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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. Swift GRB 250924A: Global MASTER-Net observations report
  2. GRB 250919A / EP250919a: further LCO optical observation
  3. GRB 250924A: DDOTI Detection of the Optical Counterpart
  4. GRB 250924A: Swift detection of a burst with an optical counterpart
  5. GRB 250920B: AbAO optical upper limits
  6. Konus-Wind detection of GRB 250920C
  7. GRB 250920C: KAIT optical observations
  8. GRB 250920C: VLT redshift confirmation z = 1.399
  9. EP250911a: e-MERLIN radio observations
  10. GRB 250920B: CrAO ZTSH optical observations
  11. GRB 250920C: SALT redshift confirmation
  12. GRB 250920C: COLIBRÍ optical observations
  13. GRB 250922C: AstroSat CZTI detection of a short burst
  14. Fermi GRB 250922B: Global MASTER-Net observations report
  15. GRB 250920B: SAO RAS optical observations
  16. GRB 250920C: NIR observations with WINTER
  17. GRB 250920B: NIR observations with WINTER
  18. Fermi trigger No 780156732: Global MASTER-Net observations report
  19. GRB 250922B: Fermi GBM Final Real-time Localization
  20. GRB 250920C: PRIME near-infrared detection
  21. Konus-Wind detection of GRB 250920B
  22. Konus-Wind detection of GRB 250920A
  23. IPN triangulation of GRB 250920A (long/bright)
  24. Konus-Wind detection of GRB 250911A
  25. GRB 250916A: Swift/UVOT Detection
  26. GRB 250920B: Glowbug gamma-ray detection
  27. GRB 250916A: CrAO ZTSh R-band optical observations
  28. GRB 250920C: Swift-XRT refined Analysis
  29. GRB 250916A: SAO RAS Zeiss-1000 optical observations
  30. GRB 250922A: Fermi GBM Final Localization
  31. GRB 250920B: Asiago optical observations
  32. GRB 250920B: Kitab-ISON optical upper limit
  33. GRB 250917B: Mondy and Zeiss-1000 SAO RAS optical observations, optical observations, afterglow candidate
  34. GRB 250920C: SVOM/GRM observation
  35. GRB 250920C: GTC/OSIRIS+ spectroscopic redshift z = 1.40
  36. GRB 250917B: KAIT optical upper limit
  37. GRB 250920A: NuSTAR detection of bright prompt emission
  38. GRB 250920C: GROWTH-India Telescope optical observations
  39. GRB 250920C: Swift-BAT refined analysis
  40. GRB 250920B: Swift-BAT refined analysis
  41. GRB 250920C: Enhanced Swift-XRT position
  42. GRB 250916A: FTW optical and NIR observations of the counterpart
  43. GRB 250920C: Swift/UVOT Detection
  44. GRB 250920B: Fermi GBM Observation
  45. GRB 250920A: Fermi GBM Detection
  46. GRB 250920C: Fermi GBM Observation
  47. Swift GRB 250920C: Global MASTER-Net observations report
  48. GRB 250920B: Swift/UVOT Detection
  49. GRB 250920B: FTW optical and NIR observations of the counterpart
  50. GRB 250920C: Optical counterpart detection by LCO
  51. GRB 250920A: SVOM/GRM observation
  52. GRB250920C: LCOGT Optical Detection
  53. GRB 250920B: Enhanced Swift-XRT position
  54. GRB 250920B: Swift-XRT refined Analysis
  55. GRB 250920B: SVOM/C-GFT optical observations
  56. GRB 250920C: GOTO optical counterpart candidate
  57. GRB 250919A / EP250919a: LCO optical observation
  58. Konus-Wind detection of GRB 250919A
  59. GRB 250920C: Swift detection of a burst
  60. GRB 250920C: Fermi GBM Final Real-time Localization
  61. LIGO/Virgo/KAGRA S250920bq: Coverage and upper limits from MAXI/GSC observations
  62. Swift GRB 250920B: Global MASTER-Net observations report
  63. GRB 250919A / EP250919a: Insight-HXMT detection
  64. GRB 250920A: AstroSat CZTI detection
  65. GRB 250920B: Swift detection of a burst with a bright optical counterpart.
  66. GRB 250920B: Fermi GBM Final Real-time Localization
  67. GRB 250920A: BALROG localization (Fermi Trigger 780029651 / GRB 250920121)
  68. GRB 250920A: Fermi GBM Final Localization
  69. GRB 250919A/EP250919a: SVOM/VT optical observation
  70. GRB 250919A / EP250919a: MASTER bright afterglow detection 24h after GRB time
  71. GRB 250916A: Mondy R-band optical observations
  72. GRB 250919A: Glowbug gamma-ray detection
  73. GRB 250919A: Fermi GBM Observation
  74. Fermi GRB 250918A: Global MASTER-Net observations report
  75. GRB 250919A / EP250919a: NuSTAR detection of bright prompt emission
  76. GRB 250918A: SVOM/GRM observation
  77. GRB 250919A/EP250919A: Swift/UVOT afterglow detection
  78. GRB 250919A: Swift-XRT afterglow detection
  79. GRB 250919A: Fermi-LAT detection
  80. EP250919a/GRB 250919A: Gemini/GMOS-S spectroscopic redshift z = 1.145
  81. GRB 250919A: SVOM/GRM observation of a very bright GRB
  82. GRB 250919A: BALROG localization (Fermi Trigger 779934537 / GRB 250919020)
  83. EP250919a: Global MASTER-Net observations report
  84. EP250919a: Einstein Probe detection of an X-ray transient
  85. Correction for GCN 41877: EP-WXT ID is 01709243841
  86. The EP-WXT trigger 01709243841: Las Cumbres discovery of the optical counterpart
  87. GRB 250916A: Fermi GBM Observation
  88. Fermi GRB 250919A: Global MASTER-Net observations report
  89. GRB 250919A: Fermi GBM Final Real-time Localization
  90. GRB 250916A: KAIT optical observations
  91. GRB 250917B: VLT/HAWK-I near-infrared observations
  92. GRB 250916A: NuSTAR detection of the prompt emission
  93. GRB 250916A: further SAO RAS optical observations
  94. GRB 250912A: SVOM/ECLAIRs refined analysis
  95. GRB 250917B: Swift-BAT refined analysis
  96. LIGO/Virgo/KAGRA S250918aw: 1 counterpart neutrino candidate event from an IceCube neutrino search
  97. GRB 250918A: BALROG localization (Fermi Trigger 779891543 / GRB 250918522)
  98. GRB 250918A: Fermi GBM Final Real-time Localization
  99. GRB 250917B: Swift/UVOT Upper Limits
  100. GRB 250916A: OSIRIS+/GTC redshift z = 2.015

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