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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"

5402 results found.

  1. Swift Trigger 1334535 / GRB 250718A: COLIBRÍ optical upper limits
  2. GRB 250716A: Lesedi Detection of Fading Optical Transient GOTO25eyp
  3. GRB 250717A: Fermi GBM Final Real-time Localization
  4. GRB 250716A: GOTO tentative optical counterpart candidate
  5. Fermi GRB 250716A: Global MASTER-Net observations report
  6. Fermi GRB 250715A: Global MASTER-Net observations report
  7. GRB 250702B,D,E / EP250702a: H.E.S.S. very-high-energy gamma-ray observations
  8. Fermi GRB 250714A: Global MASTER-Net observations report
  9. GRB 250706B/C: 7DT Follow-up Observations
  10. EP250711a: COLIBRÍ refined photometry and optical confirmation of the candidate
  11. EP250711a: NOT optical counterpart candidate
  12. EP candidate (ID=08500000365): COLIBRÍ optical Upper limit
  13. Fermi GRB 250711A: Global MASTER-Net observations report
  14. LIGO/Virgo/KAGRA S250711q: Identification of a GW compact binary merger candidate
  15. GRB 250702B,D,E / EP250702a: ALMA detection
  16. GRB 250702B,D,E/EP250702A: MeerKAT radio observations at 1.28GHz
  17. GRB 250702B,D,E / EP250702a: 10 GHz detection with the VLA
  18. IPN triangulation of GRB 250704B (short/hard, consistent with EP 250704a)
  19. IceCube-250706A: No Candidates from the Zwicky Transient Facility
  20. GRB 250704B / EP250704a: VLA radio detection
  21. GRB 250704B / EP250704a: Mondy and AbAO optical observations
  22. GRB 250704A: SVOM/COLIBRÍ (FM-GFT) optical observations
  23. GRB 250706B: Swift/UVOT Detection
  24. EP250702a/ GRB 250702B: NuSTAR X-ray Observations
  25. IceCube-250706A: COLIBRÍ optical upper limits
  26. GRB250706B: Swift-XRT counterpart detection
  27. GRB 250706B: iTelescope optical observations
  28. GRB 250706B: TRT bright optical counterpart detection
  29. GRB 250703A: EIRSAT-1 GMOD Detection
  30. GRB 250702F: Calapai Observatory, Massa S. Giorgio (Messina), optical observation.
  31. EP250704a / GRB 250704B: NOT observations of the optical afterglow
  32. EP250704a / GRB 250704B: VLT/X-shooter spectroscopic redshift z = 0.661
  33. GRBs 250702B,D,E / EP250702a: fast fading, extremely red counterpart
  34. GRB 250702F: GROWTH-India Telescope optical observations
  35. EP250704a: COLIBRÍ optical counterpart candidate
  36. GRB 250702F: optical photometry from Konkoly
  37. Fermi GRB 250703A: Global MASTER-Net observations report
  38. GRB 250702F: AKO Optical Afterglow Detection
  39. GRBs 250702B,C,D,E / EP250702a: VLT/HAWK-I NIR candidate
  40. GRBs 250702B,C,D,E / EP250702a: SVOM/GRM observation
  41. GRB 250702B,C,D,E/EP250702a: COLIBRÍ optical upper limit
  42. GRB 250702F: TRT Optical Observation
  43. GRB 250703A: DDOTI Optical Upper Limit
  44. EP250702a: Global MASTER-Net observations report
  45. GRB 250702F: DDOTI Optical Observation
  46. EP250702a/GRB 250702B,C,D,E: GOTO optical upper limits
  47. GRB 250702F: COLIBRÍ Observations of the Afterglow
  48. Fermi GRB 250702E: Global MASTER-Net observations report
  49. Fermi GRB 250702B: Global MASTER-Net observations report
  50. GRB 250628B: Swift-XRT observations
  51. GRB 250625A: SAO RAS possible optical afterglow
  52. GRB 250617B: Mondy and SAO RAS optical observations on 2025-06-23, 2025-06-24
  53. Fermi GRB 250623A: Global MASTER-Net observations report
  54. GRB 250617B: NUTTelA-TAO early time optical observations
  55. GRB 250617B: GOTO optical upper limit
  56. Fermi trigger No 771752663: Global MASTER-Net observations report
  57. Fermi trigger No 771718064: Global MASTER-Net observations report
  58. sb25061207: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  59. GRB 250612B (250612519/771424081): Fermi GBM Final Localization
  60. Swift GRB250612.04: Global MASTER-Net observations report
  61. EP250610a: Global MASTER-Net observations report
  62. EP250610a: Swift-XRT counterpart detection
  63. Fermi trigger No 771072240: Global MASTER-Net observations report
  64. GRB 250529A: GOTO optical counterpart candidate (GOTO25dea/AT 2025ndt)
  65. Fermi GRB 250606A: Global MASTER-Net observations report
  66. Fermi trigger No 770867684: Global MASTER-Net observations report
  67. IPN triangulation of GRB 250404B
  68. IPN triangulation of GRB 250529A
  69. Fermi Gamma-ray Burst Monitor trigger 770675211/250603852 is not a GRB
  70. GRB 250602A: DDOTI Optical Follow-Up of the Fermi/LAT Localization
  71. Fermi trigger No 770638414: Global MASTER-Net observations report
  72. Swift GRB250603.05: Global MASTER-Net observations report
  73. GRB 250602A: Fermi GBM Observation
  74. GRB 250602A: Fermi-LAT detection
  75. Fermi GRB 250601A: Global MASTER-Net observations report
  76. GRB 250602A: Fermi GBM Final Real-time Localization
  77. Fermi GRB 250531A: Global MASTER-Net observations report
  78. EP#01709177494: Swift-XRT counterpart detection of known source
  79. GRB 250521C/ZTF25aarhkyn/AT2025mgj: COLIBRÍ optical observations
  80. Swift GRB 250530C: Global MASTER-Net observations report
  81. GRB 250529A: Fermi GBM Final Real-time Localization
  82. GRB 250521C (short): Zwicky Transient Facility identification of a possible fast optical transient counterpart
  83. Fermi trigger No 770058372: Global MASTER-Net observations report
  84. EP250526a: COLIBRÍ optical upper limits
  85. EP-WXT trigger 01709176712: SVOM/C-GFT observations of blue-to-red color variation
  86. GRB 250520A: 3 GHz MeerKAT Detection
  87. Fermi GRB 250521D: Global MASTER-Net observations report
  88. Fermi trigger No 769533898: Global MASTER-Net observations report
  89. GRB 250521B: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  90. GRB 250520A: Gemini-South optical observations
  91. Swift GRB 250520A: Global MASTER-Net observations report
  92. EP-WXT trigger (ID: 01709176312): a new X-ray outburst of HMXB RX J0111.2-7317
  93. Fermi GRB 250516A: Global MASTER-Net observations report
  94. GRB 250515A:COLIBRÍ optical observations of the GOTO candidate
  95. GRB 250515A: GOTO candidate optical counterpart
  96. Konus-Wind detection of GRB 250512B / EP250512a
  97. EP250512a/GRB 250512B refined analysis of the EP-WXT and EP-FXT observations
  98. EP250511a: Mephisto optical upper limits
  99. EP250511a: Einstein Probe follow-up obsevation and refined analysis
  100. Fermi GRB 250510C: Global MASTER-Net observations report

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