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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"

21793 results found.

  1. GRB 260131A/AT2026bwg: Observations by the Zwicky Transient Facility
  2. GRB 260131A/B: GTC/OSIRIS+ redshift confimation
  3. GRB 260131A/B (AT2026bwg): J-band observations by SYSU 80cm infrared telescope
  4. GRB 260131A/B (AT2026bwg): COLIBRÍ further optical observations
  5. EP260131a: COLIBRÍ further observations
  6. GRB 260131A/B (AT2026bwg): COLIBRÍ optical observations and confirmation of fading
  7. GRB 260131A/B: GOTO candidate optical counterpart consistent with the MAXI localisation
  8. EP260131a: COLIBRÍ observations of slow optical fading
  9. EP260131a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  10. EP260131a: VLT/X-shooter spectroscopic redshift z = 0.937
  11. EP260131a: NOT early detection of the counterpart in "rapid response mode"
  12. EP260131a: COLIBRÍ optical observations of the counterpart
  13. Fermi GRB 260130A: Global MASTER-Net observations report
  14. EP260128a / GRB 260128A: NOT and TNG optical and NIR upper limits
  15. Fermi GRB 260129A: Global MASTER-Net observations report
  16. EP260128a: J band upper limit by SYSU 80cm infrared telescope
  17. GRB 260127B: Swift-XRT observations
  18. GRB 260127A: INASAN-Kislovodsk, SAO RAS, and Terskol K-800 optical observations
  19. GRB 260128A / EP260128a: Fermi-GBM Sub-Threshold Detection
  20. EP260128a: NOT optical counterpart candidate
  21. EP260128a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  22. EP260128a: Liverpool Telescope optical observations and possible counterpart
  23. EP260128a: Global MASTER-Net observations report
  24. Fermi GRB 260127A: Global MASTER-Net observations report
  25. IceCube-260125A: No Candidate Transients from the Zwicky Transient Facility
  26. GRB 260127A: COLIBRÍ optical observations
  27. GRB 260127A: NOT optical observations
  28. GRB 260127B: Swift ToO observations
  29. GRB 260127B: GOTO candidate optical counterpart
  30. GRB 260127A: SVOM/C-GFT optical observations
  31. Fermi GRB 260127B: Global MASTER-Net observations report
  32. Swift GRB 260127A: Global MASTER-Net observations report
  33. GRB 260127A: LCO optical afterglow discovery
  34. GRB 260125A: Swift-XRT observations
  35. EP260126a: EP-FXT follow-up observation
  36. EP260126a: Optical upper limit with Kinder observations
  37. EP260126a: Further NOT optical upper limits
  38. EP260126a: NOT optical observations
  39. Fermi-LAT Gamma-ray Observations of IceCube-260125A
  40. GRB 260125A: NOT optical observations on GOTO26acv / AT 2026bjf
  41. GRB 251222A: SVOM/ECLAIRs refined analysis
  42. GRB 260125A: Swift ToO observations
  43. GRB 260125A: GOTO candidate optical counterpart
  44. Fermi GRB 260125B: Global MASTER-Net observations report
  45. Swift GRB260122.97: Global MASTER-Net observations report
  46. EP260119a: Assy AZT-20 optical observations
  47. IceCube-260115A: No Candidate Transients from the Zwicky Transient Facility
  48. Fermi GRB 260120C: Global MASTER-Net observations report
  49. EP260116a: COLIBRÍ further observations
  50. GRB 251122A / EP251122a: VLT/X-shooter host redshift z = 1.765
  51. EP260105a: GTC/HiPERCAM optical observations
  52. GRB 260120B: Swift/UVOT Detection
  53. SVOM GRB260121.06: Global MASTER-Net observations report
  54. GRB 260101A: 239Alferov CubeSat detection
  55. EP260116a: COLIBRÍ observations of a tentative optical rebrightening
  56. Swift GRB260120B: Global MASTER-Net observations report
  57. EP260119A: Mondy I-Band Observations
  58. Fermi trigger No 790601190: Global MASTER-Net observations report
  59. Fermi trigger No 790570272: Global MASTER-Net observations report
  60. GRB 260114A: Swift/UVOT Upper Limits
  61. EP260119a: Liverpool Telescope optical follow-up observations
  62. GRB 251202A: further radio observations with the VLA
  63. EP260119A: GTC/OSIRIS+ spectroscopic redshift z = 5.47
  64. EP260119a: KAIT optical observations
  65. EP260119a: update of EP-FXT follow-up observation
  66. EP260119a: NOT optical observations
  67. EP260119a: SAO RAS optical observations
  68. SVOM GRB260119.92: Global MASTER-Net observations report
  69. SVOM GRB260119.92: Global MASTER-Net observations report
  70. SVOM GRB260119.90: Global MASTER-Net observations report
  71. EP260116a: COLIBRÍ detection of a fading optical source
  72. GRB 251208D: SVOM/ECLAIRs refined analysis
  73. GRB 251208D: SVOM/ECLAIRs refined analysis
  74. GRB 260117A: Swift-XRT afterglow detection
  75. EP260119a: Global MASTER-Net observations report
  76. EP260119a: LCO optical observations
  77. EP260119a: COLIBRÍ optical counterpart candidate
  78. Swift GRB260118.48: Global MASTER-Net observations report
  79. GRB 260117A: SVOM/COLIBRÍ (FM-GFT) optical observations
  80. SVOM GRB260117.82: Global MASTER-Net observations report
  81. Fermi-LAT Gamma-ray Observations of IceCube-260115A
  82. Swift trigger on the HMXB 1A 1118-61
  83. GRB 260117A: SVOM/C-GFT upper limit
  84. GRB 260117A: Swift-XRT observations
  85. GRB 260117A: Swift ToO observations
  86. Swift triggered on the HMXB 1A 1118-61
  87. FRB 20251229A: COLIBRÍ further inspection of the updated localization
  88. EP260116A: 1.3m DFOT optical upper limit
  89. GRB 260114A: VLT/MUSE spectroscopic observations
  90. EP260116a: Global MASTER-Net observations report
  91. GRB 260114A: VLT/HAWK-I further near-infrared upper limits
  92. IceCube Alert 260115.73: Global MASTER-Net observations report
  93. Fermi GRB 260115A: Global MASTER-Net observations report
  94. GRB260114A: STEP/T80S optical limits
  95. GRB 251222A: radio detection with the VLA
  96. GRB 260114A: VLT/HAWK-I near-infrared upper limits
  97. GRB 260114A: 6 GHz VLA observations
  98. GRB 260114A: VLT/X-shooter redshift of the putative host galaxy
  99. GRB 260114A: NOT optical observations
  100. Swift GRB 260114A: Global MASTER-Net observations report

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