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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 251026B: LBT near-infrared observations
  2. GRB 250926B: VZLUSAT-2 detection
  3. GRB 250926A: VZLUSAT-2 detection
  4. GRB 250925A: VZLUSAT-2 detection
  5. GRB 251026B: Fermi GBM Observation
  6. GRB 251026A/EP251026a: SVOM/VT optical counterpart
  7. GRB 251026A/EP251026a: EP-FXT follow-up observation
  8. The EP-WXT trigger 01709247588 is likely a flaring star
  9. GRB 251028B: Fermi/GBM observation
  10. GRB 251028B: Swift/BAT-GUANO localization skymap of a burst
  11. GRB 251028B: Glowbug gamma-ray detection
  12. GRB 251028A: Glowbug gamma-ray detection
  13. GRB 251028B: CALET Gamma-Ray Burst Monitor detection
  14. Fermi GRB 251028B: Global MASTER-Net observations report
  15. GRB 251025B: GROWTH-India Telescope continued multiband optical observations and rebrightening
  16. GRB 251028B: Fermi GBM Final Localization Correction
  17. GRB251026B: PRIME H-band upper limit
  18. GRB251025B: 3.6m DOT Optical Observations
  19. GRB 251028A: BALROG localization (Fermi Trigger 783314796 / GRB 251028143)
  20. GRB 251028A: MAXI/GSC detection
  21. GRB 251028A: Fermi GBM Final Real-time Localization
  22. The EP-WXT trigger 01709247525 is not a real source
  23. SVOM trigger sb25102702/GRB 251027A is not a GRB
  24. IceCube-251025A: Upper limits from a search for additional neutrino events in IceCube
  25. GRB 251025B: Swift-XRT confirmation of fading
  26. GRB 251013C : 3.4-m telescope of Iranian National Observatory (INO340) optical observations
  27. GRB 251026B: Swift-XRT observations of GOTO25jgl/AT2025absf
  28. GRB 251025C: Glowbug gamma-ray detection
  29. Fermi-LAT Gamma-ray Observations of IceCube-251025A
  30. GRB 251023B: Swift-UVOT Upper Limits
  31. Konus-Wind detection of GRB 251022A
  32. GRB 251027A: Swift-XRT observations
  33. EP251027.145: COLIBRÍ optical upper limits
  34. GRB 251022A: SVOM/GRM observation
  35. GRB 251026B: Swift ToO observations
  36. GRB 251026A/EP251026a: Einstein Probe detection of a fast X-ray transient
  37. GRB 251027A: LCO optical upper limit
  38. GRB 251027A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  39. GRB 251017A: Mondy AZT-33IK and Koshka Zeiss-1000 optical observations
  40. GRB 251023B / EP251023b: Mondy optical upper limit
  41. GRB 251017A: INASAN-Kislovodsk optical observations
  42. GRB 251026A: Mondy optical upper limit
  43. GRB 251025B: Mondy optical observations
  44. GRB 251025B: Kilonova-Catcher optical afterglow detection
  45. Konus-Wind detection of GRB 251016A (short/hard)
  46. GRB 251025B: VLT/MUSE spectroscopic redshift z = 2.003
  47. GRB 251027A: SVOM detection of a faint burst
  48. GRB 251026B: Tentative GOTO optical counterpart candidate
  49. GRB 251025C: AstroSat CZTI detection
  50. EP251023a: Mondy optical observations
  51. GRB 251025C: CALET Gamma-Ray Burst Monitor detection
  52. GRB 251025B: MAO/AZT-22 optical observations
  53. LIGO/Virgo/KAGRA S251026bn: Updated Sky localization
  54. Fermi GRB 251026B: Global MASTER-Net observations report
  55. Fermi GRB 251025C: Global MASTER-Net observations report
  56. LIGO/Virgo/KAGRA S251026bn: Identification of a GW compact binary merger candidate
  57. GRB 251026A: Swift-XRT observations
  58. GRB 251025B: OHP/T193 optical detection
  59. GRB 251025B: J-band detection with WINTER
  60. GRB 251026A: SVOM/C-GFT upper limit
  61. IceCube-251025A: DDOTI Optical Upper Limit
  62. GRB 251026A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  63. GRB 251026B: Fermi GBM Final Localization
  64. GRB 251026A: SVOM detection of a long burst
  65. GRB 251025B: SVOM/VT optical bump
  66. GRB 251025B: SVOM/COLIBRÍ (FM-GFT) strong rebrightening of the optical counterpart
  67. GRB 251023A: SVOM/GRM observation
  68. GRB 251025B: ULL-ASTRO-MASTER optical counterpart detection with IAC80 telescope at Teide Observatory
  69. GRB 251025C: Fermi GBM Final Real-time Localization
  70. Konus-Wind detection of GRB 251016B
  71. GRB 251025B: GROWTH-India Telescope optical observations
  72. GRB 251024A: Swift/UVOT Upper Limits
  73. GRB 251025B: Swift-XRT afterglow detection
  74. GRB 251024A: Swift-BAT refined analysis
  75. IceCube Alert 251025.57: Global MASTER-Net observations report
  76. GRB 251024A: Swift-XRT refined Analysis
  77. GRB 251025A (sb25102501): stellar flare confirmed
  78. GRB 251025B: SVOM/VT optical observations with VHF data
  79. GRB 251025B: MASTER OT detection
  80. GRB 251025B: SVOM/C-GFT optical counterpart detection
  81. GRB 251025B: SVOM detection of a burst
  82. IceCube-251025A - IceCube observation of a high-energy neutrino candidate track-like event
  83. GRB 251025A (sb25102501): Likely a stellar flare by SVOM/VT
  84. GRB 251025A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  85. GRB 251025A: SVOM/VT VHF optical upper limit
  86. GRB 251025A: SVOM detection of a faint burst
  87. GRB 251003A: VLA Detection
  88. GRB 251024A: Enhanced Swift-XRT position
  89. GRB 251023C: Glowbug gamma-ray detection
  90. GRB 251024A: LCOGT Optical Afterglow Detection
  91. GRB 251022A: KAIT optical observations
  92. GRB 251024A: Swift detection of a burst
  93. Swift GRB 251024A: Global MASTER-Net observations report
  94. GRB 251023B / EP251023b: COLIBRÍ Confirmation of the Fading Nature of the Optical Candidate
  95. GRB 251022A: COLIBRÍ Further Multi-frequency Optical Observations
  96. EP251023a: MAO/AZT-22 optical observations
  97. GRB 251023B: OHP/T193 optical observations
  98. EP251023a: OHP/T193 optical observations
  99. GRB 251023C: AstroSat CZTI detection
  100. EP251023b/GRB 251023B: JinShan optical observation

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