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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 250502B: DDOTI Optical Observations
  2. GRB 250430A: Swift-XRT refined Analysis
  3. GRB 250502A: Early optical counterpart detection by LCO.
  4. GRB 250502A: TRT optical afterglow confirmation
  5. GRB 250430A: Enhanced Swift-XRT position
  6. Fermi GRB 250502B: Global MASTER-Net observations report
  7. GRB 250502B: Fermi GBM Final Real-time Localization
  8. EP250428b: Pan-STARRS follow-up, upper limit on the optical counterpart, and possible host galaxy.
  9. GRB 250430A / EP250430a: J-band upper limits with WINTER
  10. GRB 250430A: Leavitt Observatory optical upper limit
  11. GRB 250430A: Bassano Bresciano Observatory upper limit
  12. GRB 250430A : MITSuME Akeno optical upper limits
  13. GRB 250430A / EP250430a: VLT/X-shooter spectroscopic redshift z = 0.767
  14. SVOM/sb25043004: EP-FXT observations
  15. EP250430a/GRB 250430A: Einstein Probe WXT detection of the X-ray prompt emission
  16. GRB 250424A: CALET Gamma-Ray Burst Monitor detection
  17. IceCube-250429A: Upper limits from a search for additional neutrino events in IceCube
  18. GRB 250430A: AKO Optical Afterglow Detection
  19. GRB 250430A: Kanata optical upper limit
  20. EP 250427A: Optical counterpart detection by LCO.
  21. Swift GRB250430.73: Global MASTER-Net observations report
  22. EP250427a/GRB250427A: HCT optical follow-up
  23. Fermi trigger No 767623859: Global MASTER-Net observations report
  24. EP250428b: refined analysis of the EP-FXT follow-up observation
  25. EP250428b: GROWTH-India telescope optical upper limit
  26. EP250428b: LAST optical upper limit
  27. IceCube-250429A - IceCube observation of a high-energy neutrino candidate track-like event
  28. Fermi-LAT Gamma-ray Observations of IceCube-250426A
  29. EP250427A: COLIBRÍ Continuing Optical Observations
  30. EP250427a: LT optical counterpart detection
  31. GRB 250427A: Swift-XRT refined Analysis
  32. EP250427a / GRB 250427A: LCO optical counterpart detection
  33. GRB 250424A: LCO optical observation
  34. GRB 250427A/ EP250427a: Fermi-GBM Sub-Threshold Detection
  35. EP250427a: TRT optical counterpart detection
  36. EP250427a: Einstein Probe detection of a fast X-ray transient
  37. IceCube Alert 250426.74: Global MASTER-Net observations report
  38. GRB 250424A: SVOM/GRM observation of a long burst
  39. GRB 250424A: WINTER J-band detection
  40. GRB 250424A: EIRSAT-1 GMOD Detection
  41. IceCube-250416A: Upper limits from a search for additional neutrino events in IceCube
  42. IceCube-250421A: Upper limits from a search for additional neutrino events in IceCube
  43. GRB 250424A: Skynet Optical Observations
  44. GRB 250424A: Kilonova-Catcher optical afterglow detection
  45. GRB 250404A / EP250404a: GRBAlpha detection
  46. GRB 250330B: GRBAlpha detection
  47. GRB 250419A: SVOM/ECLAIRs refined analysis
  48. GRB 250424A: Enhanced Swift-XRT position
  49. GRB 250424A: AstroSat CZTI detection of a bright long burst
  50. GRB 250424A: VLT/X-shooter spectroscopic redshift z = 0.310
  51. GRB 250424A: DDOTI Afterglow Detection
  52. GRB 250424A: REM optical/NIR afterglow detection
  53. GRB 250424A: Swift detection of a burst with an optical counterpart
  54. Swift GRB 250424A: Global MASTER-Net observations report
  55. LIGO/Virgo/KAGRA S250328ae: Subaru/PFS Spectroscopic Follow up and Candidates
  56. EP250416a / GRB 250416C: Gemini GMOS-S likely host galaxy redshift z = 0.963
  57. SVOM/sb25042207: XRT observations
  58. SVOM/sb25042207: BOOTES-2 early optical upper limit
  59. GRB 250421A: AstroSat CZTI detection
  60. SVOM/sb25042207: SVOM detection of an X-ray transient
  61. IceCube-250421A: DDOTI Detection of the LAST Candidate
  62. IC-250421A: LAST optical observations of the IceCube neutrino candidate
  63. GRB 250419A: Optical Observations via Virtual Telescope Project
  64. EP250421a: REM optical upper limit
  65. EP250421a: Swift/XRT counterpart detection
  66. GRB 250419A: Mondy Continued Optical Observations
  67. IceCube-Cascade 250414A: Upper limits from a search for additional neutrino events in IceCube
  68. The EP-WXT trigger 01709135179: Kinder optical counterpart candidate
  69. GRB 250421A: Fermi GBM Final Real-time Localization
  70. GRB 250419A: Liverpool Telescope observations
  71. GRB 250419A: LCO optical observation
  72. GRB 250419A: SVOM/C-GFT optical observations
  73. GRB 250416C / EP250416a: SVOM/GRM observation of a burst
  74. GRB 250419A: LCO optical afterglow multi-band observations
  75. GRB 250419A: Liverpool Telescope observations
  76. GRB 250419A: AKO Optical Afterglow Detection
  77. GRB 250419A: MASTER optical afterglow observation
  78. Fermi-LAT Gamma-ray Observations of IceCube-250416A
  79. GRB 250419A: Swift-XRT localisation
  80. GRB 250407A: GTC/OSIRIS+ spectroscopic redshift z = 1.36
  81. GRB 250419A: Swift-XRT refined Analysis
  82. GRB 250419A: KAIT optical afterglow observations
  83. GRB 250419A: SVOM/COLIBRÍ (FM-GFT) Detection of the Optical Counterpart
  84. GRB 250419A: SVOM detection of a soft burst
  85. EP250416a: Swift/XRT counterpart fading
  86. Konus-Wind detection of GRB 250403A
  87. EP20250416a: Swift/XRT counterpart detection
  88. GRB 250403A: VLT/FORS2 spectroscopic redshift z = 1.847
  89. EP250225a: SVOM/VT optical brightening
  90. EP250416a: GSP optical upper limit
  91. EP250416a: Global MASTER-Net observations report
  92. Fermi Gamma-ray Burst Monitor trigger 766505186/250416588 (GRB 250416A) is not a GRB
  93. IceCube-250416A - IceCube observation of a high-energy neutrino candidate track-like event
  94. GRB 250416B: Fermi GBM Final Real-time Localization
  95. GRB 250416A: Fermi GBM Final Real-time Localization
  96. SVOM/sb25041603: SVOM detection of an X-ray transient
  97. Fermi Gamma-ray Burst Monitor trigger 766474855/250416237 is not a GRB
  98. IceCube 250414.324: DDOTI Optical Observations
  99. GRB 250413A: AstroSat CZTI detection
  100. EP250304a: ATCA radio observations

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