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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 251103A: Kilonova-Catcher optical afterglow detection
  2. GRB 251103B: Enhanced Swift-XRT position
  3. GRB 251103B: Prompt enhanced Swift-XRT position
  4. GRB 251103B: Swift detection of a burst
  5. GRB 251103B: Fermi GBM Final Real-time Localization
  6. GRB 251103A: Swift/UVOT Detection
  7. GRB 251103A: Fermi GBM Observation
  8. GRB 251103A: SVOM/GRM observation
  9. GRB 251103A: Swift-XRT afterglow detection
  10. LIGO/Virgo/KAGRA S251031cq: Updated Sky localization
  11. GRB 251103A: SVOM/COLIBRÍ (FM-GFT) optical observations
  12. EP251102a: Einstein Probe detection of a fast X-ray transient
  13. GRB 251025B: OHP/T193 optical upper limit
  14. EP251102a (WXT 11900459650): LCO observations confirm COLIBRÍ candidate
  15. GRB 251103A: LCO optical observation
  16. EP251102.890: COLIBRÍ optical counterpart candidate
  17. GRB 251103A: GOTO optical afterglow detection
  18. GRB 251102A: AstroSat CZTI detection
  19. GRB 251026A: SVOM/COLIBRÍ (FM-GFT) confirmation of the optical counterpart
  20. GRB 251103A: NOT spectroscopic redshift z = 0.76
  21. GRB 251103A: BOOTES-2/TELMA optical afterglow
  22. GRB 251103A: LCO optical afterglow detection
  23. GRB 251103A: NOT optical afterglow candidate (duplicate submission)
  24. GRB 251103A: Fermi GBM Final Localization
  25. GRB 251103A: NOT optical afterglow candidate
  26. GRB 251103A: SVOM detection of a bright burst
  27. GRB 251102B: Fermi GBM Final Real-time Localization
  28. Fermi GRB 251102A: Global MASTER-Net observations report
  29. GRB 251102A: Fermi GBM Final Real-time Localization
  30. GRB 251031A: Fermi GBM Observation
  31. LIGO/Virgo/KAGRA S251031cq: Identification of a GW compact binary merger candidate
  32. GRB 251031A: Swift/BAT-GUANO localization skymap of a burst
  33. Konus-Wind detection of GRB 251028A
  34. GRB 251031A: BALROG localization (Fermi Trigger 783588065 / GRB 251031306)
  35. GRB 251031A: Fermi GBM Final Real-time Localization
  36. GRB 251025C: SVOM/GRM observation
  37. GRB 251028A: GECAM-B detection
  38. GRB 251028A: SVOM/GRM observation
  39. IceCube-251025A: Two Transient Candidates from the Zwicky Transient Facility
  40. GRB 251028A: Fermi GBM Observation
  41. GRB 251026B: SOAR Classification of GOTO25jgl/SN2025absf as a Type Ia supernova
  42. GRB 251022A: Swift-XRT confirmation of fading
  43. GRB 251026B: LBT near-infrared observations
  44. GRB 250926B: VZLUSAT-2 detection
  45. GRB 250926A: VZLUSAT-2 detection
  46. GRB 250925A: VZLUSAT-2 detection
  47. GRB 251026B: Fermi GBM Observation
  48. GRB 251026A/EP251026a: SVOM/VT optical counterpart
  49. GRB 251026A/EP251026a: EP-FXT follow-up observation
  50. The EP-WXT trigger 01709247588 is likely a flaring star
  51. GRB 251028B: Fermi/GBM observation
  52. GRB 251028B: Swift/BAT-GUANO localization skymap of a burst
  53. GRB 251028B: Glowbug gamma-ray detection
  54. GRB 251028A: Glowbug gamma-ray detection
  55. GRB 251028B: CALET Gamma-Ray Burst Monitor detection
  56. Fermi GRB 251028B: Global MASTER-Net observations report
  57. GRB 251025B: GROWTH-India Telescope continued multiband optical observations and rebrightening
  58. GRB 251028B: Fermi GBM Final Localization Correction
  59. GRB251026B: PRIME H-band upper limit
  60. GRB251025B: 3.6m DOT Optical Observations
  61. GRB 251028A: BALROG localization (Fermi Trigger 783314796 / GRB 251028143)
  62. GRB 251028A: MAXI/GSC detection
  63. GRB 251028A: Fermi GBM Final Real-time Localization
  64. The EP-WXT trigger 01709247525 is not a real source
  65. SVOM trigger sb25102702/GRB 251027A is not a GRB
  66. IceCube-251025A: Upper limits from a search for additional neutrino events in IceCube
  67. GRB 251025B: Swift-XRT confirmation of fading
  68. GRB 251013C : 3.4-m telescope of Iranian National Observatory (INO340) optical observations
  69. GRB 251026B: Swift-XRT observations of GOTO25jgl/AT2025absf
  70. GRB 251025C: Glowbug gamma-ray detection
  71. Fermi-LAT Gamma-ray Observations of IceCube-251025A
  72. GRB 251023B: Swift-UVOT Upper Limits
  73. Konus-Wind detection of GRB 251022A
  74. GRB 251027A: Swift-XRT observations
  75. EP251027.145: COLIBRÍ optical upper limits
  76. GRB 251022A: SVOM/GRM observation
  77. GRB 251026B: Swift ToO observations
  78. GRB 251026A/EP251026a: Einstein Probe detection of a fast X-ray transient
  79. GRB 251027A: LCO optical upper limit
  80. GRB 251027A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  81. GRB 251017A: Mondy AZT-33IK and Koshka Zeiss-1000 optical observations
  82. GRB 251023B / EP251023b: Mondy optical upper limit
  83. GRB 251017A: INASAN-Kislovodsk optical observations
  84. GRB 251026A: Mondy optical upper limit
  85. GRB 251025B: Mondy optical observations
  86. GRB 251025B: Kilonova-Catcher optical afterglow detection
  87. Konus-Wind detection of GRB 251016A (short/hard)
  88. GRB 251025B: VLT/MUSE spectroscopic redshift z = 2.003
  89. GRB 251027A: SVOM detection of a faint burst
  90. GRB 251026B: Tentative GOTO optical counterpart candidate
  91. GRB 251025C: AstroSat CZTI detection
  92. EP251023a: Mondy optical observations
  93. GRB 251025C: CALET Gamma-Ray Burst Monitor detection
  94. GRB 251025B: MAO/AZT-22 optical observations
  95. LIGO/Virgo/KAGRA S251026bn: Updated Sky localization
  96. Fermi GRB 251026B: Global MASTER-Net observations report
  97. Fermi GRB 251025C: Global MASTER-Net observations report
  98. LIGO/Virgo/KAGRA S251026bn: Identification of a GW compact binary merger candidate
  99. GRB 251026A: Swift-XRT observations
  100. GRB 251025B: OHP/T193 optical detection

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