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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').
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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"

20960 results found.

  1. EP260119a: Assy AZT-20 optical observations
  2. IceCube-260115A: No Candidate Transients from the Zwicky Transient Facility
  3. Fermi GRB 260120C: Global MASTER-Net observations report
  4. EP260116a: COLIBRÍ further observations
  5. EP260105a: GTC/HiPERCAM optical observations
  6. GRB 260120B: Swift/UVOT Detection
  7. SVOM GRB260121.06: Global MASTER-Net observations report
  8. GRB 260101A: 239Alferov CubeSat detection
  9. EP260116a: COLIBRÍ observations of a tentative optical rebrightening
  10. Swift GRB260120B: Global MASTER-Net observations report
  11. EP260119A: Mondy I-Band Observations
  12. Fermi trigger No 790601190: Global MASTER-Net observations report
  13. Fermi trigger No 790570272: Global MASTER-Net observations report
  14. GRB 260114A: Swift/UVOT Upper Limits
  15. EP260119a: Liverpool Telescope optical follow-up observations
  16. GRB 251202A: further radio observations with the VLA
  17. EP260119A: GTC/OSIRIS+ spectroscopic redshift z = 5.47
  18. EP260119a: KAIT optical observations
  19. EP260119a: update of EP-FXT follow-up observation
  20. EP260119a: NOT optical observations
  21. EP260119a: SAO RAS optical observations
  22. SVOM GRB260119.92: Global MASTER-Net observations report
  23. SVOM GRB260119.92: Global MASTER-Net observations report
  24. SVOM GRB260119.90: Global MASTER-Net observations report
  25. EP260116a: COLIBRÍ detection of a fading optical source
  26. GRB 251208D: SVOM/ECLAIRs refined analysis
  27. GRB 251208D: SVOM/ECLAIRs refined analysis
  28. GRB 260117A: Swift-XRT afterglow detection
  29. EP260119a: Global MASTER-Net observations report
  30. EP260119a: LCO optical observations
  31. EP260119a: COLIBRÍ optical counterpart candidate
  32. Swift GRB260118.48: Global MASTER-Net observations report
  33. GRB 260117A: SVOM/COLIBRÍ (FM-GFT) optical observations
  34. SVOM GRB260117.82: Global MASTER-Net observations report
  35. Fermi-LAT Gamma-ray Observations of IceCube-260115A
  36. Swift trigger on the HMXB 1A 1118-61
  37. GRB 260117A: SVOM/C-GFT upper limit
  38. GRB 260117A: Swift-XRT observations
  39. GRB 260117A: Swift ToO observations
  40. Swift triggered on the HMXB 1A 1118-61
  41. FRB 20251229A: COLIBRÍ further inspection of the updated localization
  42. EP260116A: 1.3m DFOT optical upper limit
  43. GRB 260114A: VLT/MUSE spectroscopic observations
  44. EP260116a: Global MASTER-Net observations report
  45. GRB 260114A: VLT/HAWK-I further near-infrared upper limits
  46. IceCube Alert 260115.73: Global MASTER-Net observations report
  47. Fermi GRB 260115A: Global MASTER-Net observations report
  48. GRB260114A: STEP/T80S optical limits
  49. GRB 251222A: radio detection with the VLA
  50. GRB 260114A: VLT/HAWK-I near-infrared upper limits
  51. GRB 260114A: 6 GHz VLA observations
  52. GRB 260114A: VLT/X-shooter redshift of the putative host galaxy
  53. GRB 260114A: NOT optical observations
  54. Swift GRB 260114A: Global MASTER-Net observations report
  55. GRB 260114A: Mondy optical observations
  56. Fermi-LAT Gamma-ray Observations of IceCube-260111A
  57. EP-WXT trigger 01709251266: SVOM/C-GFT confirmation of a stellar flare
  58. Swift GRB260113.43: Global MASTER-Net observations report
  59. EP260110a: NOT and GTC Optical and Near-Infrared Observations
  60. EP260110a: TRT optical upper limits
  61. GRB 260111A: Swift-XRT observations
  62. GRB 260111A: GOTO optical upper limits
  63. GRB 260111A: Swift ToO observations
  64. GRB 251230A: Mondy Optical Observations
  65. GRB 260111A: Swift/BAT-GUANO arcminute localization of a burst
  66. IceCube Alert 260111A: Global MASTER-Net observations report
  67. EP260110a: Global MASTER-Net observations report
  68. Fermi GRB 260111A: Global MASTER-Net observations report
  69. EP260110a: refined analysis of the EP-WXT and EP-FXT observations
  70. EP 260110a: COLIBRÍ optical observations
  71. EP260110a: SVOM/C-GFT upper limit
  72. GRB 260109C: LCO optical upper limits
  73. GRB 260109C: Kilonova-Catcher optical upper limit
  74. GRB 260102A: Swift-XRT afterglow detection
  75. Fermi GRB 260107A: Global MASTER-Net observations report
  76. GRB 260102A: AbAO optical observations
  77. EP260105b/EP-WXT trigger 01709251028: Einstein Probe detection of an X-ray transient
  78. Fermi GRB 260105A: Global MASTER-Net observations report
  79. EP260105a: FTW optical observations
  80. EP260104a: FTW optical observations
  81. Fermi GRB 260105B: Global MASTER-Net observations report
  82. EP260105a: refined analysis of the EP-WXT and EP-FXT observations
  83. EP260105a: LCO Optical Upper limit
  84. EP260104a: Global MASTER-Net observations report
  85. EP260104a: Einstein Probe detection of a fast X-ray transient
  86. EP260105a: Global MASTER-Net observations report
  87. Fermi GRB 260104B: Global MASTER-Net observations report
  88. Swift GRB 260104A: Global MASTER-Net observations report
  89. GRB 251230A/EP-WXT trigger 01709250693: Mephisto optical upper limits
  90. GRB 260101A: Swift/UVOT Detection
  91. Fermi-LAT Gamma-ray Observations of IceCube-251225A
  92. GRB 260101A: COLIBRÍ optical observations
  93. SVOM GRB260103.08: Global MASTER-Net observations report
  94. SVOM GRB260102A: Global MASTER-Net observations report
  95. EP260101a: Global MASTER-Net observations report
  96. GRB 260102A: Swift-XRT observations
  97. GRB 260102A: SVOM/COLIBRÍ (FM-GFT) optical observations
  98. GRB 260102A: Swift ToO observations
  99. EP260101a: refined analysis of the EP-WXT and EP-FXT observations
  100. GRB 260101A: NOT spectroscopic observations

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