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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"

24705 results found.

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

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