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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"

21319 results found.

  1. GRB 260208A: Swift-XRT observations
  2. GRB 260208B: Swift ToO observations
  3. LAT GRB 260208B: Global MASTER-Net observations report
  4. GRB 260208A: Swift ToO observations
  5. GRB 260208A: GOTO detection of a potential optical counterpart (GOTO26aob)
  6. GRB 260208A : MASTER bright optical transient inside retracted Fermi error-box
  7. Fermi GRB 260208A: Global MASTER-Net observations report
  8. GRB 260207A : MASTER optical counterpart discovery
  9. GRB 260131A/B: Mondy and Terskol optical observations
  10. Fermi GRB 260207B: Global MASTER-Net observations report
  11. GRB 260206A: Swift-XRT observations
  12. Fermi trigger No 792135758: Global MASTER-Net observations report
  13. EP260131a: VLA detection
  14. GRB 260206A: Tiled Swift observations
  15. GRB 260204A: Swift-XRT observations
  16. GRB 260204A: LCO optical afterglow detection
  17. GRB 260204A : MASTER Global robotic net optical observations
  18. Fermi GBM Sub-Threshold Detection of GRB 260204A
  19. GRB 260204A: GOTO optical upper limit
  20. EP260110a: Late GTC/EMIR near-infrared observations
  21. GRB 260204A: SVOM detection of a burst
  22. GRB 260121A: 239Alferov CubeSat detection
  23. GRB 260131A/B: OHP/T193 optical observations
  24. GRB 260131A: KAIT optical observations
  25. GRB 251230A: MeerLICHT afterglow detection
  26. GRB 260131A: FTW optical and NIR observations
  27. GRB 260131A/AT2026bwg: Observations by the Zwicky Transient Facility
  28. GRB 260131A/B: GTC/OSIRIS+ redshift confimation
  29. GRB 260131A/B (AT2026bwg): J-band observations by SYSU 80cm infrared telescope
  30. GRB 260131A/B (AT2026bwg): COLIBRÍ further optical observations
  31. EP260131a: COLIBRÍ further observations
  32. GRB 260131A/B (AT2026bwg): COLIBRÍ optical observations and confirmation of fading
  33. GRB 260131A/B: GOTO candidate optical counterpart consistent with the MAXI localisation
  34. EP260131a: COLIBRÍ observations of slow optical fading
  35. EP260131a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  36. EP260131a: VLT/X-shooter spectroscopic redshift z = 0.937
  37. EP260131a: NOT early detection of the counterpart in "rapid response mode"
  38. EP260131a: COLIBRÍ optical observations of the counterpart
  39. Fermi GRB 260130A: Global MASTER-Net observations report
  40. EP260128a / GRB 260128A: NOT and TNG optical and NIR upper limits
  41. Fermi GRB 260129A: Global MASTER-Net observations report
  42. EP260128a: J band upper limit by SYSU 80cm infrared telescope
  43. GRB 260127B: Swift-XRT observations
  44. GRB 260127A: INASAN-Kislovodsk, SAO RAS, and Terskol K-800 optical observations
  45. GRB 260128A / EP260128a: Fermi-GBM Sub-Threshold Detection
  46. EP260128a: NOT optical counterpart candidate
  47. EP260128a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  48. EP260128a: Liverpool Telescope optical observations and possible counterpart
  49. EP260128a: Global MASTER-Net observations report
  50. Fermi GRB 260127A: Global MASTER-Net observations report
  51. IceCube-260125A: No Candidate Transients from the Zwicky Transient Facility
  52. GRB 260127A: COLIBRÍ optical observations
  53. GRB 260127A: NOT optical observations
  54. GRB 260127B: Swift ToO observations
  55. GRB 260127B: GOTO candidate optical counterpart
  56. GRB 260127A: SVOM/C-GFT optical observations
  57. Fermi GRB 260127B: Global MASTER-Net observations report
  58. Swift GRB 260127A: Global MASTER-Net observations report
  59. GRB 260127A: LCO optical afterglow discovery
  60. GRB 260125A: Swift-XRT observations
  61. EP260126a: EP-FXT follow-up observation
  62. EP260126a: Optical upper limit with Kinder observations
  63. EP260126a: Further NOT optical upper limits
  64. EP260126a: NOT optical observations
  65. Fermi-LAT Gamma-ray Observations of IceCube-260125A
  66. GRB 260125A: NOT optical observations on GOTO26acv / AT 2026bjf
  67. GRB 251222A: SVOM/ECLAIRs refined analysis
  68. GRB 260125A: Swift ToO observations
  69. GRB 260125A: GOTO candidate optical counterpart
  70. Fermi GRB 260125B: Global MASTER-Net observations report
  71. Swift GRB260122.97: Global MASTER-Net observations report
  72. EP260119a: Assy AZT-20 optical observations
  73. IceCube-260115A: No Candidate Transients from the Zwicky Transient Facility
  74. Fermi GRB 260120C: Global MASTER-Net observations report
  75. EP260116a: COLIBRÍ further observations
  76. GRB 251122A / EP251122a: VLT/X-shooter host redshift z = 1.765
  77. EP260105a: GTC/HiPERCAM optical observations
  78. GRB 260120B: Swift/UVOT Detection
  79. SVOM GRB260121.06: Global MASTER-Net observations report
  80. GRB 260101A: 239Alferov CubeSat detection
  81. EP260116a: COLIBRÍ observations of a tentative optical rebrightening
  82. Swift GRB260120B: Global MASTER-Net observations report
  83. EP260119A: Mondy I-Band Observations
  84. Fermi trigger No 790601190: Global MASTER-Net observations report
  85. Fermi trigger No 790570272: Global MASTER-Net observations report
  86. GRB 260114A: Swift/UVOT Upper Limits
  87. EP260119a: Liverpool Telescope optical follow-up observations
  88. GRB 251202A: further radio observations with the VLA
  89. EP260119A: GTC/OSIRIS+ spectroscopic redshift z = 5.47
  90. EP260119a: KAIT optical observations
  91. EP260119a: update of EP-FXT follow-up observation
  92. EP260119a: NOT optical observations
  93. EP260119a: SAO RAS optical observations
  94. SVOM GRB260119.92: Global MASTER-Net observations report
  95. SVOM GRB260119.92: Global MASTER-Net observations report
  96. SVOM GRB260119.90: Global MASTER-Net observations report
  97. EP260116a: COLIBRÍ detection of a fading optical source
  98. GRB 251208D: SVOM/ECLAIRs refined analysis
  99. GRB 251208D: SVOM/ECLAIRs refined analysis
  100. GRB 260117A: Swift-XRT afterglow detection

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