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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"

24607 results found.

  1. GRB 250506A: SVOM detection of a burst
  2. GRB 250504A: Swift-BAT refined analysis
  3. GRB 250430A: Swift-BAT refined analysis
  4. GRB 250504A: Swift-XRT refined Analysis
  5. GRB 250504A: VLT/X-shooter upper limits
  6. GRB 250504A: REM optical/NIR observations
  7. GRB 250502A: REM optical/NIR observations
  8. GRB 250504A: MeerLICHT optical afterglow detection
  9. GRB 250504A: Fermi GBM Observation
  10. GRB 250504A: Enhanced Swift-XRT position
  11. Fermi GRB 250504A: Global MASTER-Net observations report
  12. GRB 250504A: Swift detection of a burst
  13. GRB 250502A: Swift/UVOT Follow up
  14. GRB 250502A: Mondy and Tien-Shan Optical Observations
  15. GRB 250502A: KAIT optical observations
  16. GRB 250502A: Montarrenti Observatory optical detection
  17. GRB 250502A: Swift-XRT afterglow detection
  18. GRB 250502A: NOT optical observations
  19. GRB 250502B: AstroSat CZTI detection
  20. GRB 250502A: AKO Optical Afterglow Detection
  21. GRB 250502A: LCO optical counterpart detection
  22. GRB 250502A: Redshift from OSIRIS+/GTC z = 2.163
  23. GRB 250407A: VZLUSAT-2 detection
  24. Fermi-LAT Gamma-ray Observations of IceCube-250429A
  25. GRB 250502B: DDOTI Optical Observations
  26. GRB 250430A: Swift-XRT refined Analysis
  27. GRB 250502A: Early optical counterpart detection by LCO.
  28. GRB 250430A: Swift/UVOT Detection
  29. GRB 250502A: TRT optical afterglow confirmation
  30. GRB 250430A: Enhanced Swift-XRT position
  31. GRB 250502A: SVOM/COLIBRÍ (FM-GFT) Detection of a Bright Optical Counterpart Candidate
  32. GRB 250502A: SVOM detection of a burst
  33. GRB 250430A: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
  34. GRB 250430A: KAIT optical observations
  35. GRB 250430A / EP250430a: J-band upper limits with WINTER
  36. GRB 250430A: NUTTelA-TAO Early Measurements
  37. GRB 250430A: DDOTI Optical Observations
  38. GRB 250430A: Leavitt Observatory optical upper limit
  39. GRB 250430A: Bassano Bresciano Observatory upper limit
  40. GRB 250430A : MITSuME Akeno optical upper limits
  41. SVOM/sb25043004: EP-FXT observations
  42. EP250430a/GRB 250430A: Einstein Probe WXT detection of the X-ray prompt emission
  43. GRB 250424A: CALET Gamma-Ray Burst Monitor detection
  44. IceCube-250429A: Upper limits from a search for additional neutrino events in IceCube
  45. IceCube-250426A: Upper limits from a search for additional neutrino events in IceCube
  46. GRB 250430A: AKO Optical Afterglow Detection
  47. GRB 250430A: Kanata optical upper limit
  48. EP 250427A: Optical counterpart detection by LCO.
  49. GRB 250430A: Swift detection of a burst with optical counterpart
  50. EP250427a/GRB250427A: HCT optical follow-up
  51. SVOM/sb25043004: SVOM detection of a X-ray transient
  52. EP250428b: GROWTH-India telescope optical upper limit
  53. EP250428b: SAO RAS optical upper limit
  54. EP250428b: LAST optical upper limit
  55. GRB 250427A: Swift/UVOT Detection
  56. EP250428b: Global MASTER-Net observations report
  57. EP250428b: Einstein Probe detection of a fast X-ray transient
  58. Fermi-LAT Gamma-ray Observations of IceCube-250426A
  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: REM optical/NIR afterglow detection
  66. GRB 250424A: LCO optical observation
  67. GRB 250427A/ EP250427a: Fermi-GBM Sub-Threshold Detection
  68. EP250427A: COLIBRÍ Optical Detection
  69. EP250427a: TRT optical counterpart detection
  70. EP250427a: Einstein Probe detection of a fast X-ray transient
  71. GRB 250424A: Swift-BAT refined analysis
  72. GRB 250424A: SVOM/GRM observation of a long burst
  73. GRB 250424A: PRIME near-infrared detection
  74. GRB 250424A: WINTER J-band detection
  75. GRB 250424A: EIRSAT-1 GMOD Detection
  76. IceCube-250416A: Upper limits from a search for additional neutrino events in IceCube
  77. IceCube-250421A: Upper limits from a search for additional neutrino events in IceCube
  78. GRB 250419A: Mondy Optical Observations
  79. GRB 250424A: Swift/UVOT Detection
  80. Fermi-LAT gamma-ray observations of IceCube-250421A
  81. GRB 250424A: Skynet Optical Observations
  82. GRB 250424A: Kilonova-Catcher optical afterglow detection
  83. GRB 250330B: GRBAlpha detection
  84. GRB 250424A: Swift-XRT refined Analysis
  85. GRB 250424A: Enhanced Swift-XRT position
  86. GRB 250424A: AstroSat CZTI detection of a bright long burst
  87. GRB 250424A: COLIBRÍ Detection of a Bright Optical Counterpart
  88. GRB 250424A: BlackGEM optical afterglow detection
  89. GRB 250424A: DDOTI Afterglow Detection
  90. GRB 250424A: REM optical/NIR afterglow detection
  91. GRB 250424A: Swift detection of a burst with an optical counterpart
  92. Swift GRB250424A: Global MASTER-Net OT detection
  93. LIGO/Virgo/KAGRA S250328ae: Subaru/PFS Spectroscopic Follow up and Candidates
  94. EP250421a: Nickel optical upper limit
  95. EP250421a: Upper limits from Fermi-GBM Observations
  96. SVOM/sb25042207: SVOM detection of an X-ray transient
  97. IceCube-250421A: DDOTI Detection of the LAST Candidate
  98. GRB 250419A: Mephisto Multi-band Optical Detection
  99. GRB 250419A: Calapai Observatory, Massa S. Giorgio (Messina), optical observations.
  100. IC-250421A: LAST optical observations of the IceCube neutrino candidate

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