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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"
  1. GRB 250502C: Fermi GBM Final Localization
  2. GRB 250407A: VZLUSAT-2 detection
  3. Fermi-LAT Gamma-ray Observations of IceCube-250429A
  4. GRB 250502B: DDOTI Optical Observations
  5. GRB 250430A: Swift-XRT refined Analysis
  6. GRB 250502A: Early optical counterpart detection by LCO.
  7. GRB 250430A: Swift/UVOT Detection
  8. GRB 250502A: SVOM/VT optical bump
  9. GRB 250502A: TRT optical afterglow confirmation
  10. GRB 250430A: Enhanced Swift-XRT position
  11. Fermi GRB 250502B: Global MASTER-Net observations report
  12. GRB 250430A: Optical Observations via Virtual Telescope Project, Italy
  13. GRB 250502A: SVOM/COLIBRÍ (FM-GFT) Detection of a Bright Optical Counterpart Candidate
  14. GRB 250502B: Fermi GBM Final Real-time Localization
  15. GRB 250502A: SVOM detection of a burst
  16. GRB 250430A: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
  17. GRB 250430A: SVOM/VT optical observations
  18. GRB 250430A: KAIT optical observations
  19. EP250428b: Pan-STARRS follow-up, upper limit on the optical counterpart, and possible host galaxy.
  20. GRB 250430A / EP250430a: J-band upper limits with WINTER
  21. GRB 250430A: NUTTelA-TAO Early Measurements
  22. EP250427a / GRB 250427A: OHP/T193 photometric observations: third visit
  23. GRB 250430A: DDOTI Optical Observations
  24. GRB 250430A: Leavitt Observatory optical upper limit
  25. GRB 250430A: Bassano Bresciano Observatory upper limit
  26. GRB 250430A : MITSuME Akeno optical upper limits
  27. GRB 250430A / EP250430a: VLT/X-shooter spectroscopic redshift z = 0.767
  28. SVOM/sb25043004: EP-FXT observations
  29. EP250430a/GRB 250430A: Einstein Probe WXT detection of the X-ray prompt emission
  30. GRB 250424A: CALET Gamma-Ray Burst Monitor detection
  31. IceCube-250429A: Upper limits from a search for additional neutrino events in IceCube
  32. IceCube-250426A: Upper limits from a search for additional neutrino events in IceCube
  33. GRB 250430A: AKO Optical Afterglow Detection
  34. GRB 250430A: Kanata optical upper limit
  35. EP 250427A: Optical counterpart detection by LCO.
  36. GRB 250430A: Swift detection of a burst with optical counterpart
  37. Swift GRB250430.73: Global MASTER-Net observations report
  38. EP250428b: FTW optical and NIR observations
  39. EP250427a/GRB250427A: HCT optical follow-up
  40. EP250427a / GRB 250427A: OHP/T193 continued photometric observations
  41. SVOM/sb25043004: SVOM detection of a X-ray transient
  42. Fermi trigger No 767623859: Global MASTER-Net observations report
  43. EP250428b: refined analysis of the EP-FXT follow-up observation
  44. EP250428b: GROWTH-India telescope optical upper limit
  45. EP250428b: SVOM/VT upper limit
  46. EP250428b: SAO RAS optical upper limit
  47. EP250428b: LAST optical upper limit
  48. IceCube-250429A - IceCube observation of a high-energy neutrino candidate track-like event
  49. GRB 250427A: Swift/UVOT Detection
  50. EP250428b: Global MASTER-Net observations report
  51. EP250428b: Einstein Probe detection of a fast X-ray transient
  52. Fermi-LAT Gamma-ray Observations of IceCube-250426A
  53. EP250427a / GRB 250427A: OHP/T193 photometric observations
  54. EP250427a: EP-FXT follow-up observations
  55. EP250427a/GRB 250427A: FTW optical and NIR observations of the counterpart
  56. EP250427a: Lesedi optical counterpart detection
  57. EP250427A: COLIBRÍ Continuing Optical Observations
  58. GRB250427A/EP250427a GIT optical afterglow detection:
  59. EP250427a: LT optical counterpart detection
  60. GRB 250427A: Swift-XRT refined Analysis
  61. EP250427a / GRB 250427A: LCO optical counterpart detection
  62. EP250427a / GRB 250427A: VLT/X-shooter redshift confirmation z = 1.520
  63. EP250427A/GRB250427A: Keck/LRIS redshift
  64. EP250427a: REM optical/NIR afterglow detection
  65. GRB 250424A: LCO optical observation
  66. GRB 250427A/ EP250427a: Fermi-GBM Sub-Threshold Detection
  67. EP250427A: COLIBRÍ Optical Detection
  68. EP250427a: TRT optical counterpart detection
  69. EP 250427a: BOOTES-7 optical afterglow candidate
  70. EP250427a: Global MASTER-Net observations report
  71. EP250427a: Einstein Probe detection of a fast X-ray transient
  72. IceCube Alert 250426.74: Global MASTER-Net observations report
  73. GRB 250424A: Swift-BAT refined analysis
  74. IceCube-250426A - IceCube observation of a high-energy neutrino candidate track-like event (duplicate submission)
  75. IceCube-250426A - IceCube observation of a high-energy neutrino candidate track-like event
  76. GRB 250424A: SVOM/GRM observation of a long burst
  77. GRB 250424A: PRIME near-infrared detection
  78. GRB 250424A: WINTER J-band detection
  79. GRB 250424A: EIRSAT-1 GMOD Detection
  80. IceCube-250416A: Upper limits from a search for additional neutrino events in IceCube
  81. IceCube-250421A: Upper limits from a search for additional neutrino events in IceCube
  82. GRB 250424A: SVOM/VT optical observation
  83. GRB 250419A: Mondy Optical Observations
  84. GRB 250424A: Swift/UVOT Detection
  85. Konus-Wind detection of GRB 250424A
  86. Fermi-LAT gamma-ray observations of IceCube-250421A
  87. GRB 250424A: Skynet Optical Observations
  88. GRB 250424A: Kilonova-Catcher optical afterglow detection
  89. GRB 250419a: Continued Liverpool Telescope observations
  90. GRB 250419A: Liverpool Telescope optical upper limit
  91. GRB 250407A: GRBAlpha detection
  92. GRB 250404A / EP250404a: GRBAlpha detection
  93. GRB 250330B: GRBAlpha detection
  94. GRB 250419A: SVOM/ECLAIRs refined analysis
  95. GRB 250424A: Swift-XRT refined Analysis
  96. GRB 250424A: Enhanced Swift-XRT position
  97. GRB 250424A: AstroSat CZTI detection of a bright long burst
  98. GRB 250424A: COLIBRÍ Detection of a Bright Optical Counterpart
  99. GRB 250424A: BlackGEM optical afterglow detection
  100. GRB 250424A: VLT/X-shooter spectroscopic redshift z = 0.310

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