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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"

28056 results found.

  1. GRB 260213B: BALROG localization (Fermi Trigger 792697214 / GRB 260213736)
  2. GRB 260211A: EP-FXT follow-up observation
  3. GRB 260211A: SVOM/VT optical observation
  4. GRB 260212A: Glowbug gamma-ray detection
  5. Fermi GRB 260212A: Global MASTER-Net observations report
  6. GRB 260211A: LAST optical upper limit
  7. GRB 260210A: SVOM/GRM observation
  8. Fermi GBM Sub-Threshold Detection of GRB 260211A
  9. GRID detection of GRB 260207B
  10. GRB 260211A: LCO optical upper limits
  11. GRB260131A/B: 3.6m DOT Optical Observations
  12. GRB 260211A: SVOM/COLIBRÍ (FM-GFT) optical upper limits
  13. Fermi trigger No 792537871: Global MASTER-Net observations report
  14. Swift Operations Update + Community Forum (Friday, February 13 @ 10:00 AM EST)
  15. EP260209a: COLIBRÍ optical upper limit
  16. Fermi GRB 260210C: Global MASTER-Net observations report
  17. EP260209a: LCO optical upper limits
  18. EP260210a: Global MASTER-Net observations report
  19. EP260210a: refined analysis of the EP-FXT observation
  20. EP260209a: Global MASTER-Net observations report
  21. GRB 260208A: LCO detection of the optical counterpart
  22. EP260209a: Einstein Probe detection of a fast X-ray transient
  23. EP260210a: Optical upper limits with Kinder observations
  24. GRB 260210A: Glowbug gamma-ray detection
  25. GRB 260208C: AstroSat CZTI detection
  26. EP260210a: COLIBRÍ optical upper limit
  27. EP260210a: SVOM/C-GFT upper limit
  28. EP260210a: Einstein Probe detection of an X-ray transient
  29. GRB 260207B: AstroSat CZTI detection
  30. GRB 260208C: SVOM/GRM observation
  31. GRB 260204A: Swift-XRT afterglow detection
  32. GRB 260208B: AstroSat CZTI detection of a bright long burst
  33. GRB260208A: Liverpool Telescope optical follow-up observations
  34. GRB 260208A: Glowbug gamma-ray detection
  35. GRB 260208A: NuSTAR detection of prompt emission
  36. GRB 260208A: Fermi GBM Observation
  37. Fermi GRB 260209A: Global MASTER-Net observations report
  38. GRB 260208B: Swift-XRT observations
  39. GRB 260131A/B: continued Mondy optical observations
  40. GRB 260204A: Swift/UVOT Upper Limits
  41. GRB 260208B: COLIBRÍ optical observations
  42. GRB 260208A: Mondy optical observations
  43. GRB 260208A: 1.3m DFOT optical detection
  44. GRB 260208A: COLIBRÍ optical observations
  45. GRB 260208B: EP-FXT observation
  46. Fermi GRB 260208C: Global MASTER-Net observations report
  47. GRB 260208B: SVOM/VT optical candidate
  48. GRB 260208A: GECAM-B observation of a bright burst
  49. GRB 260208A: Zwicky Transient Facility Follow-Up of a Fermi GRB (Trigger 792220053)
  50. GRB 260208A: SVOM/VT optical observation
  51. Fermi GRB 260208D: Global MASTER-Net observations report
  52. GRB 260208A: Swift-XRT observations
  53. GRB 260208B: SVOM/GRM observation of a bright burst
  54. GRB 260208B: Fermi GBM Detection
  55. LAT GRB 260208B: Global MASTER-Net observations report
  56. GRB 260208A : MASTER bright optical transient inside retracted Fermi error-box
  57. GRB 260208B: BALROG localization (Fermi Trigger 792237169 / GRB 260208412)
  58. Fermi GRB 260208A: Global MASTER-Net observations report
  59. GRB 260207B: Fermi GBM Detection of a Short Burst with Extended Emission
  60. GRB 260131A/B: Mondy and Terskol optical observations
  61. Fermi GRB 260207B: Global MASTER-Net observations report
  62. GRB 260206A: Swift-XRT observations
  63. Fermi trigger No 792135758: Global MASTER-Net observations report
  64. GRB 260206A (or XRB from 4U 0513-40): MAXI/GSC detection
  65. GRB 260204A: Swift-XRT observations
  66. GRB 260204A: SVOM/VT optical candidate
  67. GRB 260204A : MASTER Global robotic net optical observations
  68. Fermi GBM Sub-Threshold Detection of GRB 260204A
  69. GRB 260204A: LCO optical upper limits
  70. EP260110a: Late GTC/EMIR near-infrared observations
  71. GRB 260121A: 239Alferov CubeSat detection
  72. GRB 260131A: KAIT optical observations
  73. GRB 251230A: MeerLICHT afterglow detection
  74. GRB 260131A/B: GTC/OSIRIS+ redshift confimation
  75. GRB 260130A: Insight-HXMT/HE detection
  76. GRB 260131A/B (AT2026bwg): J-band observations by SYSU 80cm infrared telescope
  77. GRB 260131A/B (AT2026bwg): COLIBRÍ further optical observations
  78. GRB 260127A: GECAM-B observation
  79. EP260131a: Liverpool Telescope optical upper limits
  80. EP260131a: COLIBRÍ further observations
  81. EP260131a: SVOM/VT optical observation
  82. EP260131a: Xinglong optical upper limit
  83. GRB 260131A/B (AT2026bwg): COLIBRÍ optical observations and confirmation of fading
  84. GRB 260131A/B: Fermi GBM Observation
  85. EP260131a: COLIBRÍ observations of slow optical fading
  86. EP260131a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  87. EP260131a: NOT early detection of the counterpart in "rapid response mode"
  88. GRB 260131B: MAXI/GSC detection
  89. EP260131a: COLIBRÍ optical observations of the counterpart
  90. EP260131a: Las Cumbres detection of an optical counterpart
  91. GRB 260127B: AstroSat CZTI detection
  92. GRB 260130A: Fermi GBM Detection
  93. EP260131a: Einstein Probe detection of an X-ray transient
  94. GRB 260127B: Fermi GBM Detection
  95. EP260128a / GRB 260128A: COLIBRÍ optical upper limit
  96. Fermi GRB 260130A: Global MASTER-Net observations report
  97. Fermi GRB 260129A: Global MASTER-Net observations report
  98. GRB 260128B: LCO optical upper limits
  99. GRB 260128B: SVOM/COLIBRÍ (FM-GFT) optical upper limits
  100. EP260128a: J band upper limit by SYSU 80cm infrared telescope

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