GRB 260127B: Swift-XRT observations
  84. GRB 260127A: INASAN-Kislovodsk, SAO RAS, and Terskol K-800 optical observations
  85. GRB 260128A / EP260128a: Fermi-GBM Sub-Threshold Detection
  86. EP260128a: NOT optical counterpart candidate
  87. EP260128a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  88. EP260128a: Liverpool Telescope optical observations and possible counterpart
  89. EP260128a: LCO optical upper limits
  90. EP260128a: Global MASTER-Net observations report
  91. EP260128a: Einstein Probe detection of an X-ray transient
  92. Fermi GRB 260127A: Global MASTER-Net observations report
  93. GRB 260127A: Fermi GBM Observation
  94. IceCube-260125A: Upper limits from a search for additional neutrino events in IceCube
  95. GRB 260127A: COLIBRÍ optical observations
  96. EP260126a: Seimei/TriCCS optical upper limit
  97. GRB 260127A : MITSuME Akeno optical afterglow candidate detection
  98. GRB 260127A: Swift-XRT refined Analysis
  99. GRB 260127A: SVOM/C-GFT optical observations
  100. GRB 260127A: Enhanced Swift-XRT position

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