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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"

23838 results found.

  1. EP250416a: Swift/XRT counterpart fading
  2. EP250416a: refined EP-WXT and EP-FXT analysis
  3. EP20250416a: Swift/XRT counterpart detection
  4. IceCube-250416A: DDOTI Optical Observations
  5. SVOM/sb25041603 is not a GRB
  6. EP250416a: GSP optical upper limit
  7. EP250416a: Global MASTER-Net observations report
  8. Fermi Gamma-ray Burst Monitor trigger 766505186/250416588 (GRB 250416A) is not a GRB
  9. IceCube-250416A: Global MASTER-Net observations report
  10. Fermi Gamma-ray Burst Monitor trigger 766511207/250416657 is not a GRB
  11. GRB 250416B: Fermi GBM Final Real-time Localization
  12. GRB 250416A: Fermi GBM Final Real-time Localization
  13. SVOM/sb25041603: SVOM/COLIBRÍ (FM-GFT) Upper Limit on the Optical Counterpart
  14. SVOM/sb25041603: SVOM detection of an X-ray transient
  15. Fermi Gamma-ray Burst Monitor trigger 766474855/250416237 is not a GRB
  16. IceCube 250414.324: DDOTI Optical Observations
  17. EP250304a: ATCA radio observations
  18. GRB 250412A: AstroSat CZTI detection
  19. EP250404a: Nanshan 0.43m Telescope optical observatios
  20. Fermi trigger No 766148493: Global MASTER-Net observations report
  21. Fermi trigger No 766173972: Global MASTER-Net observations report
  22. GRB 250411A: DDOTI Optical Observations
  23. Fermi GRB 250411A: Global MASTER-Net observations report
  24. GRB 250411A: Fermi GBM Final Real-time Localization
  25. GRB 250407A: Mondy and AbAO Optical Observations
  26. EP250227a: Further NOT optical observations
  27. IceCube-250406A: Swift-XRT observations
  28. IPN triangulation of GRB 250407A
  29. EP250407a: Global MASTER-Net observations report
  30. GRB 250407A: LCO detection of a fading optical counterpart
  31. GRB 250407A: SVOM/GRM observation of a bright long burst
  32. GRB 250407A: EP-WXT afterglow detection
  33. EP250407a: EP-WXT detection of a fast X-ray transient
  34. GRB 250407A: COLIBRÍ/DDRAGO Detection of the Optical Counterpart
  35. GRB 250407A: Fermi GBM Detection
  36. Fermi GRB 250407A: Global MASTER-Net observations report
  37. LIGO/Virgo/KAGRA S250331o: Upper limits from Swift/BAT-GUANO
  38. IceCube 250406A: DDOTI Optical Observations of the Refined Position
  39. IPN triangulation of GRB 250406B (short/hard)
  40. GRB 250407A: BALROG localization (Fermi Trigger 765733706 / GRB 250407659)
  41. GRB 250407A: Fermi GBM Final Real-time Localization
  42. IceCube 250406.951: COLIBRÍ/DDRAGO Optical Upper Limit
  43. IceCube 250406.951: DDOTI Optical Observations
  44. IceCube Alert 250406.95: Global MASTER-Net observations report
  45. Fermi trigger No 765663719: Global MASTER-Net observations report
  46. Fermi GRB 250406A: Global MASTER-Net observations report
  47. GRB 250406A: Fermi GBM Final Real-time Localization
  48. EP250404a / GRB 250404A: Montarrenti Observatory optical observations
  49. Fermi trigger No 765619921: Global MASTER-Net observations report
  50. Fermi Gamma-ray Burst Monitor trigger 765619921/250406342 is not a GRB
  51. EP250404a / GRB 250404A: J band observations by SYSU 80cm telescope
  52. GRB 250404A / EP250404a: GMG spectroscopic redshift at z ~ 2.627
  53. GRB 250404A / EP250404a: Leavitt Observatory optical counterpart detection
  54. EP250402a: Optical upper limit with PD 1.3m observations
  55. GRB 250404A / EP250404a: NOT optical observations
  56. GRB 250331D: Swift-XRT afterglow detection
  57. EP250404a: Osservatorio Astronomico "Nastro Verde" optical observations: detection of an optical counterpart
  58. EP250404a: REM optical/NIR observations
  59. EP250404A: COLIBRÍ/DDRAGO Optical Observations
  60. EP250404A / GRB250404A: Ondrejov D50 optical afterglow detection
  61. EP250404a: LCO optical counterpart detection
  62. Fermi GRB 250404A: Global MASTER-Net observations report
  63. EP250404a: Xinglong decaying optical counterpart
  64. GRB 250404A: Fermi GBM Detection
  65. EP250404a: Global MASTER-Net observations report
  66. GRB 250403A: KAIT optical observations
  67. EP250404a: AKO Optical Afterglow Detection
  68. GRB 250402A: Swift/BAT-GUANO localization skymap of a burst
  69. GRB 250403A: Fermi GBM observations
  70. EP250404a: Mephisto multi-band optical detection
  71. GRB 250331C Swift-BAT refined analysis
  72. GRB 250331B Swift-BAT refined analysis
  73. GRB 250330A Swift-BAT refined analysis
  74. EP250321A: J band upper limit by SYSU 80cm telescope
  75. EP250404a: Nanshan/HMT optical counterpart detection
  76. GRB 250404A: Fermi GBM Final Real-time Localization
  77. EP250402a: Optical upper limit with Kinder observations
  78. GRB 250403A: REM NIR afterglow detection
  79. IceCube-250330A: MASTER detection of PKS 2032+107 blazar flare with Zhirkov effect
  80. GRB 250403A: JinShan optical observations
  81. GRB 250403A: Optical counterpart detection by LCO.
  82. EP250402a: EP-FXT follow-up observations
  83. GRB 250403A: Swift-XRT observations
  84. Fermi GRB 250403A: Global MASTER-Net observations report
  85. GRB 250402A: NUTTelA-TAO Early Optical Limits
  86. GRB 250403A: GMG Optical Observation
  87. GRB 250403A: 1.6m Mephisto multi-band optical detection
  88. GRB 250402A: Fermi GBM Observation
  89. GRB 250403A: SVOM/C-GFT optical observations
  90. GRB 250403A: GOTO detection of the optical afterglow
  91. GRB 250402A: Swift-XRT observations
  92. GRB 250403A : SVOM detection of a burst
  93. GRB 250403A: Fermi GBM Final Real-time Localization
  94. GRB 250225B: VLT host galaxy redshift z = 0.950
  95. GRB250402A: SVOM/COLIBRÍ (FM-GFT) Detection of the Optical Counterpart
  96. GRB 250402A: VLT/FORS2 spectroscopic redshift z = 2.823
  97. GRB 250402A: REM optical/NIR upper limits
  98. GRB 250402A: LCO optical counterpart detection
  99. GRB 250402A: refined SVOM/MXT data analysis
  100. The EP-WXT trigger 01709133862 is a flaring star

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