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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"

5386 results found.

  1. GRB 250702B,D,E / EP250702a: 10 GHz detection with the VLA
  2. IPN triangulation of GRB 250704B (short/hard, consistent with EP 250704a)
  3. IceCube-250706A: No Candidates from the Zwicky Transient Facility
  4. GRB 250704B / EP250704a: VLA radio detection
  5. GRB 250704B / EP250704a: Mondy and AbAO optical observations
  6. GRB 250704A: SVOM/COLIBRÍ (FM-GFT) optical observations
  7. GRB 250706B: Swift/UVOT Detection
  8. EP250702a/ GRB 250702B: NuSTAR X-ray Observations
  9. IceCube-250706A: COLIBRÍ optical upper limits
  10. GRB250706B: Swift-XRT counterpart detection
  11. GRB 250706B: iTelescope optical observations
  12. GRB 250706B: TRT bright optical counterpart detection
  13. GRB 250703A: EIRSAT-1 GMOD Detection
  14. GRB 250702F: Calapai Observatory, Massa S. Giorgio (Messina), optical observation.
  15. EP250704a / GRB 250704B: NOT observations of the optical afterglow
  16. EP250704a / GRB 250704B: VLT/X-shooter spectroscopic redshift z = 0.661
  17. GRBs 250702B,D,E / EP250702a: fast fading, extremely red counterpart
  18. GRB 250702F: GROWTH-India Telescope optical observations
  19. EP250704a: COLIBRÍ optical counterpart candidate
  20. GRB 250702F: optical photometry from Konkoly
  21. Fermi GRB 250703A: Global MASTER-Net observations report
  22. GRB 250702F: AKO Optical Afterglow Detection
  23. GRBs 250702B,C,D,E / EP250702a: VLT/HAWK-I NIR candidate
  24. GRBs 250702B,C,D,E / EP250702a: SVOM/GRM observation
  25. GRB 250702B,C,D,E/EP250702a: COLIBRÍ optical upper limit
  26. GRB 250702F: TRT Optical Observation
  27. GRB 250703A: DDOTI Optical Upper Limit
  28. EP250702a: Global MASTER-Net observations report
  29. GRB 250702F: DDOTI Optical Observation
  30. EP250702a/GRB 250702B,C,D,E: GOTO optical upper limits
  31. GRB 250702F: COLIBRÍ Observations of the Afterglow
  32. Fermi GRB 250702E: Global MASTER-Net observations report
  33. Fermi GRB 250702B: Global MASTER-Net observations report
  34. GRB 250628B: Swift-XRT observations
  35. GRB 250625A: SAO RAS possible optical afterglow
  36. GRB 250617B: Mondy and SAO RAS optical observations on 2025-06-23, 2025-06-24
  37. Fermi GRB 250623A: Global MASTER-Net observations report
  38. GRB 250617B: NUTTelA-TAO early time optical observations
  39. GRB 250617B: GOTO optical upper limit
  40. Fermi trigger No 771752663: Global MASTER-Net observations report
  41. Fermi trigger No 771718064: Global MASTER-Net observations report
  42. sb25061207: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  43. GRB 250612B (250612519/771424081): Fermi GBM Final Localization
  44. Swift GRB250612.04: Global MASTER-Net observations report
  45. EP250610a: Global MASTER-Net observations report
  46. EP250610a: Swift-XRT counterpart detection
  47. Fermi trigger No 771072240: Global MASTER-Net observations report
  48. GRB 250529A: GOTO optical counterpart candidate (GOTO25dea/AT 2025ndt)
  49. Fermi GRB 250606A: Global MASTER-Net observations report
  50. Fermi trigger No 770867684: Global MASTER-Net observations report
  51. IPN triangulation of GRB 250404B
  52. IPN triangulation of GRB 250529A
  53. Fermi Gamma-ray Burst Monitor trigger 770675211/250603852 is not a GRB
  54. GRB 250602A: DDOTI Optical Follow-Up of the Fermi/LAT Localization
  55. Fermi trigger No 770638414: Global MASTER-Net observations report
  56. Swift GRB250603.05: Global MASTER-Net observations report
  57. GRB 250602A: Fermi GBM Observation
  58. GRB 250602A: Fermi-LAT detection
  59. Fermi GRB 250601A: Global MASTER-Net observations report
  60. GRB 250602A: Fermi GBM Final Real-time Localization
  61. Fermi GRB 250531A: Global MASTER-Net observations report
  62. EP#01709177494: Swift-XRT counterpart detection of known source
  63. GRB 250521C/ZTF25aarhkyn/AT2025mgj: COLIBRÍ optical observations
  64. Swift GRB 250530C: Global MASTER-Net observations report
  65. GRB 250529A: Fermi GBM Final Real-time Localization
  66. GRB 250521C (short): Zwicky Transient Facility identification of a possible fast optical transient counterpart
  67. Fermi trigger No 770058372: Global MASTER-Net observations report
  68. EP250526a: COLIBRÍ optical upper limits
  69. EP-WXT trigger 01709176712: SVOM/C-GFT observations of blue-to-red color variation
  70. GRB 250520A: 3 GHz MeerKAT Detection
  71. Fermi GRB 250521D: Global MASTER-Net observations report
  72. Fermi trigger No 769533898: Global MASTER-Net observations report
  73. GRB 250521B: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  74. GRB 250520A: Gemini-South optical observations
  75. Swift GRB 250520A: Global MASTER-Net observations report
  76. EP-WXT trigger (ID: 01709176312): a new X-ray outburst of HMXB RX J0111.2-7317
  77. Fermi GRB 250516A: Global MASTER-Net observations report
  78. GRB 250515A:COLIBRÍ optical observations of the GOTO candidate
  79. GRB 250515A: GOTO candidate optical counterpart
  80. Konus-Wind detection of GRB 250512B / EP250512a
  81. EP250512a/GRB 250512B refined analysis of the EP-WXT and EP-FXT observations
  82. EP250511a: Mephisto optical upper limits
  83. EP250511a: Einstein Probe follow-up obsevation and refined analysis
  84. Fermi GRB 250510C: Global MASTER-Net observations report
  85. Fermi GRB 250510B: Global MASTER-Net observations report
  86. GRB 250510A: Swift-XRT observations
  87. GRB 250509A: Prompt enhanced Swift-XRT position
  88. Fermi GRB 250509A: Global MASTER-Net observations report
  89. EP250508a: follow-up observation with EP-FXT
  90. EP250508a: Einstein Probe detection of an X-ray transient
  91. EP#01709175213/IGR J19566+0326: Swift-XRT detection
  92. GRB 250506A: SVOM/COLIBRÍ (FM-GFT) Upper Limits on the Optical Counterpart
  93. GRB 250504A: VLT/X-shooter upper limits
  94. GRB 250502A: Mondy and Tien-Shan Optical Observations
  95. Fermi trigger No 767975731: Global MASTER-Net observations report
  96. GRB 250430A: Kanata optical upper limit
  97. EP250427a: LT optical counterpart detection
  98. GRB 250330B: GRBAlpha detection
  99. IceCube-250421A: DDOTI Detection of the LAST Candidate
  100. EP250421A: COLIBRÍ Optical Upper Limit

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