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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 / EP250430a: J-band upper limits with WINTER
  2. GRB 250430A: NUTTelA-TAO Early Measurements
  3. EP250427a / GRB 250427A: OHP/T193 photometric observations: third visit
  4. GRB 250430A: DDOTI Optical Observations
  5. GRB 250430A: Leavitt Observatory optical upper limit
  6. GRB 250430A: Bassano Bresciano Observatory upper limit
  7. GRB 250430A : MITSuME Akeno optical upper limits
  8. GRB 250430A / EP250430a: VLT/X-shooter spectroscopic redshift z = 0.767
  9. SVOM/sb25043004: EP-FXT observations
  10. EP250430a/GRB 250430A: Einstein Probe WXT detection of the X-ray prompt emission
  11. GRB 250424A: CALET Gamma-Ray Burst Monitor detection
  12. IceCube-250429A: Upper limits from a search for additional neutrino events in IceCube
  13. IceCube-250426A: Upper limits from a search for additional neutrino events in IceCube
  14. GRB 250430A: AKO Optical Afterglow Detection
  15. GRB 250430A: Kanata optical upper limit
  16. EP 250427A: Optical counterpart detection by LCO.
  17. GRB 250430A: Swift detection of a burst with optical counterpart
  18. Swift GRB250430.73: Global MASTER-Net observations report
  19. EP250428b: FTW optical and NIR observations
  20. EP250427a/GRB250427A: HCT optical follow-up
  21. EP250427a / GRB 250427A: OHP/T193 continued photometric observations
  22. SVOM/sb25043004: SVOM detection of a X-ray transient
  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: SVOM/VT upper limit
  27. EP250428b: SAO RAS optical upper limit
  28. EP250428b: LAST optical upper limit
  29. IceCube-250429A - IceCube observation of a high-energy neutrino candidate track-like event
  30. GRB 250427A: Swift/UVOT Detection
  31. EP250428b: Global MASTER-Net observations report
  32. EP250428b: Einstein Probe detection of a fast X-ray transient
  33. Fermi-LAT Gamma-ray Observations of IceCube-250426A
  34. EP250427a / GRB 250427A: OHP/T193 photometric observations
  35. EP250427a: EP-FXT follow-up observations
  36. EP250427a/GRB 250427A: FTW optical and NIR observations of the counterpart
  37. EP250427a: Lesedi optical counterpart detection
  38. EP250427A: COLIBRÍ Continuing Optical Observations
  39. GRB250427A/EP250427a GIT optical afterglow detection:
  40. EP250427a: LT optical counterpart detection
  41. GRB 250427A: Swift-XRT refined Analysis
  42. EP250427a / GRB 250427A: LCO optical counterpart detection
  43. EP250427a / GRB 250427A: VLT/X-shooter redshift confirmation z = 1.520
  44. EP250427A/GRB250427A: Keck/LRIS redshift
  45. EP250427a: REM optical/NIR afterglow detection
  46. GRB 250424A: LCO optical observation
  47. GRB 250427A/ EP250427a: Fermi-GBM Sub-Threshold Detection
  48. EP250427A: COLIBRÍ Optical Detection
  49. EP250427a: TRT optical counterpart detection
  50. EP 250427a: BOOTES-7 optical afterglow candidate
  51. EP250427a: Global MASTER-Net observations report
  52. EP250427a: Einstein Probe detection of a fast X-ray transient
  53. IceCube Alert 250426.74: Global MASTER-Net observations report
  54. GRB 250424A: Swift-BAT refined analysis
  55. IceCube-250426A - IceCube observation of a high-energy neutrino candidate track-like event (duplicate submission)
  56. IceCube-250426A - IceCube observation of a high-energy neutrino candidate track-like event
  57. GRB 250424A: SVOM/GRM observation of a long burst
  58. GRB 250424A: PRIME near-infrared detection
  59. GRB 250424A: WINTER J-band detection
  60. GRB 250424A: EIRSAT-1 GMOD Detection
  61. IceCube-250416A: Upper limits from a search for additional neutrino events in IceCube
  62. IceCube-250421A: Upper limits from a search for additional neutrino events in IceCube
  63. GRB 250424A: SVOM/VT optical observation
  64. GRB 250419A: Mondy Optical Observations
  65. GRB 250424A: Swift/UVOT Detection
  66. Konus-Wind detection of GRB 250424A
  67. Fermi-LAT gamma-ray observations of IceCube-250421A
  68. GRB 250424A: Skynet Optical Observations
  69. GRB 250424A: Kilonova-Catcher optical afterglow detection
  70. GRB 250419a: Continued Liverpool Telescope observations
  71. GRB 250419A: Liverpool Telescope optical upper limit
  72. GRB 250407A: GRBAlpha detection
  73. GRB 250404A / EP250404a: GRBAlpha detection
  74. GRB 250330B: GRBAlpha detection
  75. GRB 250419A: SVOM/ECLAIRs refined analysis
  76. GRB 250424A: Swift-XRT refined Analysis
  77. GRB 250424A: Enhanced Swift-XRT position
  78. GRB 250424A: AstroSat CZTI detection of a bright long burst
  79. GRB 250424A: COLIBRÍ Detection of a Bright Optical Counterpart
  80. GRB 250424A: BlackGEM optical afterglow detection
  81. GRB 250424A: VLT/X-shooter spectroscopic redshift z = 0.310
  82. GRB 250424A: likely host galaxy
  83. GRB 250424A: DDOTI Afterglow Detection
  84. GRB 250424A: REM optical/NIR afterglow detection
  85. GRB 250424A: Swift detection of a burst with an optical counterpart
  86. Swift GRB 250424A: Global MASTER-Net observations report
  87. Swift GRB 250424A: Global MASTER-Net OT detection
  88. LIGO/Virgo/KAGRA S250328ae: Subaru/PFS Spectroscopic Follow up and Candidates
  89. EP250421a: Nickel optical upper limit
  90. EP250416a / GRB 250416C: Gemini GMOS-S likely host galaxy redshift z = 0.963
  91. EP250421a: Upper limits from Fermi-GBM Observations
  92. SVOM/sb25042207: XRT observations
  93. SVOM/sb25042207: BOOTES-2 early optical upper limit
  94. SVOM/sb25042207: GOTO optical upper limits
  95. GRB 250421A: AstroSat CZTI detection
  96. SVOM/sb25042207: SVOM detection of an X-ray transient
  97. GRB250419A: VLA radio detection
  98. IceCube-250421A: DDOTI Detection of the LAST Candidate
  99. GRB 250419A: Mephisto Multi-band Optical Detection
  100. GRB 250419A: Calapai Observatory, Massa S. Giorgio (Messina), optical observations.

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