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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"

20562 results found.

  1. EP250610a: Upper limit from Fermi-GBM Observations
  2. GRB 250610B: Liverpool Telescope continued monitoring
  3. GRB 250610B: MISTRAL/T193 and T120 OHP further observations
  4. EP250610a: continuous follow-up observations with EP-FXT
  5. GRB 250610B - SVOM/ECLAIRs refined analysis
  6. Swift GRB250612.04: Global MASTER-Net observations report
  7. Fermi GBM Sub-Threshold Detection of GRB 250610B
  8. GRB 250610B: Swift/UVOT Detection
  9. EP250610A: Swift/UVOT Upper limits
  10. GRB 250610B: SVOM/COLIBRÍ (FM-GFT) optical observations
  11. GRB 250610B: REM optical/NIR observations
  12. GRB 250610B: SVOM/VT optical shallow decay
  13. GRB 250610B: additional Liverpool Telescope optical observations
  14. GRB 250610B: Swift-XRT counterpart detection
  15. GRB 250610B: LT detection of the optical counterpart
  16. GRB 250610B: GOTO optical upper limit
  17. EP250610a: Global MASTER-Net observations report
  18. GRB 250610B : SVOM/GWAC-F60A and F50 observations
  19. EP250610a: refined analysis of the EP-WXT and EP-FXT observations
  20. EP250610a: REM optical/NIR observations
  21. EP250610a: Swift-XRT counterpart detection
  22. EP250610a: COLIBRÍ optical upper limit
  23. Fermi trigger No 771072240: Global MASTER-Net observations report
  24. GRB 250609A: Swift/BAT-GUANO localization skymap of a likely short burst
  25. GRB 250605A: Swift/UVOT Upper Limits
  26. GRB 250529A: GOTO optical counterpart candidate (GOTO25dea/AT 2025ndt)
  27. GRB 250527C: CrAO Optical Upper Limit
  28. EP-WXT trigger 01709178244: confirmation of a stellar flare by BOOTES-5 & BOOTES-7
  29. EP-WXT trigger 01709178069: confirmation of a stellar flare by BOOTES-6 & BOOTES-7
  30. GRB 250605A: SVOM/VT optical upper limit
  31. EP/WXT 01709177873: GOTO observations confirm stellar variability
  32. Fermi GRB 250606A: Global MASTER-Net observations report
  33. Fermi trigger No 770867684: Global MASTER-Net observations report
  34. GRB 250605A: LT optical observations
  35. Swift GRB250605.79: Global MASTER-Net observations report
  36. GRB 250601A: PRIME H band upper limit.
  37. GRB 250530A: SVOM/GRM analysis
  38. GRB 250601A: PRIME J band upper limit.
  39. GRB 250601A: VLT/FORS2 Optical Observation
  40. GRB 250602A: DDOTI Optical Follow-Up of the Fermi/LAT Localization
  41. GRB 250603A: Swift/UVOT Upper Limits
  42. Fermi trigger No 770638414: Global MASTER-Net observations report
  43. Swift GRB250603.05: Global MASTER-Net observations report
  44. GRB 250602A: DDOTI Optical Upper Limit
  45. GRB 250521C: NOT spectroscopic observations exclude the afterglow candidate AT2025mgj
  46. GRB 250601A: Swift/XRT candidate afterglow
  47. GRB 250521C / AT2025mgj: Pan-STARRS multi-band and multi-epoch imaging and photometry
  48. GRB 250601A: Swift-XRT observations
  49. Fermi GRB 250601A: Global MASTER-Net observations report
  50. Fermi trigger No 770470765: Global MASTER-Net observations report
  51. GRB 250601A: Swift/BAT-GUANO arcminute localization of a likely short burst
  52. GRB 250601A: Swift ToO observations
  53. GRB 250521C/AT2025mgj: FTW optical and NIR observations
  54. EP#01709177494: SVOM/VT optical observations
  55. Fermi GRB 250531A: Global MASTER-Net observations report
  56. EP#01709177494: Swift-XRT counterpart detection of known source
  57. GRB 250521C/ZTF25aarhkyn/AT2025mgj: COLIBRÍ optical observations
  58. Swift GRB 250530C: Global MASTER-Net observations report
  59. GRB 250521C/AT2025mgj: NOT optical observations of the afterglow candidate
  60. GRB 250530A: SVOM/VT optical upper limit
  61. GRB 250530A: Swift-XRT counterpart detection
  62. GRB 250530A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate
  63. GRB 250527C: Swift/UVOT Upper Limits
  64. GRB 250527D: Swift/BAT-GUANO localization skymap of a burst
  65. GRB 250527B: Swift-XRT observations
  66. GRB 250521C (short): Zwicky Transient Facility identification of a possible fast optical transient counterpart
  67. GRB 250527C: Swift ToO observations
  68. GRB 250527C: Swift/BAT-GUANO arcminute localization of a burst
  69. EP250526a: SVOM/VT optical upper limit
  70. GRB 250521D: SVOM/GRM analysis suggests a possible “long” duration type I burst
  71. GRB 250527B: Tiled Swift observations
  72. GRB 250520A: Gemini-South optical afterglow detection
  73. Fermi trigger No 770058372: Global MASTER-Net observations report
  74. Fermi trigger No 770047117: Global MASTER-Net observations report
  75. EP250526a: refined analysis of the EP-WXT and EP-FXT observations
  76. GRB 250314A: CIDER NB1008 upper limit
  77. EP250526a: Global MASTER-Net observations report
  78. EP-WXT trigger 01709176712: SVOM/C-GFT observations of blue-to-red color variation
  79. GRB 250520A: 3 GHz MeerKAT Detection
  80. GRB 250520A: 10 GHz VLA Afterglow Confirmation
  81. Fermi GRB 250523A: Global MASTER-Net observations report
  82. Fermi trigger No 769611916: Global MASTER-Net observations report
  83. EP-WXT trigger 01709176712: GOTO observations confirm stellar counterpart variability
  84. GRB 250521B: SVOM/VT optical upper limit
  85. The EP-WXT trigger 01709176612: SVOM/VT optical observations
  86. The EP-WXT trigger 01709176612: refined analysis of the EP-FXT observation
  87. Fermi GRB 250522B: Global MASTER-Net observations report
  88. GRB 250521D: SVOM/VT optical observations
  89. EP#01709176612: Swift-XRT counterpart detection of flaring star
  90. Fermi GRB 250521D: Global MASTER-Net observations report
  91. Fermi trigger No 769533898: Global MASTER-Net observations report
  92. Fermi trigger No 769499303: Global MASTER-Net observations report
  93. GRB 250521D: DDOTI Optical Upper Limit
  94. GRB 250521D: GOTO detects LAST counterpart candidate prior to the GRB
  95. GRB 250521B: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  96. GRB 250521D: LAST tentative optical counterpart candidate
  97. GRB 250520A: 10 GHz VLA radio source
  98. GRB 250521B: Swift ToO observations
  99. GRB 250521A: DDOTI Optical Upper Limit
  100. GRB 250520A: VLT/FORS2 Optical Observation

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