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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. GRB 251221A: UAFO and Mondy optical upper limit
  2. GRB 251221A: Swift-XRT refined Analysis
  3. EP251221a: Einstein Probe detection of a fast X-ray transient
  4. GRB 251221A: Swift/UVOT Upper Limits
  5. Fermi Gamma-ray Burst Monitor trigger 788028118/251221696 is not a GRB
  6. GRB 251221A: Enhanced Swift-XRT position
  7. GRB 251221A: Fermi GBM Observation
  8. GRB 251221B: Fermi GBM Final Real-time Localization
  9. EP251220a: EP-FXT follow-up observation
  10. GRB 251220B: SVOM/GRM observation of a short burst
  11. EP251220a: COLIBRÍ confirmation of fading and photometric redshift upper limit of z < 3.4
  12. EP 251220a: GOTO optical counterpart detection
  13. GRB 251221A: COLIBRÍ detection of the optical counterpart
  14. EP 251220a: COLIBRÍ detection of the optical counterpart
  15. GRB 251221A: Swift detection of a burst
  16. Swift GRB251221A: Global MASTER-Net observations report
  17. GRB 251221A: Fermi GBM Final Real-time Localization
  18. EP251220a: Global MASTER-Net observations report
  19. EP251220a: EP detection of a fast X-ray transient
  20. SVOM GRB251220.98: Global MASTER-Net observations report
  21. GRB 251220B: Fermi GBM Final Real-time Localization
  22. GRB 251219A: SVOM/GRM observation of a short burst
  23. GRB 251219A: GECAM-B detection of a possible magnetar X-ray burst from SGR 1830-0645
  24. Fermi-LAT Gamma-ray Observations of IceCube-251218A
  25. GRB 251220A: MAXI/GSC detection
  26. GRB 251215A: Swift-XRT afterglow detection
  27. IceCube-251218A: Upper limits from a search for additional neutrino events in IceCube
  28. IceCube-251218A: COLIBRÍ optical upper limits
  29. SVOM GRB251219.11: Global MASTER-Net observations report
  30. IceCube-251218A - IceCube observation of a high-energy neutrino candidate track-like event
  31. IceCube Alert 251218.85: Global MASTER-Net observations report
  32. GRB 251214B: VIRT Optical Upper Limit
  33. Fermi trigger No 787736968: Global MASTER-Net observations report
  34. Fermi GRB 251217A: Global MASTER-Net observations report
  35. GRB 251217A: Fermi GBM Final Real-time Localization
  36. GRB 251215A: Swift/UVOT Upper LImits
  37. GRB 251215A: Fermi GBM Observation
  38. Fermi GRB 251216A: Global MASTER-Net observations report
  39. GRB 251202A/EP251202a: Koshka optical upper limit
  40. GRB 251214B: Mondy optical upper limit
  41. GRB 251215A: COLIBRÍ optical upper limit
  42. GRB 251216A: Fermi GBM Final Real-time Localization
  43. EP251214b: KAIT optical upper limit
  44. GRB 251215A: Swift-XRT observations
  45. Fermi GRB 251215A: Global MASTER-Net observations report
  46. EP251214a: Optical upper limit with Kinder observations
  47. GRB 251214B: 1.6m Mephisto observations with newly installed mosaic cameras
  48. GRB 251215A: Glowbug gamma-ray detection
  49. GRB 251214B: UAFO optical upper limit
  50. GRB 251214B: VLT/X-shooter observations
  51. GRB 251213A: GRID-10B observation
  52. GRB 251214B: Swift-BAT refined analysis
  53. GRB 251202A: radio detection with the VLA
  54. EP251214b: Global MASTER-Net observations report
  55. EP251214b : Einstein Probe detection of a fast X-ray transient
  56. EP251214b : Einstein Probe detection of a fast X-ray transient
  57. GRB 251214B: AbAO optical observations
  58. GRB 251214B: LCO detection of the optical counterpart
  59. GRB 251209A: GECAM-B observation of a long burst
  60. GRB 251214D: GECAM-B observation of a long burst
  61. GRB 251214B: Fermi GBM Observation
  62. GRB 251209A: Insight-HXMT/HE detection
  63. GRB 251215A: Swift ToO observations
  64. EP251214b (EP trigger 01709250023): LCO optical limits
  65. GRID detection of GRB 251213A
  66. GRB 251203B: AbAO optical observations
  67. GRB 251215A: Swift/BAT-GUANO arcminute localization of a burst
  68. GRB 251214B: GECAM-B observation of a long burst
  69. GRB 251214B: Swift-XRT refined Analysis
  70. GRB 251213A: SVOM/GRM observation
  71. EP251214a: KAIT optical upper limit
  72. GRB 251214D: AstroSat CZTI detection of a long burst
  73. GRB 251213A: AstroSat CZTI detection
  74. GRB 251214A: AstroSat CZTI detection
  75. GRB 251213A: GECAM-B detection
  76. GRB 251214B: Swift/UVOT Detection
  77. GRB 251215A: Fermi GBM Final Real-time Localization
  78. GRB 251214B: COLIBRÍ observations of the afterglow
  79. EP251214a: EP-FXT non-detection and upper limit
  80. GRB 251214A: GECAM-B observation of a likely long burst
  81. GRB 251214B: 1.3m DFOT optical detection
  82. EP251214a: Global MASTER-Net observations report
  83. GRB 251214B: Enhanced Swift-XRT position
  84. GRB 251214B: Xinglong-2.16m optical observation
  85. GRB 251214C: Fermi GBM Final Localization
  86. GRB 251214B : MASTER optical afterglow detection
  87. Fermi trigger No 787396657: Global MASTER-Net observations report
  88. GRB 251214B: SVOM/C-GFT optical observations
  89. EP251214a: COLIBRÍ optical upper limit
  90. Swift GRB 251214B: Global MASTER-Net observations report
  91. EP251214.305: COLIBRÍ optical upper limit
  92. GRB 251214B: Swift detection of a burst with an optical counterpart
  93. GRB 251214B: Fermi GBM Final Real-time Localization
  94. EP251214a: EP-WXT detection of an X-ray transient possibly associated with GRB 251214A
  95. Fermi GRB 251214A: Global MASTER-Net observations report
  96. GRB 251214A: Fermi GBM Final Real-time Localization
  97. EP251212a: Global MASTER-Net observations report
  98. EP251212a: KAIT optical upper limit
  99. EP251212a / GRB 251212A: AstroSat CZTI detection
  100. EP251212a: EP-FXT follow-up observation

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