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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 250430A: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
  2. GRB 250430A: SVOM/VT optical observations
  3. GRB 250430A: KAIT optical observations
  4. EP250428b: Pan-STARRS follow-up, upper limit on the optical counterpart, and possible host galaxy.
  5. GRB 250430A / EP250430a: J-band upper limits with WINTER
  6. GRB 250430A: NUTTelA-TAO Early Measurements
  7. EP250427a / GRB 250427A: OHP/T193 photometric observations: third visit
  8. GRB 250430A: DDOTI Optical Observations
  9. GRB 250430A: Leavitt Observatory optical upper limit
  10. GRB 250430A: Bassano Bresciano Observatory upper limit
  11. GRB 250430A : MITSuME Akeno optical upper limits
  12. GRB 250430A / EP250430a: VLT/X-shooter spectroscopic redshift z = 0.767
  13. SVOM/sb25043004: EP-FXT observations
  14. EP250430a/GRB 250430A: Einstein Probe WXT detection of the X-ray prompt emission
  15. GRB 250424A: CALET Gamma-Ray Burst Monitor detection
  16. IceCube-250429A: Upper limits from a search for additional neutrino events in IceCube
  17. IceCube-250426A: 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. GRB 250430A: Swift detection of a burst with optical counterpart
  22. Swift GRB250430.73: Global MASTER-Net observations report
  23. EP250428b: FTW optical and NIR observations
  24. EP250427a/GRB250427A: HCT optical follow-up
  25. EP250427a / GRB 250427A: OHP/T193 continued photometric observations
  26. SVOM/sb25043004: SVOM detection of a X-ray transient
  27. Fermi trigger No 767623859: Global MASTER-Net observations report
  28. EP250428b: refined analysis of the EP-FXT follow-up observation
  29. EP250428b: GROWTH-India telescope optical upper limit
  30. EP250428b: SVOM/VT upper limit
  31. EP250428b: SAO RAS optical upper limit
  32. EP250428b: LAST optical upper limit
  33. IceCube-250429A - IceCube observation of a high-energy neutrino candidate track-like event
  34. GRB 250427A: Swift/UVOT Detection
  35. EP250428b: Global MASTER-Net observations report
  36. EP250428b: Einstein Probe detection of a fast X-ray transient
  37. Fermi-LAT Gamma-ray Observations of IceCube-250426A
  38. EP250427a / GRB 250427A: OHP/T193 photometric observations
  39. EP250427a: EP-FXT follow-up observations
  40. EP250427a/GRB 250427A: FTW optical and NIR observations of the counterpart
  41. EP250427a: Lesedi optical counterpart detection
  42. EP250427A: COLIBRÍ Continuing Optical Observations
  43. GRB250427A/EP250427a GIT optical afterglow detection:
  44. EP250427a: LT optical counterpart detection
  45. GRB 250427A: Swift-XRT refined Analysis
  46. EP250427a / GRB 250427A: LCO optical counterpart detection
  47. EP250427a / GRB 250427A: VLT/X-shooter redshift confirmation z = 1.520
  48. EP250427A/GRB250427A: Keck/LRIS redshift
  49. EP250427a: REM optical/NIR afterglow detection
  50. GRB 250424A: LCO optical observation
  51. GRB 250427A/ EP250427a: Fermi-GBM Sub-Threshold Detection
  52. EP250427A: COLIBRÍ Optical Detection
  53. EP250427a: TRT optical counterpart detection
  54. EP 250427a: BOOTES-7 optical afterglow candidate
  55. EP250427a: Global MASTER-Net observations report
  56. EP250427a: Einstein Probe detection of a fast X-ray transient
  57. IceCube Alert 250426.74: Global MASTER-Net observations report
  58. GRB 250424A: Swift-BAT refined analysis
  59. IceCube-250426A - IceCube observation of a high-energy neutrino candidate track-like event (duplicate submission)
  60. IceCube-250426A - IceCube observation of a high-energy neutrino candidate track-like event
  61. GRB 250424A: SVOM/GRM observation of a long burst
  62. GRB 250424A: PRIME near-infrared detection
  63. GRB 250424A: WINTER J-band detection
  64. GRB 250424A: EIRSAT-1 GMOD Detection
  65. IceCube-250416A: Upper limits from a search for additional neutrino events in IceCube
  66. IceCube-250421A: Upper limits from a search for additional neutrino events in IceCube
  67. GRB 250424A: SVOM/VT optical observation
  68. GRB 250419A: Mondy Optical Observations
  69. GRB 250424A: Swift/UVOT Detection
  70. Konus-Wind detection of GRB 250424A
  71. Fermi-LAT gamma-ray observations of IceCube-250421A
  72. GRB 250424A: Skynet Optical Observations
  73. GRB 250424A: Kilonova-Catcher optical afterglow detection
  74. GRB 250419a: Continued Liverpool Telescope observations
  75. GRB 250419A: Liverpool Telescope optical upper limit
  76. GRB 250407A: GRBAlpha detection
  77. GRB 250404A / EP250404a: GRBAlpha detection
  78. GRB 250330B: GRBAlpha detection
  79. GRB 250419A: SVOM/ECLAIRs refined analysis
  80. GRB 250424A: Swift-XRT refined Analysis
  81. GRB 250424A: Enhanced Swift-XRT position
  82. GRB 250424A: AstroSat CZTI detection of a bright long burst
  83. GRB 250424A: COLIBRÍ Detection of a Bright Optical Counterpart
  84. GRB 250424A: BlackGEM optical afterglow detection
  85. GRB 250424A: VLT/X-shooter spectroscopic redshift z = 0.310
  86. GRB 250424A: likely host galaxy
  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 observations report
  91. Swift GRB 250424A: Global MASTER-Net OT detection
  92. LIGO/Virgo/KAGRA S250328ae: Subaru/PFS Spectroscopic Follow up and Candidates
  93. EP250421a: Nickel optical upper limit
  94. EP250416a / GRB 250416C: Gemini GMOS-S likely host galaxy redshift z = 0.963
  95. EP250421a: Upper limits from Fermi-GBM Observations
  96. SVOM/sb25042207: XRT observations
  97. SVOM/sb25042207: BOOTES-2 early optical upper limit
  98. SVOM/sb25042207: GOTO optical upper limits
  99. GRB 250421A: AstroSat CZTI detection
  100. SVOM/sb25042207: SVOM detection of an X-ray transient

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