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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"

28046 results found.

  1. GRB260131A/B: 3.6m DOT Optical Observations
  2. GRB 260211A: SVOM/COLIBRÍ (FM-GFT) optical upper limits
  3. Fermi trigger No 792537871: Global MASTER-Net observations report
  4. Swift Operations Update + Community Forum (Friday, February 13 @ 10:00 AM EST)
  5. EP260209a: COLIBRÍ optical upper limit
  6. Fermi GRB 260210C: Global MASTER-Net observations report
  7. EP260209a: LCO optical upper limits
  8. EP260210a: Global MASTER-Net observations report
  9. EP260210a: refined analysis of the EP-FXT observation
  10. EP260209a: Global MASTER-Net observations report
  11. GRB 260208A: LCO detection of the optical counterpart
  12. EP260209a: Einstein Probe detection of a fast X-ray transient
  13. EP260210a: Optical upper limits with Kinder observations
  14. GRB 260210A: Glowbug gamma-ray detection
  15. GRB 260208C: AstroSat CZTI detection
  16. EP260210a: COLIBRÍ optical upper limit
  17. EP260210a: SVOM/C-GFT upper limit
  18. EP260210a: Einstein Probe detection of an X-ray transient
  19. GRB 260207B: AstroSat CZTI detection
  20. GRB 260208C: SVOM/GRM observation
  21. GRB 260204A: Swift-XRT afterglow detection
  22. GRB 260208B: AstroSat CZTI detection of a bright long burst
  23. GRB260208A: Liverpool Telescope optical follow-up observations
  24. GRB 260208A: Glowbug gamma-ray detection
  25. GRB 260208A: NuSTAR detection of prompt emission
  26. GRB 260208A: Fermi GBM Observation
  27. Fermi GRB 260209A: Global MASTER-Net observations report
  28. GRB 260208B: Swift-XRT observations
  29. GRB 260131A/B: continued Mondy optical observations
  30. GRB 260204A: Swift/UVOT Upper Limits
  31. GRB 260208B: COLIBRÍ optical observations
  32. GRB 260208A: Mondy optical observations
  33. GRB 260208A: 1.3m DFOT optical detection
  34. GRB 260208A: COLIBRÍ optical observations
  35. GRB 260208B: EP-FXT observation
  36. Fermi GRB 260208C: Global MASTER-Net observations report
  37. GRB 260208B: SVOM/VT optical candidate
  38. GRB 260208A: GECAM-B observation of a bright burst
  39. GRB 260208A: Zwicky Transient Facility Follow-Up of a Fermi GRB (Trigger 792220053)
  40. GRB 260208A: SVOM/VT optical observation
  41. Fermi GRB 260208D: Global MASTER-Net observations report
  42. GRB 260208A: Swift-XRT observations
  43. GRB 260208B: SVOM/GRM observation of a bright burst
  44. GRB 260208B: Fermi GBM Detection
  45. LAT GRB 260208B: Global MASTER-Net observations report
  46. GRB 260208A : MASTER bright optical transient inside retracted Fermi error-box
  47. GRB 260208B: BALROG localization (Fermi Trigger 792237169 / GRB 260208412)
  48. Fermi GRB 260208A: Global MASTER-Net observations report
  49. GRB 260207B: Fermi GBM Detection of a Short Burst with Extended Emission
  50. GRB 260131A/B: Mondy and Terskol optical observations
  51. Fermi GRB 260207B: Global MASTER-Net observations report
  52. GRB 260206A: Swift-XRT observations
  53. Fermi trigger No 792135758: Global MASTER-Net observations report
  54. GRB 260206A (or XRB from 4U 0513-40): MAXI/GSC detection
  55. GRB 260204A: Swift-XRT observations
  56. GRB 260204A: SVOM/VT optical candidate
  57. GRB 260204A : MASTER Global robotic net optical observations
  58. Fermi GBM Sub-Threshold Detection of GRB 260204A
  59. GRB 260204A: LCO optical upper limits
  60. EP260110a: Late GTC/EMIR near-infrared observations
  61. GRB 260121A: 239Alferov CubeSat detection
  62. GRB 260131A: KAIT optical observations
  63. GRB 251230A: MeerLICHT afterglow detection
  64. GRB 260131A/B: GTC/OSIRIS+ redshift confimation
  65. GRB 260130A: Insight-HXMT/HE detection
  66. GRB 260131A/B (AT2026bwg): J-band observations by SYSU 80cm infrared telescope
  67. GRB 260131A/B (AT2026bwg): COLIBRÍ further optical observations
  68. GRB 260127A: GECAM-B observation
  69. EP260131a: Liverpool Telescope optical upper limits
  70. EP260131a: COLIBRÍ further observations
  71. EP260131a: SVOM/VT optical observation
  72. EP260131a: Xinglong optical upper limit
  73. GRB 260131A/B (AT2026bwg): COLIBRÍ optical observations and confirmation of fading
  74. GRB 260131A/B: Fermi GBM Observation
  75. EP260131a: COLIBRÍ observations of slow optical fading
  76. EP260131a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  77. EP260131a: NOT early detection of the counterpart in "rapid response mode"
  78. GRB 260131B: MAXI/GSC detection
  79. EP260131a: COLIBRÍ optical observations of the counterpart
  80. EP260131a: Las Cumbres detection of an optical counterpart
  81. GRB 260127B: AstroSat CZTI detection
  82. GRB 260130A: Fermi GBM Detection
  83. EP260131a: Einstein Probe detection of an X-ray transient
  84. GRB 260127B: Fermi GBM Detection
  85. EP260128a / GRB 260128A: COLIBRÍ optical upper limit
  86. Fermi GRB 260130A: Global MASTER-Net observations report
  87. Fermi GRB 260129A: Global MASTER-Net observations report
  88. GRB 260128B: LCO optical upper limits
  89. GRB 260128B: SVOM/COLIBRÍ (FM-GFT) optical upper limits
  90. EP260128a: J band upper limit by SYSU 80cm infrared telescope
  91. GRB 260127A: Swift-BAT refined analysis
  92. GRB 260127B: Swift-XRT observations
  93. GRB 260127A: INASAN-Kislovodsk, SAO RAS, and Terskol K-800 optical observations
  94. GRB 260128A / EP260128a: Fermi-GBM Sub-Threshold Detection
  95. EP260128a: NOT optical counterpart candidate
  96. EP260128a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  97. EP260128a: Liverpool Telescope optical observations and possible counterpart
  98. EP260128a: LCO optical upper limits
  99. EP260128a: Global MASTER-Net observations report
  100. EP260128a: Einstein Probe detection of an X-ray transient

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