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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"

4745 results found.

  1. sb25061207: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  2. GRB 250612B (250612519/771424081): Fermi GBM Final Localization
  3. Swift GRB250612.04: Global MASTER-Net observations report
  4. EP250610a: Global MASTER-Net observations report
  5. EP250610a: Swift-XRT counterpart detection
  6. Fermi trigger No 771072240: Global MASTER-Net observations report
  7. GRB 250529A: GOTO optical counterpart candidate (GOTO25dea/AT 2025ndt)
  8. Fermi GRB 250606A: Global MASTER-Net observations report
  9. Fermi trigger No 770867684: Global MASTER-Net observations report
  10. IPN triangulation of GRB 250404B
  11. IPN triangulation of GRB 250529A
  12. Fermi Gamma-ray Burst Monitor trigger 770675211/250603852 is not a GRB
  13. GRB 250602A: DDOTI Optical Follow-Up of the Fermi/LAT Localization
  14. Fermi trigger No 770638414: Global MASTER-Net observations report
  15. Swift GRB250603.05: Global MASTER-Net observations report
  16. GRB 250602A: Fermi GBM Observation
  17. GRB 250602A: Fermi-LAT detection
  18. Fermi GRB 250601A: Global MASTER-Net observations report
  19. GRB 250602A: Fermi GBM Final Real-time Localization
  20. Fermi GRB 250531A: Global MASTER-Net observations report
  21. EP#01709177494: Swift-XRT counterpart detection of known source
  22. GRB 250521C/ZTF25aarhkyn/AT2025mgj: COLIBRÍ optical observations
  23. Swift GRB 250530C: Global MASTER-Net observations report
  24. GRB 250529A: Fermi GBM Final Real-time Localization
  25. GRB 250521C (short): Zwicky Transient Facility identification of a possible fast optical transient counterpart
  26. Fermi trigger No 770058372: Global MASTER-Net observations report
  27. EP250526a: COLIBRÍ optical upper limits
  28. EP-WXT trigger 01709176712: SVOM/C-GFT observations of blue-to-red color variation
  29. GRB 250520A: 3 GHz MeerKAT Detection
  30. Fermi GRB 250521D: Global MASTER-Net observations report
  31. Fermi trigger No 769533898: Global MASTER-Net observations report
  32. GRB 250521B: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  33. GRB 250520A: Gemini-South optical observations
  34. Swift GRB 250520A: Global MASTER-Net observations report
  35. EP-WXT trigger (ID: 01709176312): a new X-ray outburst of HMXB RX J0111.2-7317
  36. Fermi GRB 250516A: Global MASTER-Net observations report
  37. GRB 250515A:COLIBRÍ optical observations of the GOTO candidate
  38. GRB 250515A: GOTO candidate optical counterpart
  39. Konus-Wind detection of GRB 250512B / EP250512a
  40. EP250512a/GRB 250512B refined analysis of the EP-WXT and EP-FXT observations
  41. EP250511a: Mephisto optical upper limits
  42. EP250511a: Einstein Probe follow-up obsevation and refined analysis
  43. Fermi GRB 250510C: Global MASTER-Net observations report
  44. Fermi GRB 250510B: Global MASTER-Net observations report
  45. GRB 250510A: Swift-XRT observations
  46. GRB 250509A: Prompt enhanced Swift-XRT position
  47. Fermi GRB 250509A: Global MASTER-Net observations report
  48. EP250508a: follow-up observation with EP-FXT
  49. EP250508a: Einstein Probe detection of an X-ray transient
  50. EP#01709175213/IGR J19566+0326: Swift-XRT detection
  51. GRB 250506A: SVOM/COLIBRÍ (FM-GFT) Upper Limits on the Optical Counterpart
  52. GRB 250504A: VLT/X-shooter upper limits
  53. GRB 250502A: Mondy and Tien-Shan Optical Observations
  54. Fermi trigger No 767975731: Global MASTER-Net observations report
  55. GRB 250430A: Kanata optical upper limit
  56. EP250427a: LT optical counterpart detection
  57. GRB 250330B: GRBAlpha detection
  58. IceCube-250421A: DDOTI Detection of the LAST Candidate
  59. EP250421A: COLIBRÍ Optical Upper Limit
  60. GRB 250419A: Mondy Continued Optical Observations
  61. IceCube Alert 250421.71: Global MASTER-Net observations report
  62. GRB 250419A: LCO optical afterglow multi-band observations
  63. GRB 250419A: MASTER optical afterglow observation
  64. GRB 250407A: GTC/OSIRIS+ spectroscopic redshift z = 1.36
  65. GRB 250419A: GOTO optical counterpart detection
  66. GRB 250419A: SVOM/COLIBRÍ (FM-GFT) Detection of the Optical Counterpart
  67. IceCube-250416A: DDOTI Optical Observations
  68. EP250416a: Gemini South-GMOS optical counterpart
  69. EP250225a: SVOM/VT optical brightening
  70. IceCube 250414.324: DDOTI Optical Observations
  71. EP250404a: Nanshan 0.43m Telescope optical observatios
  72. Fermi trigger No 766148493: Global MASTER-Net observations report
  73. Fermi trigger No 766173972: Global MASTER-Net observations report
  74. GRB 250407A: Continued KAIT/Nickel optical observations
  75. GRB 250320B: cubesat Avion detection
  76. IceCube-250406A: Swift-XRT observations
  77. EP250407a: Global MASTER-Net observations report
  78. GRB 250407A: COLIBRÍ/DDRAGO Detection of the Optical Counterpart
  79. IceCube-250406A: No candidates from the Zwicky Transient Facility
  80. Fermi GRB 250407A: Global MASTER-Net observations report
  81. IceCube 250406A: DDOTI Optical Observations of the Refined Position
  82. IPN triangulation of GRB 250406B (short/hard)
  83. IceCube 250406.951: COLIBRÍ/DDRAGO Optical Upper Limit
  84. IceCube 250406.951: DDOTI Optical Observations
  85. Fermi GRB 250406A: Global MASTER-Net observations report
  86. Fermi trigger No 765619921: Global MASTER-Net observations report
  87. EP250404a / GRB 250404A: J band observations by SYSU 80cm telescope
  88. GRB 250402A: Calapai Observatory, Massa S. Giorgio (Messina), optical observations.
  89. EP250402a: Optical upper limit with PD 1.3m observations
  90. GRB 250403A: AstroSat CZTI detection
  91. Fermi GRB 250404A: Global MASTER-Net observations report
  92. EP250404a: Xinglong decaying optical counterpart
  93. GRB 250403A: Montarrenti Observatory optical detection
  94. EP250404a: Global MASTER-Net observations report
  95. GRB 250403A: Fermi GBM observations
  96. GRB 250327B: VIRT Optical Upper Limit
  97. EP250404a: Mephisto multi-band optical detection
  98. GRB 250402A: Mondy optical observations
  99. GRB 250403A: Swift/UVOT Detection
  100. GRB 250402A: Swift/UVOT Upper Limits

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