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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 250502A: LCO optical counterpart detection
  2. GRB 250502A: Swift ToO observations
  3. GRB 250502A: Redshift from OSIRIS+/GTC z = 2.163
  4. GRB 250502C: Fermi GBM Final Localization
  5. GRB 250407A: VZLUSAT-2 detection
  6. Fermi-LAT Gamma-ray Observations of IceCube-250429A
  7. GRB 250502B: DDOTI Optical Observations
  8. GRB 250430A: Swift-XRT refined Analysis
  9. GRB 250502A: Early optical counterpart detection by LCO.
  10. GRB 250430A: Swift/UVOT Detection
  11. GRB 250502A: SVOM/VT optical bump
  12. GRB 250502A: TRT optical afterglow confirmation
  13. GRB 250430A: Enhanced Swift-XRT position
  14. Fermi GRB 250502B: Global MASTER-Net observations report
  15. GRB 250430A: Optical Observations via Virtual Telescope Project, Italy
  16. GRB 250502A: SVOM/COLIBRÍ (FM-GFT) Detection of a Bright Optical Counterpart Candidate
  17. GRB 250502B: Fermi GBM Final Real-time Localization
  18. GRB 250502A: SVOM detection of a burst
  19. GRB 250430A: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
  20. GRB 250430A: SVOM/VT optical observations
  21. GRB 250430A: KAIT optical observations
  22. EP250428b: Pan-STARRS follow-up, upper limit on the optical counterpart, and possible host galaxy.
  23. GRB 250430A / EP250430a: J-band upper limits with WINTER
  24. GRB 250430A: NUTTelA-TAO Early Measurements
  25. EP250427a / GRB 250427A: OHP/T193 photometric observations: third visit
  26. GRB 250430A: DDOTI Optical Observations
  27. GRB 250430A: Leavitt Observatory optical upper limit
  28. GRB 250430A: Bassano Bresciano Observatory upper limit
  29. GRB 250430A : MITSuME Akeno optical upper limits
  30. GRB 250430A / EP250430a: VLT/X-shooter spectroscopic redshift z = 0.767
  31. SVOM/sb25043004: EP-FXT observations
  32. EP250430a/GRB 250430A: Einstein Probe WXT detection of the X-ray prompt emission
  33. GRB 250424A: CALET Gamma-Ray Burst Monitor detection
  34. IceCube-250429A: Upper limits from a search for additional neutrino events in IceCube
  35. IceCube-250426A: Upper limits from a search for additional neutrino events in IceCube
  36. GRB 250430A: AKO Optical Afterglow Detection
  37. GRB 250430A: Kanata optical upper limit
  38. EP 250427A: Optical counterpart detection by LCO.
  39. GRB 250430A: Swift detection of a burst with optical counterpart
  40. Swift GRB250430.73: Global MASTER-Net observations report
  41. EP250428b: FTW optical and NIR observations
  42. EP250427a/GRB250427A: HCT optical follow-up
  43. EP250427a / GRB 250427A: OHP/T193 continued photometric observations
  44. SVOM/sb25043004: SVOM detection of a X-ray transient
  45. Fermi trigger No 767623859: Global MASTER-Net observations report
  46. EP250428b: refined analysis of the EP-FXT follow-up observation
  47. EP250428b: GROWTH-India telescope optical upper limit
  48. EP250428b: SVOM/VT upper limit
  49. EP250428b: SAO RAS optical upper limit
  50. EP250428b: LAST optical upper limit
  51. IceCube-250429A - IceCube observation of a high-energy neutrino candidate track-like event
  52. GRB 250427A: Swift/UVOT Detection
  53. EP250428b: Global MASTER-Net observations report
  54. EP250428b: Einstein Probe detection of a fast X-ray transient
  55. Fermi-LAT Gamma-ray Observations of IceCube-250426A
  56. EP250427a / GRB 250427A: OHP/T193 photometric observations
  57. EP250427a: EP-FXT follow-up observations
  58. EP250427a/GRB 250427A: FTW optical and NIR observations of the counterpart
  59. EP250427a: Lesedi optical counterpart detection
  60. EP250427A: COLIBRÍ Continuing Optical Observations
  61. GRB250427A/EP250427a GIT optical afterglow detection:
  62. EP250427a: LT optical counterpart detection
  63. GRB 250427A: Swift-XRT refined Analysis
  64. EP250427a / GRB 250427A: LCO optical counterpart detection
  65. EP250427a / GRB 250427A: VLT/X-shooter redshift confirmation z = 1.520
  66. EP250427A/GRB250427A: Keck/LRIS redshift
  67. EP250427a: REM optical/NIR afterglow detection
  68. GRB 250424A: LCO optical observation
  69. GRB 250427A/ EP250427a: Fermi-GBM Sub-Threshold Detection
  70. EP250427A: COLIBRÍ Optical Detection
  71. EP250427a: TRT optical counterpart detection
  72. EP 250427a: BOOTES-7 optical afterglow candidate
  73. EP250427a: Global MASTER-Net observations report
  74. EP250427a: Einstein Probe detection of a fast X-ray transient
  75. IceCube Alert 250426.74: Global MASTER-Net observations report
  76. GRB 250424A: Swift-BAT refined analysis
  77. IceCube-250426A - IceCube observation of a high-energy neutrino candidate track-like event (duplicate submission)
  78. IceCube-250426A - IceCube observation of a high-energy neutrino candidate track-like event
  79. GRB 250424A: SVOM/GRM observation of a long burst
  80. GRB 250424A: PRIME near-infrared detection
  81. GRB 250424A: WINTER J-band detection
  82. GRB 250424A: EIRSAT-1 GMOD Detection
  83. IceCube-250416A: Upper limits from a search for additional neutrino events in IceCube
  84. IceCube-250421A: Upper limits from a search for additional neutrino events in IceCube
  85. GRB 250424A: SVOM/VT optical observation
  86. GRB 250419A: Mondy Optical Observations
  87. GRB 250424A: Swift/UVOT Detection
  88. Konus-Wind detection of GRB 250424A
  89. Fermi-LAT gamma-ray observations of IceCube-250421A
  90. GRB 250424A: Skynet Optical Observations
  91. GRB 250424A: Kilonova-Catcher optical afterglow detection
  92. GRB 250419a: Continued Liverpool Telescope observations
  93. GRB 250419A: Liverpool Telescope optical upper limit
  94. GRB 250407A: GRBAlpha detection
  95. GRB 250404A / EP250404a: GRBAlpha detection
  96. GRB 250330B: GRBAlpha detection
  97. GRB 250419A: SVOM/ECLAIRs refined analysis
  98. GRB 250424A: Swift-XRT refined Analysis
  99. GRB 250424A: Enhanced Swift-XRT position
  100. GRB 250424A: AstroSat CZTI detection of a bright long burst

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