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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. Fermi GRB 260208A: Global MASTER-Net observations report
  2. Fermi Gamma-ray Burst Monitor trigger 792220053/260208214 is not a GRB
  3. GRB 260208A: Fermi GBM Final Real-time Localization
  4. GRB 260207B: Fermi GBM Detection of a Short Burst with Extended Emission
  5. GRB 260207A : MASTER optical counterpart discovery
  6. GRB 260131A/B: Mondy and Terskol optical observations
  7. Fermi GRB 260207B: Global MASTER-Net observations report
  8. GRB 260206A: Swift-XRT observations
  9. GRB 260207B: Fermi GBM Final Real-time Localization
  10. GRB 260207A: Fermi GBM Final Localization
  11. Fermi trigger No 792135758: Global MASTER-Net observations report
  12. EP260131a: VLA detection
  13. GRB 260206A: Tiled Swift observations
  14. GRB 260206A (or XRB from 4U 0513-40): MAXI/GSC detection
  15. GRB 260204A: SVOM/VT confirms fading of the optical afterglow
  16. GRB 260204A: Swift-XRT observations
  17. GRB 260204A: LCO optical afterglow detection
  18. GRB 260204A: SVOM/VT optical candidate
  19. GRB 260204A : MASTER Global robotic net optical observations
  20. Fermi GBM Sub-Threshold Detection of GRB 260204A
  21. GRB 260204A: GOTO optical upper limit
  22. GRB 260204A: LCO optical upper limits
  23. EP260110a: Late GTC/EMIR near-infrared observations
  24. GRB 260204B: Fermi GBM Final Real-time Localization
  25. GRB 260204A: SVOM detection of a burst
  26. GRB 260121A: 239Alferov CubeSat detection
  27. Konus-Wind detection of GRB 260121A
  28. GRB 260131A/B: OHP/T193 optical observations
  29. GRB 260131A: KAIT optical observations
  30. GRB 251230A: MeerLICHT afterglow detection
  31. GRB 260131A: FTW optical and NIR observations
  32. GRB 260131A/AT2026bwg: Observations by the Zwicky Transient Facility
  33. GRID detection of GRB 260131A/B
  34. GRB 260131A/B: GTC/OSIRIS+ redshift confimation
  35. GRB 260130A: Insight-HXMT/HE detection
  36. GRB 260130A: GECAM-B observation of a short burst
  37. GRB 260131A/B (AT2026bwg): J-band observations by SYSU 80cm infrared telescope
  38. GRB 260131A/B: EP/FXT X-ray afterglow detection
  39. GRB 260131A/B (AT2026bwg): COLIBRÍ further optical observations
  40. GRB 260127B: Insight-HXMT/HE detection
  41. GRB 260127B: GECAM-B observation of a short burst
  42. GRB 260127A: GECAM-B observation
  43. GRB 260131A: NOT spectroscopic redshift z = 1.434
  44. EP260131a: Liverpool Telescope optical upper limits
  45. EP260131a: COLIBRÍ further observations
  46. Konus-Wind detection of GRB 260128A / EP260128a
  47. GRB 260131A: Insight-HXMT/HE detection
  48. Konus-Wind detection of GRB 260131A/B
  49. EP260131a: SVOM/VT optical observation
  50. EP260131a: Xinglong optical upper limit
  51. GRB 260131A/B (AT2026bwg): COLIBRÍ optical observations and confirmation of fading
  52. GRB 260131A/B: GOTO candidate optical counterpart consistent with the MAXI localisation
  53. GRB 260131A/B: Fermi GBM Observation
  54. EP260131a: COLIBRÍ observations of slow optical fading
  55. EP260131a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  56. EP260131a: VLT/X-shooter spectroscopic redshift z = 0.937
  57. EP260131a: NOT early detection of the counterpart in "rapid response mode"
  58. GRB 260131B: MAXI/GSC detection
  59. GRB 260131A: Fermi GBM Final Real-time Localization
  60. EP260131a: COLIBRÍ optical observations of the counterpart
  61. EP260131a: Las Cumbres detection of an optical counterpart
  62. GRB 260127B: AstroSat CZTI detection
  63. GRB 260130A: Fermi GBM Detection
  64. EP260131a: Einstein Probe detection of an X-ray transient
  65. GRB 260127B: Fermi GBM Detection
  66. EP260128a / GRB 260128A: COLIBRÍ optical upper limit
  67. Fermi GRB 260130A: Global MASTER-Net observations report
  68. EP260128a / GRB 260128A: NOT and TNG optical and NIR upper limits
  69. GRB 260130A: Fermi GBM Final Real-time Localization
  70. Fermi GRB 260129A: Global MASTER-Net observations report
  71. GRB 260128B: LCO optical upper limits
  72. GRB 260128B: SVOM/COLIBRÍ (FM-GFT) optical upper limits
  73. EP260128a: J band upper limit by SYSU 80cm infrared telescope
  74. IPN triangulation of GRB 260121A
  75. GRB 260127A: Swift-BAT refined analysis
  76. GRB 260129B: Fermi GBM Final Localization
  77. GRB 260128B: SVOM detection of a burst through offline search
  78. GRB 260129A: Fermi GBM Final Localization
  79. IPN triangulation of GRB 260127B (short)
  80. GRB 260127B: Swift-XRT observations
  81. GRB 260127A: INASAN-Kislovodsk, SAO RAS, and Terskol K-800 optical observations
  82. GRB 260128A / EP260128a: Fermi-GBM Sub-Threshold Detection
  83. EP260128a: NOT optical counterpart candidate
  84. EP260128a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  85. EP260128a: Liverpool Telescope optical observations and possible counterpart
  86. EP260128a: LCO optical upper limits
  87. EP260126a: SVOM/VT optical upperlimit
  88. EP260128a: Global MASTER-Net observations report
  89. EP260128a: Einstein Probe detection of an X-ray transient
  90. Fermi GRB 260127A: Global MASTER-Net observations report
  91. IceCube-260125A: No Candidate Transients from the Zwicky Transient Facility
  92. GRB 260127A: Fermi GBM Observation
  93. IceCube-260125A: Upper limits from a search for additional neutrino events in IceCube
  94. GRB 260127A: COLIBRÍ optical observations
  95. GRB 260127A: NOT optical observations
  96. GRB 260127B: Swift ToO observations
  97. EP260126a: Seimei/TriCCS optical upper limit
  98. GRB 260127A : MITSuME Akeno optical afterglow candidate detection
  99. GRB 260127A: Swift-XRT refined Analysis
  100. GRB 260127B: GOTO candidate optical counterpart

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