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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. EP251102a: OHP/T193 optical observations
  2. GRB 251103A: OHP/T193 optical observations
  3. GRB 251103A: Xinglong 2.16m optical detection
  4. GRB 251103A: Insight-HXMT detection
  5. GRB 251103A: KAIT optical observations
  6. GRB 251103B: Nanshan/HMT optical upper limit
  7. GRB 251013C: 7DT detection and Medium-band SED of Afterglow
  8. GRB 251103A: Swift/BAT-GUANO arcminute localization of a burst
  9. GRB 251103B: MITSuME Akeno optical upper limits
  10. GRB 251103B: Swift-XRT refined Analysis
  11. Fermi GRB 251103A: Global MASTER-Net observations report
  12. LIGO/Virgo/KAGRA S251103f: Identification of a GW compact binary merger candidate
  13. EP251102a: NIR observations with WINTER
  14. GRB 251103A: J-band detection with WINTER
  15. Swift GRB 251103B: Global MASTER-Net observations report
  16. GRB 251103B: GROWTH-India Telescope optical upper limits
  17. GRB 251103A: Kilonova-Catcher optical afterglow detection
  18. GRB 251103B: Enhanced Swift-XRT position
  19. GRB 251103B: Prompt enhanced Swift-XRT position
  20. GRB 251103B: Swift detection of a burst
  21. GRB 251103B: Fermi GBM Final Real-time Localization
  22. GRB 251103A: Swift/UVOT Detection
  23. GRB 251103A: Fermi GBM Observation
  24. GRB 251103A: SVOM/GRM observation
  25. GRB 251103A: Swift-XRT afterglow detection
  26. LIGO/Virgo/KAGRA S251031cq: Updated Sky localization
  27. GRB 251103A: SVOM/COLIBRÍ (FM-GFT) optical observations
  28. EP251102a: Einstein Probe detection of a fast X-ray transient
  29. GRB 251025B: OHP/T193 optical upper limit
  30. EP251102a (WXT 11900459650): LCO observations confirm COLIBRÍ candidate
  31. GRB 251103A: LCO optical observation
  32. EP251102.890: COLIBRÍ optical counterpart candidate
  33. GRB 251103A: GOTO optical afterglow detection
  34. GRB 251102A: AstroSat CZTI detection
  35. GRB 251026A: SVOM/COLIBRÍ (FM-GFT) confirmation of the optical counterpart
  36. GRB 251103A: NOT spectroscopic redshift z = 0.76
  37. GRB 251103A: BOOTES-2/TELMA optical afterglow
  38. GRB 251103A: LCO optical afterglow detection
  39. GRB 251103A: NOT optical afterglow candidate (duplicate submission)
  40. GRB 251103A: Fermi GBM Final Localization
  41. GRB 251103A: NOT optical afterglow candidate
  42. GRB 251103A: SVOM detection of a bright burst
  43. GRB 251102B: Fermi GBM Final Real-time Localization
  44. Fermi GRB 251102A: Global MASTER-Net observations report
  45. GRB 251102A: Fermi GBM Final Real-time Localization
  46. GRB 251031A: Fermi GBM Observation
  47. LIGO/Virgo/KAGRA S251031cq: Identification of a GW compact binary merger candidate
  48. GRB 251031A: Swift/BAT-GUANO localization skymap of a burst
  49. Konus-Wind detection of GRB 251028A
  50. GRB 251031A: BALROG localization (Fermi Trigger 783588065 / GRB 251031306)
  51. GRB 251031A: Fermi GBM Final Real-time Localization
  52. GRB 251025C: SVOM/GRM observation
  53. GRB 251028A: GECAM-B detection
  54. GRB 251028A: SVOM/GRM observation
  55. IceCube-251025A: Two Transient Candidates from the Zwicky Transient Facility
  56. GRB 251028A: Fermi GBM Observation
  57. GRB 251026B: SOAR Classification of GOTO25jgl/SN2025absf as a Type Ia supernova
  58. GRB 251022A: Swift-XRT confirmation of fading
  59. GRB 251026B: LBT near-infrared observations
  60. GRB 250926B: VZLUSAT-2 detection
  61. GRB 250926A: VZLUSAT-2 detection
  62. GRB 250925A: VZLUSAT-2 detection
  63. GRB 251026B: Fermi GBM Observation
  64. GRB 251026A/EP251026a: SVOM/VT optical counterpart
  65. GRB 251026A/EP251026a: EP-FXT follow-up observation
  66. The EP-WXT trigger 01709247588 is likely a flaring star
  67. GRB 251028B: Fermi/GBM observation
  68. GRB 251028B: Swift/BAT-GUANO localization skymap of a burst
  69. GRB 251028B: Glowbug gamma-ray detection
  70. GRB 251028A: Glowbug gamma-ray detection
  71. GRB 251028B: CALET Gamma-Ray Burst Monitor detection
  72. Fermi GRB 251028B: Global MASTER-Net observations report
  73. GRB 251025B: GROWTH-India Telescope continued multiband optical observations and rebrightening
  74. GRB 251028B: Fermi GBM Final Localization Correction
  75. GRB251026B: PRIME H-band upper limit
  76. GRB251025B: 3.6m DOT Optical Observations
  77. GRB 251028A: BALROG localization (Fermi Trigger 783314796 / GRB 251028143)
  78. GRB 251028A: MAXI/GSC detection
  79. GRB 251028A: Fermi GBM Final Real-time Localization
  80. The EP-WXT trigger 01709247525 is not a real source
  81. SVOM trigger sb25102702/GRB 251027A is not a GRB
  82. IceCube-251025A: Upper limits from a search for additional neutrino events in IceCube
  83. GRB 251025B: Swift-XRT confirmation of fading
  84. GRB 251013C : 3.4-m telescope of Iranian National Observatory (INO340) optical observations
  85. GRB 251026B: Swift-XRT observations of GOTO25jgl/AT2025absf
  86. GRB 251025C: Glowbug gamma-ray detection
  87. Fermi-LAT Gamma-ray Observations of IceCube-251025A
  88. GRB 251023B: Swift-UVOT Upper Limits
  89. Konus-Wind detection of GRB 251022A
  90. GRB 251027A: Swift-XRT observations
  91. EP251027.145: COLIBRÍ optical upper limits
  92. GRB 251022A: SVOM/GRM observation
  93. GRB 251026B: Swift ToO observations
  94. GRB 251026A/EP251026a: Einstein Probe detection of a fast X-ray transient
  95. GRB 251027A: LCO optical upper limit
  96. GRB 251027A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  97. GRB 251017A: Mondy AZT-33IK and Koshka Zeiss-1000 optical observations
  98. GRB 251023B / EP251023b: Mondy optical upper limit
  99. GRB 251017A: INASAN-Kislovodsk optical observations
  100. GRB 251026A: Mondy optical upper limit

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