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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. LIGO/Virgo/KAGRA S250927ck: Updated Sky localization
  2. Fermi-LAT Gamma-ray Observations of IceCube-250926A
  3. GRB 250926A: triangulation location with Insight-HXMT/HE and Fermi/GBM
  4. GRB 250924A: SVOM/GRM observation
  5. GRB 250925A: Swift-XRT refined Analysis
  6. LIGO/Virgo/KAGRA S250927cy: Identification of a GW compact binary merger candidate
  7. LIGO/Virgo/KAGRA S250927ck: Identification of a GW compact binary merger candidate
  8. IceCube-250926A: Upper limits from a search for additional neutrino events in IceCube
  9. GRB 250926A: Insight-HXMT detection
  10. GRB 250926B: Fermi GBM Final Localization
  11. Fermi trigger No 780609036: Global MASTER-Net observations report
  12. IceCube Alert 250926.52: Global MASTER-Net observations report
  13. GRB 250920C: ULL-ASTRO-MASTER early detection of the optical afterglow with LCO 40-cm telescope at Siding Spring Observatory
  14. GRB 250926A: AstroSat CZTI detection
  15. GRB 250925A: Swift/UVOT Upper Limits
  16. GRB 250925A: Swift-BAT refined analysis
  17. GRB 250925A: Mondy and AbAO optical observations
  18. GRB 250925A: COLIBRÍ photometric redshift
  19. IceCube-250926A - IceCube observation of a high-energy neutrino candidate track-like event
  20. GRB 250925A: SVOM/GWAC-F60A upper limit
  21. GRB 250925A/EP250925a: EP-WXT detection
  22. GRB 250926A: DDOTI Optical Observations and Spatial Coincidence with the Orion Nebula
  23. GRB 250925A : MITSuME Akeno optical upper limits
  24. GRB 250925A: JinShan optical observations
  25. GRB 250925A: 1.5m OSN optical detection and redshift with the 10.4m GTC/OSIRIS+
  26. GRB 250919A / EP250919a: Global MASTER Net before, during and after trigger optical observations
  27. GRB 250925A: COLIBRÍ optical photometry of the afterglow
  28. Fermi GRB 250926A: Global MASTER-Net observations report
  29. GRB 250926A: Fermi GBM Final Real-time Localization
  30. GRB 250925A: Optical Observations via Virtual Telescope Project, Italy
  31. GRB250925A: Liverpool Telescope optical observations
  32. GRB 250925A: NOT optical afterglow candidate
  33. GRB 250925A: Leavitt Observatory optical upper limit
  34. GRB 250925A: Enhanced Swift-XRT position
  35. GRB 250924A: Swift-BAT refined analysis
  36. GRB 250925A: GROWTH-India Telescope Upper Limits
  37. GRB 250925A: Swift detection of a burst
  38. Swift GRB 250925A: Global MASTER-Net observations report
  39. GRB 250922A: SVOM/GRM observation
  40. GRB 250924A: 1.6m Mephisto optical upper limits
  41. GRB 250924A: SAO RAS optical observations
  42. GRB 250924A: NOT optical observations
  43. GRB 250924A: AstroSat CZTI detection
  44. GRB 250914A: AstroSat CZTI detection
  45. GRB 250920B: AstroSat CZTI detection
  46. GRB 250924A: SVOM/VT optical observation
  47. GRB 250924A: Swift/UVOT Detection
  48. GRB 250924A: Swift-XRT refined Analysis
  49. GRB 250924A: Enhanced Swift-XRT position
  50. GRB 250924A: J-band detection with WINTER
  51. GRB 250924A: GROWTH-India Telescope Upper Limits
  52. GRB 250924A: KAIT optical observations
  53. GRB 250924A: Mondy optical observations, afterglow fading
  54. GRB 250924A: Kilonova-Catcher optical afterglow detection
  55. GRB 250920C: Kilonova-Catcher optical afterglow detection
  56. GRB 250922B: SVOM/GRM observation
  57. GRB 250920C: TRT optical observation
  58. GRB 250924B: Fermi GBM Final Localization
  59. GRB 250924A: COLIBRÍ optical observations
  60. Swift GRB 250924A: Global MASTER-Net observations report
  61. GRB 250919A / EP250919a: further LCO optical observation
  62. GRB 250924A: DDOTI Detection of the Optical Counterpart
  63. GRB 250924A: Swift detection of a burst with an optical counterpart
  64. GRB 250920B: AbAO optical upper limits
  65. Konus-Wind detection of GRB 250920C
  66. GRB 250920C: KAIT optical observations
  67. GRB 250920C: VLT redshift confirmation z = 1.399
  68. EP250911a: e-MERLIN radio observations
  69. GRB 250920B: CrAO ZTSH optical observations
  70. GRB 250920C: SALT redshift confirmation
  71. GRB 250920C: COLIBRÍ optical observations
  72. GRB 250922C: AstroSat CZTI detection of a short burst
  73. Fermi GRB 250922B: Global MASTER-Net observations report
  74. GRB 250920B: SAO RAS optical observations
  75. GRB 250920C: NIR observations with WINTER
  76. GRB 250920B: NIR observations with WINTER
  77. Fermi trigger No 780156732: Global MASTER-Net observations report
  78. GRB 250922B: Fermi GBM Final Real-time Localization
  79. GRB 250920C: PRIME near-infrared detection
  80. Konus-Wind detection of GRB 250920B
  81. Konus-Wind detection of GRB 250920A
  82. IPN triangulation of GRB 250920A (long/bright)
  83. Konus-Wind detection of GRB 250911A
  84. GRB 250916A: Swift/UVOT Detection
  85. GRB 250920B: Glowbug gamma-ray detection
  86. GRB 250916A: CrAO ZTSh R-band optical observations
  87. GRB 250920C: Swift-XRT refined Analysis
  88. GRB 250916A: SAO RAS Zeiss-1000 optical observations
  89. GRB 250922A: Fermi GBM Final Localization
  90. GRB 250920B: Asiago optical observations
  91. GRB 250920B: Kitab-ISON optical upper limit
  92. GRB 250917B: Mondy and Zeiss-1000 SAO RAS optical observations, optical observations, afterglow candidate
  93. GRB 250920C: SVOM/GRM observation
  94. GRB 250920C: GTC/OSIRIS+ spectroscopic redshift z = 1.40
  95. GRB 250917B: KAIT optical upper limit
  96. GRB 250920A: NuSTAR detection of bright prompt emission
  97. GRB 250920C: GROWTH-India Telescope optical observations
  98. GRB 250920C: Swift-BAT refined analysis
  99. GRB 250920B: Swift-BAT refined analysis
  100. GRB 250920C: Enhanced Swift-XRT position

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