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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"

24978 results found.

  1. GRB 250430A: Enhanced Swift-XRT position
  2. GRB 250502A: SVOM/COLIBRÍ (FM-GFT) Detection of a Bright Optical Counterpart Candidate
  3. GRB 250502A: SVOM detection of a burst
  4. GRB 250430A: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
  5. GRB 250430A: KAIT optical observations
  6. GRB 250430A / EP250430a: J-band upper limits with WINTER
  7. GRB 250430A: NUTTelA-TAO Early Measurements
  8. GRB 250430A: DDOTI Optical Observations
  9. GRB 250430A: Leavitt Observatory optical upper limit
  10. GRB 250430A: Bassano Bresciano Observatory upper limit
  11. GRB 250430A : MITSuME Akeno optical upper limits
  12. SVOM/sb25043004: EP-FXT observations
  13. EP250430a/GRB 250430A: Einstein Probe WXT detection of the X-ray prompt emission
  14. GRB 250424A: CALET Gamma-Ray Burst Monitor detection
  15. IceCube-250429A: Upper limits from a search for additional neutrino events in IceCube
  16. IceCube-250426A: Upper limits from a search for additional neutrino events in IceCube
  17. GRB 250430A: AKO Optical Afterglow Detection
  18. GRB 250430A: Kanata optical upper limit
  19. EP 250427A: Optical counterpart detection by LCO.
  20. GRB 250430A: Swift detection of a burst with optical counterpart
  21. EP250427a/GRB250427A: HCT optical follow-up
  22. SVOM/sb25043004: SVOM detection of a X-ray transient
  23. EP250428b: GROWTH-India telescope optical upper limit
  24. EP250428b: SAO RAS optical upper limit
  25. EP250428b: LAST optical upper limit
  26. GRB 250427A: Swift/UVOT Detection
  27. EP250428b: Global MASTER-Net observations report
  28. EP250428b: Einstein Probe detection of a fast X-ray transient
  29. Fermi-LAT Gamma-ray Observations of IceCube-250426A
  30. EP250427a: Lesedi optical counterpart detection
  31. EP250427A: COLIBRÍ Continuing Optical Observations
  32. GRB250427A/EP250427a GIT optical afterglow detection:
  33. EP250427a: LT optical counterpart detection
  34. GRB 250427A: Swift-XRT refined Analysis
  35. EP250427a / GRB 250427A: LCO optical counterpart detection
  36. EP250427a: REM optical/NIR afterglow detection
  37. GRB 250424A: LCO optical observation
  38. GRB 250427A/ EP250427a: Fermi-GBM Sub-Threshold Detection
  39. EP250427A: COLIBRÍ Optical Detection
  40. EP250427a: TRT optical counterpart detection
  41. EP250427a: Einstein Probe detection of a fast X-ray transient
  42. GRB 250424A: Swift-BAT refined analysis
  43. GRB 250424A: SVOM/GRM observation of a long burst
  44. GRB 250424A: PRIME near-infrared detection
  45. GRB 250424A: WINTER J-band detection
  46. GRB 250424A: EIRSAT-1 GMOD Detection
  47. IceCube-250416A: Upper limits from a search for additional neutrino events in IceCube
  48. IceCube-250421A: Upper limits from a search for additional neutrino events in IceCube
  49. GRB 250419A: Mondy Optical Observations
  50. GRB 250424A: Swift/UVOT Detection
  51. Fermi-LAT gamma-ray observations of IceCube-250421A
  52. GRB 250424A: Skynet Optical Observations
  53. GRB 250424A: Kilonova-Catcher optical afterglow detection
  54. GRB 250330B: GRBAlpha detection
  55. GRB 250424A: Swift-XRT refined Analysis
  56. GRB 250424A: Enhanced Swift-XRT position
  57. GRB 250424A: AstroSat CZTI detection of a bright long burst
  58. GRB 250424A: COLIBRÍ Detection of a Bright Optical Counterpart
  59. GRB 250424A: BlackGEM optical afterglow detection
  60. GRB 250424A: DDOTI Afterglow Detection
  61. GRB 250424A: REM optical/NIR afterglow detection
  62. GRB 250424A: Swift detection of a burst with an optical counterpart
  63. Swift GRB 250424A: Global MASTER-Net OT detection
  64. LIGO/Virgo/KAGRA S250328ae: Subaru/PFS Spectroscopic Follow up and Candidates
  65. EP250421a: Nickel optical upper limit
  66. EP250421a: Upper limits from Fermi-GBM Observations
  67. SVOM/sb25042207: SVOM detection of an X-ray transient
  68. IceCube-250421A: DDOTI Detection of the LAST Candidate
  69. GRB 250419A: Mephisto Multi-band Optical Detection
  70. GRB 250419A: Calapai Observatory, Massa S. Giorgio (Messina), optical observations.
  71. IC-250421A: LAST optical observations of the IceCube neutrino candidate
  72. EP250421a: NOT optical observations
  73. GRB 250419A: Optical Observations via Virtual Telescope Project
  74. EP250421a: REM optical upper limit
  75. EP250421A: COLIBRÍ Optical Upper Limit
  76. GRB 250419A: Mondy Continued Optical Observations
  77. GRB 250421B: AstroSat CZTI detection of a bright long burst
  78. EP250421a: Einstein Probe detection of an X-ray transient
  79. EP250421a: Mephisto optical counterpart confirmation
  80. IceCube-Cascade 250414A: Upper limits from a search for additional neutrino events in IceCube
  81. EP250421a: JinShan likely optical counterpart
  82. The EP-WXT trigger 01709135179: Kinder optical counterpart candidate
  83. GRB 250419A: LCO optical observation
  84. GRB 250419A: JinShan optical observations
  85. GRB 250419A: SVOM/C-GFT optical observations
  86. GRB 250419A: Swift/UVOT Follow up
  87. GRB 250416C / EP250416a: SVOM/GRM observation of a burst
  88. GRB 250419A: LCO optical afterglow multi-band observations
  89. GRB 250419A: Mondy and AbAO Optical Observations
  90. GRB 250419A: AKO Optical Afterglow Detection
  91. Fermi-LAT Gamma-ray Observations of IceCube-250416A
  92. GRB 250419A: Swift-XRT refined Analysis
  93. GRB 250419A: KAIT optical afterglow observations
  94. GRB 250419A: SVOM/VT optical bright counterpart confirmation
  95. GRB 250419A: SVOM/COLIBRÍ (FM-GFT) Detection of the Optical Counterpart
  96. GRB 250419A: SVOM detection of a soft burst
  97. EP250416a: Swift/XRT counterpart fading
  98. EP20250416a: Swift/XRT counterpart detection
  99. IceCube-250416A: DDOTI Optical Observations
  100. EP250416a: Gemini South-GMOS optical counterpart

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