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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 250920C: GROWTH-India Telescope optical observations
  2. GRB 250920C: Swift-BAT refined analysis
  3. GRB 250920B: Swift-BAT refined analysis
  4. GRB 250920C: Enhanced Swift-XRT position
  5. GRB 250916A: FTW optical and NIR observations of the counterpart
  6. GRB 250920C: Swift/UVOT Detection
  7. GRB 250920B: Fermi GBM Observation
  8. GRB 250920A: Fermi GBM Detection
  9. GRB 250920C: Fermi GBM Observation
  10. Swift GRB 250920C: Global MASTER-Net observations report
  11. GRB 250920B: Swift/UVOT Detection
  12. GRB 250920B: FTW optical and NIR observations of the counterpart
  13. GRB 250920C: Optical counterpart detection by LCO
  14. GRB 250920A: SVOM/GRM observation
  15. GRB250920C: LCOGT Optical Detection
  16. GRB 250920B: Enhanced Swift-XRT position
  17. GRB 250920B: Swift-XRT refined Analysis
  18. GRB 250920B: SVOM/C-GFT optical observations
  19. GRB 250920C: GOTO optical counterpart candidate
  20. GRB 250919A / EP250919a: LCO optical observation
  21. Konus-Wind detection of GRB 250919A
  22. GRB 250920C: Swift detection of a burst
  23. GRB 250920C: Fermi GBM Final Real-time Localization
  24. LIGO/Virgo/KAGRA S250920bq: Coverage and upper limits from MAXI/GSC observations
  25. Swift GRB 250920B: Global MASTER-Net observations report
  26. GRB 250919A / EP250919a: Insight-HXMT detection
  27. GRB 250920A: AstroSat CZTI detection
  28. GRB 250920B: Swift detection of a burst with a bright optical counterpart.
  29. GRB 250920B: Fermi GBM Final Real-time Localization
  30. GRB 250920A: BALROG localization (Fermi Trigger 780029651 / GRB 250920121)
  31. GRB 250920A: Fermi GBM Final Localization
  32. GRB 250919A/EP250919a: SVOM/VT optical observation
  33. GRB 250919A / EP250919a: MASTER bright afterglow detection 24h after GRB time
  34. GRB 250916A: Mondy R-band optical observations
  35. GRB 250919A: Glowbug gamma-ray detection
  36. GRB 250919A: Fermi GBM Observation
  37. Fermi GRB 250918A: Global MASTER-Net observations report
  38. GRB 250919A / EP250919a: NuSTAR detection of bright prompt emission
  39. GRB 250918A: SVOM/GRM observation
  40. GRB 250919A/EP250919A: Swift/UVOT afterglow detection
  41. GRB 250919A: Swift-XRT afterglow detection
  42. GRB 250919A: Fermi-LAT detection
  43. EP250919a/GRB 250919A: Gemini/GMOS-S spectroscopic redshift z = 1.145
  44. GRB 250919A: SVOM/GRM observation of a very bright GRB
  45. GRB 250919A: BALROG localization (Fermi Trigger 779934537 / GRB 250919020)
  46. EP250919a: Global MASTER-Net observations report
  47. EP250919a: Einstein Probe detection of an X-ray transient
  48. Correction for GCN 41877: EP-WXT ID is 01709243841
  49. The EP-WXT trigger 01709243841: Las Cumbres discovery of the optical counterpart
  50. GRB 250916A: Fermi GBM Observation
  51. Fermi GRB 250919A: Global MASTER-Net observations report
  52. GRB 250919A: Fermi GBM Final Real-time Localization
  53. GRB 250916A: KAIT optical observations
  54. GRB 250917B: VLT/HAWK-I near-infrared observations
  55. GRB 250916A: NuSTAR detection of the prompt emission
  56. GRB 250916A: further SAO RAS optical observations
  57. GRB 250912A: SVOM/ECLAIRs refined analysis
  58. GRB 250917B: Swift-BAT refined analysis
  59. LIGO/Virgo/KAGRA S250918aw: 1 counterpart neutrino candidate event from an IceCube neutrino search
  60. GRB 250918A: BALROG localization (Fermi Trigger 779891543 / GRB 250918522)
  61. GRB 250918A: Fermi GBM Final Real-time Localization
  62. GRB 250917B: Swift/UVOT Upper Limits
  63. GRB 250916A: OSIRIS+/GTC redshift z = 2.015
  64. GRB 250916A: Swift-XRT observations
  65. EP250916a: EP-FXT follow-up observation
  66. GRB 250916A: MAO/AZT-22 optical observations
  67. GRB 250916A: SAO RAS optical observations
  68. GRB 250916A : GIT optical observations
  69. LIGO/Virgo/KAGRA S250917aq: Three counterpart neutrino candidates from IceCube neutrino searches
  70. LIGO/Virgo/KAGRA S250917aq: Updated Sky localization
  71. GRB 250916A: Glowbug gamma-ray detection
  72. GRB250917B: WFST optical observations
  73. GRB 250916A: Swift ToO observations
  74. GRB 250917B: Fermi GBM Observation
  75. GRB 250917B: Swift-XRT observations
  76. LIGO/Virgo/KAGRA S250917aq: Identification of a GW compact binary merger candidate
  77. Fermi GRB 250917B: Global MASTER-Net observations report
  78. GRB 250917B: Swift detection of a short burst
  79. GRB 250916A: GOTO optical counterpart candidate
  80. GRB 250917B: Fermi GBM Final Real-time Localization
  81. GRB 250917A: Fermi GBM Final Real-time Localization
  82. The EP-WXT trigger 01709241037 is likely a flaring star
  83. GRB 250916A: AstroSat CZTI detection of a bright long burst
  84. GRB 250910A: SVOM/ECLAIRs refined analysis
  85. EP250916a: Einstein Probe detection of an X-ray transient
  86. Fermi GRB 250916A: Global MASTER-Net observations report
  87. GRB 250916A: Fermi GBM Final Real-time Localization
  88. EP250827b: VLA Observations
  89. LIGO/Virgo/KAGRA S250818k: HCT optical follow-up
  90. SVOM/sb25091517: Confirmation of a stellar flare by SVOM/VT
  91. SVOM/sb25091517: FRAM-ORM stellar flare - transient observation
  92. SVOM/sb25091517: SVOM detection of an X-ray transient
  93. GRB 250912A: Swift/BAT-GUANO localization skymap of a possibly short burst
  94. GRB 250912A: SVOM/COLIBRÍ (FM-GFT) optical observations
  95. GRB 250912A: Swift-XRT observations
  96. GRB250912A: VLT/HAWK-I follow-up observations
  97. GRB 250912A: VLT observations
  98. GRB 250912A: Fermi GBM Observation
  99. GRB 250911A: Insight-HXMT detection
  100. GRB 250912A: SVOM/GRM analysis suggests a possible short GRB with extended emission

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