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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"

4879 results found.

  1. EP-WXT trigger 01709176712: GOTO observations confirm stellar counterpart variability
  2. Fermi GRB 250522B: Global MASTER-Net observations report
  3. GRB 250522A: Fermi GBM Final Real-time Localization
  4. GRB 250521D: GOTO detects LAST counterpart candidate prior to the GRB
  5. GRB 250520A: Swift-XRT refined Analysis
  6. Fermi GRB 250516A: Global MASTER-Net observations report
  7. GRB 250516A: Swift-XRT refined Analysis
  8. Fermi GRB 250512A: Global MASTER-Net observations report
  9. EP250512a: Global MASTER-Net observations report
  10. Fermi GRB 250510C: Global MASTER-Net observations report
  11. GRB 250510C: Fermi GBM Final Real-time Localization
  12. IceCube-250506A: No Transient Candidates from the Zwicky Transient Facility
  13. GRB 250509A: Swift-XRT refined Analysis
  14. EP250508a: Liverpool Telescope optical upper limits
  15. GRB 250502A: Calapai Observatory, Massa S. Giorgio (Messina), optical observation.
  16. EP250508a: Global MASTER-Net observations report
  17. GRB 250504A: Swift-XRT refined Analysis
  18. Fermi GRB 250502B: Global MASTER-Net observations report
  19. GRB 250430A: SVOM/VT optical observations
  20. GRB 250424A: CALET Gamma-Ray Burst Monitor detection
  21. Fermi trigger No 767623859: Global MASTER-Net observations report
  22. EP250428b: SAO RAS optical upper limit
  23. GRB 250424A: LCO optical observation
  24. EP250427a: TRT optical counterpart detection
  25. GRB 250424A: WINTER J-band detection
  26. GRB 250424A: EIRSAT-1 GMOD Detection
  27. GRB 250424A: SVOM/VT optical observation
  28. GRB 250424A: Swift-XRT refined Analysis
  29. GRB 250424A: AstroSat CZTI detection of a bright long burst
  30. GRB 250424A: BlackGEM optical afterglow detection
  31. GRB 250424A: DDOTI Afterglow Detection
  32. GRB 250424A: REM optical/NIR afterglow detection
  33. Swift GRB 250424A: Global MASTER-Net observations report
  34. Swift GRB 250424A: Global MASTER-Net OT detection
  35. SVOM/sb25042207: BOOTES-2 early optical upper limit
  36. EP250421a: Swift/XRT counterpart detection
  37. Fermi GRB 250421A: Global MASTER-Net observations report
  38. IceCube Alert 250421.71: Global MASTER-Net observations report
  39. EP250421a: JinShan likely optical counterpart
  40. The EP-WXT trigger 01709135179: Kinder optical counterpart candidate
  41. GRB 250419A: VLT/X-shooter spectroscopic redshift z = 0.845
  42. IceCube-250416A: DDOTI Optical Observations
  43. EP250404a: Nanshan 0.43m Telescope optical observatios
  44. Fermi trigger No 766148493: Global MASTER-Net observations report
  45. Fermi trigger No 766173972: Global MASTER-Net observations report
  46. Fermi GRB 250411A: Global MASTER-Net observations report
  47. IPN triangulation of GRB 250407A
  48. Fermi GRB 250407A: Global MASTER-Net observations report
  49. IceCube 250406.951: DDOTI Optical Observations
  50. IceCube Alert 250406.95: Global MASTER-Net observations report
  51. EP250404a / GRB 250404A: Montarrenti Observatory optical observations
  52. GRB 250404A / EP250404a: SVOM/GWAC-F60 and F50 observations
  53. GRB 250404A / EP250404a: GMG spectroscopic redshift at z ~ 2.627
  54. GRB 250404A / EP250404a: Leavitt Observatory optical counterpart detection
  55. Fermi GRB 250404A: Global MASTER-Net observations report
  56. EP250404a: Xinglong decaying optical counterpart
  57. GRB 250403A: Montarrenti Observatory optical detection
  58. EP250404a: Global MASTER-Net observations report
  59. EP250404a: Nanshan/HMT optical counterpart detection
  60. GRB 250403A: Swift/UVOT Detection
  61. EP250402a: Optical upper limit with Kinder observations
  62. GRB 250403A: Swift-XRT observations
  63. GRB 250403A: GOTO optical counterpart follow-up observations
  64. GRB 250403A: GMG Optical Observation
  65. GRB 250331C: Swift-XRT refined Analysis
  66. GRB 250331B: Swift-XRT refined Analysis
  67. GRB 250331B: Swift-XRT refined Analysis
  68. Fermi GRB 250331E: Global MASTER-Net observations report
  69. LIGO/Virgo/KAGRA S250328ae: Swift XRT observations, 34 possible X-ray sources
  70. GRB 250331B: Swift detection of a burst
  71. GRB 250331A: MAXI/GSC detection
  72. GRB 250330A: Swift-XRT afterglow detection
  73. IceCube Alert 250330.35: Global MASTER-Net observations report
  74. GRB 250327B: CrAO and SAO RAS Optical Observations
  75. GRB 250327B: Swift-XRT detection of the X-ray afterglow
  76. GRB 250327A: Swift-XRT refined Analysis
  77. GRB 250327B: GOTO optical counterpart detection
  78. FRB 20250316A: Gemini Imaging and Spectroscopy of the Sub-arcsecond Localization Region of FRB 20250316A
  79. EP250324A: COLIBRÍ/DDRAGO Optical Observations
  80. GRB 250322A: Swift-XRT refined Analysis
  81. GRB 250322A: AstroSat CZTI detection of a short burst
  82. FRB 250316A: DDOTI Continued Optical Observations
  83. EP250321a: Liverpool Telescope optical follow-up
  84. GRB 250312A: GECAM-A detection
  85. GRB 250321A: Swift-BAT refined analysis
  86. GRB 250321A: Swift-XRT refined Analysis
  87. GRB 250317B: NOT optical observations suggest an optical plateau phase
  88. Fermi GRB 250316A: Global MASTER-Net observations report
  89. GRB 250313.89 / Fermi trigger 763594063: bright OT AT 2025ehi detection
  90. Fermi GRB 250313A: Global MASTER-Net observations report
  91. GRB 250312A: Swift-XRT refined Analysis
  92. GRB 250312A: Swift detection of a burst
  93. GRB 250309B: 1.3m DFOT Optical observations
  94. IPN triangulation of GRB 250308A (short)
  95. IceCube-241224A: MASTER detection of PKS 1217+02 blazar flare with Zhirkov effect
  96. GRB 250309B: Swift-XRT refined Analysis
  97. IceCube Alert 250309.32: Global MASTER-Net observations report
  98. Fermi GRB 250307A: Global MASTER-Net observations report
  99. Fermi trigger No 762963055: Global MASTER-Net observations report
  100. LIGO/Virgo/KAGRA S250207bg: Update-5 NED Galaxies in the Localization Volume

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