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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. LAT GRB 260208B: Global MASTER-Net observations report
  2. GRB 260208B: Fermi-LAT detection
  3. GRB 260208C: Fermi GBM Final Real-time Localization
  4. GRB 260208A: Fermi-LAT detection
  5. GRB 260207B: GECAM-B observation
  6. GRB 260208A: Swift ToO observations
  7. GRB 260208A: Fermi GBM Classification Correction
  8. GRB 260208A: GOTO detection of a potential optical counterpart (GOTO26aob)
  9. GRB 260208A : MASTER bright optical transient inside retracted Fermi error-box
  10. GRB 260208B: BALROG localization (Fermi Trigger 792237169 / GRB 260208412)
  11. GRB 260208B: Fermi GBM Final Real-time Localization
  12. Fermi GRB 260208A: Global MASTER-Net observations report
  13. Fermi Gamma-ray Burst Monitor trigger 792220053/260208214 is not a GRB
  14. GRB 260208A: Fermi GBM Final Real-time Localization
  15. GRB 260207B: Fermi GBM Detection of a Short Burst with Extended Emission
  16. GRB 260207A : MASTER optical counterpart discovery
  17. GRB 260131A/B: Mondy and Terskol optical observations
  18. Fermi GRB 260207B: Global MASTER-Net observations report
  19. GRB 260206A: Swift-XRT observations
  20. GRB 260207B: Fermi GBM Final Real-time Localization
  21. GRB 260207A: Fermi GBM Final Localization
  22. Fermi trigger No 792135758: Global MASTER-Net observations report
  23. EP260131a: VLA detection
  24. GRB 260206A: Tiled Swift observations
  25. GRB 260206A (or XRB from 4U 0513-40): MAXI/GSC detection
  26. GRB 260204A: SVOM/VT confirms fading of the optical afterglow
  27. GRB 260204A: Swift-XRT observations
  28. GRB 260204A: LCO optical afterglow detection
  29. GRB 260204A: SVOM/VT optical candidate
  30. GRB 260204A : MASTER Global robotic net optical observations
  31. Fermi GBM Sub-Threshold Detection of GRB 260204A
  32. GRB 260204A: GOTO optical upper limit
  33. GRB 260204A: LCO optical upper limits
  34. EP260110a: Late GTC/EMIR near-infrared observations
  35. GRB 260204B: Fermi GBM Final Real-time Localization
  36. GRB 260204A: SVOM detection of a burst
  37. GRB 260121A: 239Alferov CubeSat detection
  38. Konus-Wind detection of GRB 260121A
  39. GRB 260131A/B: OHP/T193 optical observations
  40. GRB 260131A: KAIT optical observations
  41. GRB 251230A: MeerLICHT afterglow detection
  42. GRB 260131A: FTW optical and NIR observations
  43. GRB 260131A/AT2026bwg: Observations by the Zwicky Transient Facility
  44. GRID detection of GRB 260131A/B
  45. GRB 260131A/B: GTC/OSIRIS+ redshift confimation
  46. GRB 260130A: Insight-HXMT/HE detection
  47. GRB 260130A: GECAM-B observation of a short burst
  48. GRB 260131A/B (AT2026bwg): J-band observations by SYSU 80cm infrared telescope
  49. GRB 260131A/B: EP/FXT X-ray afterglow detection
  50. GRB 260131A/B (AT2026bwg): COLIBRÍ further optical observations
  51. GRB 260127B: Insight-HXMT/HE detection
  52. GRB 260127B: GECAM-B observation of a short burst
  53. GRB 260127A: GECAM-B observation
  54. GRB 260131A: NOT spectroscopic redshift z = 1.434
  55. EP260131a: Liverpool Telescope optical upper limits
  56. EP260131a: COLIBRÍ further observations
  57. Konus-Wind detection of GRB 260128A / EP260128a
  58. GRB 260131A: Insight-HXMT/HE detection
  59. Konus-Wind detection of GRB 260131A/B
  60. EP260131a: SVOM/VT optical observation
  61. EP260131a: Xinglong optical upper limit
  62. GRB 260131A/B (AT2026bwg): COLIBRÍ optical observations and confirmation of fading
  63. GRB 260131A/B: GOTO candidate optical counterpart consistent with the MAXI localisation
  64. GRB 260131A/B: Fermi GBM Observation
  65. EP260131a: COLIBRÍ observations of slow optical fading
  66. EP260131a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  67. EP260131a: VLT/X-shooter spectroscopic redshift z = 0.937
  68. EP260131a: NOT early detection of the counterpart in "rapid response mode"
  69. GRB 260131B: MAXI/GSC detection
  70. GRB 260131A: Fermi GBM Final Real-time Localization
  71. EP260131a: COLIBRÍ optical observations of the counterpart
  72. EP260131a: Las Cumbres detection of an optical counterpart
  73. GRB 260127B: AstroSat CZTI detection
  74. GRB 260130A: Fermi GBM Detection
  75. EP260131a: Einstein Probe detection of an X-ray transient
  76. GRB 260127B: Fermi GBM Detection
  77. EP260128a / GRB 260128A: COLIBRÍ optical upper limit
  78. Fermi GRB 260130A: Global MASTER-Net observations report
  79. EP260128a / GRB 260128A: NOT and TNG optical and NIR upper limits
  80. GRB 260130A: Fermi GBM Final Real-time Localization
  81. Fermi GRB 260129A: Global MASTER-Net observations report
  82. GRB 260128B: LCO optical upper limits
  83. GRB 260128B: SVOM/COLIBRÍ (FM-GFT) optical upper limits
  84. EP260128a: J band upper limit by SYSU 80cm infrared telescope
  85. IPN triangulation of GRB 260121A
  86. GRB 260127A: Swift-BAT refined analysis
  87. GRB 260129B: Fermi GBM Final Localization
  88. GRB 260128B: SVOM detection of a burst through offline search
  89. GRB 260129A: Fermi GBM Final Localization
  90. IPN triangulation of GRB 260127B (short)
  91. GRB 260127B: Swift-XRT observations
  92. GRB 260127A: INASAN-Kislovodsk, SAO RAS, and Terskol K-800 optical observations
  93. GRB 260128A / EP260128a: Fermi-GBM Sub-Threshold Detection
  94. EP260128a: NOT optical counterpart candidate
  95. EP260128a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  96. EP260128a: Liverpool Telescope optical observations and possible counterpart
  97. EP260128a: LCO optical upper limits
  98. EP260126a: SVOM/VT optical upperlimit
  99. EP260128a: Global MASTER-Net observations report
  100. EP260128a: Einstein Probe detection of an X-ray transient

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