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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"

21813 results found.

  1. Fermi trigger No 780609036: Global MASTER-Net observations report
  2. IceCube Alert 250926.52: Global MASTER-Net observations report
  3. GRB 250920C: ULL-ASTRO-MASTER early detection of the optical afterglow with LCO 40-cm telescope at Siding Spring Observatory
  4. GRB 250925A: Swift/UVOT Upper Limits
  5. GRB 250925A: Mondy and AbAO optical observations
  6. GRB 250925A: COLIBRÍ photometric redshift
  7. GRB 250926A: DDOTI Optical Observations and Spatial Coincidence with the Orion Nebula
  8. GRB 250925A: JinShan optical observations
  9. GRB 250925A: 1.5m OSN optical detection and redshift with the 10.4m GTC/OSIRIS+
  10. GRB 250919A / EP250919a: Global MASTER Net before, during and after trigger optical observations
  11. GRB 250925A: COLIBRÍ optical photometry of the afterglow
  12. Fermi GRB 250926A: Global MASTER-Net observations report
  13. GRB 250925A: Optical Observations via Virtual Telescope Project, Italy
  14. GRB250925A: Liverpool Telescope optical observations
  15. GRB 250925A: NOT optical afterglow candidate
  16. GRB 250925A: Leavitt Observatory optical upper limit
  17. Swift GRB 250925A: Global MASTER-Net observations report
  18. GRB 250924A: 1.6m Mephisto optical upper limits
  19. GRB 250924A: SAO RAS optical observations
  20. GRB 250924A: NOT optical observations
  21. GRB 250924A: Swift/UVOT Detection
  22. GRB 250924A: J-band detection with WINTER
  23. GRB 250924A: GROWTH-India Telescope Upper Limits
  24. GRB 250924A: KAIT optical observations
  25. GRB 250924A: Mondy optical observations, afterglow fading
  26. GRB 250924A: Kilonova-Catcher optical afterglow detection
  27. GRB 250920C: Kilonova-Catcher optical afterglow detection
  28. GRB 250920C: TRT optical observation
  29. GRB 250924A: COLIBRÍ optical observations
  30. Swift GRB 250924A: Global MASTER-Net observations report
  31. GRB 250919A / EP250919a: further LCO optical observation
  32. GRB 250924A: DDOTI Detection of the Optical Counterpart
  33. GRB 250920C: KAIT optical observations
  34. GRB 250920C: VLT redshift confirmation z = 1.399
  35. EP250911a: e-MERLIN radio observations
  36. GRB 250920B: CrAO ZTSH optical observations
  37. GRB 250920C: SALT redshift confirmation
  38. GRB 250920C: COLIBRÍ optical observations
  39. Fermi GRB 250922B: Global MASTER-Net observations report
  40. GRB 250920B: SAO RAS optical observations
  41. GRB 250920C: NIR observations with WINTER
  42. GRB 250920B: NIR observations with WINTER
  43. Fermi trigger No 780156732: Global MASTER-Net observations report
  44. GRB 250920C: PRIME near-infrared detection
  45. GRB 250916A: Swift/UVOT Detection
  46. GRB 250916A: CrAO ZTSh R-band optical observations
  47. GRB 250916A: SAO RAS Zeiss-1000 optical observations
  48. GRB 250920B: Asiago optical observations
  49. GRB 250920B: Kitab-ISON optical upper limit
  50. GRB 250917B: Mondy and Zeiss-1000 SAO RAS optical observations, optical observations, afterglow candidate
  51. GRB 250920C: GTC/OSIRIS+ spectroscopic redshift z = 1.40
  52. GRB 250920C: GROWTH-India Telescope optical observations
  53. GRB 250916A: FTW optical and NIR observations of the counterpart
  54. GRB 250920C: Swift/UVOT Detection
  55. Swift GRB 250920C: Global MASTER-Net observations report
  56. GRB 250920B: Swift/UVOT Detection
  57. GRB 250920B: FTW optical and NIR observations of the counterpart
  58. GRB 250920C: Optical counterpart detection by LCO
  59. GRB 250920B: SVOM/C-GFT optical observations
  60. GRB 250920C: GOTO optical counterpart candidate
  61. GRB 250919A / EP250919a: LCO optical observation
  62. LIGO/Virgo/KAGRA S250920bq: Coverage and upper limits from MAXI/GSC observations
  63. Swift GRB 250920B: Global MASTER-Net observations report
  64. GRB 250919A / EP250919a: MASTER bright afterglow detection 24h after GRB time
  65. GRB 250916A: Mondy R-band optical observations
  66. Fermi GRB 250918A: Global MASTER-Net observations report
  67. GRB 250919A/EP250919A: Swift/UVOT afterglow detection
  68. GRB 250919A: Swift-XRT afterglow detection
  69. EP250919a/GRB 250919A: Gemini/GMOS-S spectroscopic redshift z = 1.145
  70. EP250919a: Global MASTER-Net observations report
  71. EP250919a: Einstein Probe detection of an X-ray transient
  72. Fermi GRB 250919A: Global MASTER-Net observations report
  73. GRB 250916A: KAIT optical observations
  74. GRB 250917B: VLT/HAWK-I near-infrared observations
  75. GRB 250916A: further SAO RAS optical observations
  76. GRB 250912A: SVOM/ECLAIRs refined analysis
  77. GRB 250917B: Swift/UVOT Upper Limits
  78. GRB 250916A: OSIRIS+/GTC redshift z = 2.015
  79. GRB 250916A: Swift-XRT observations
  80. EP250916a: EP-FXT follow-up observation
  81. GRB 250916A: MAO/AZT-22 optical observations
  82. GRB 250916A: SAO RAS optical observations
  83. GRB 250916A : GIT optical observations
  84. GRB250917B: WFST optical observations
  85. GRB 250916A: Swift ToO observations
  86. GRB 250917B: Swift-XRT observations
  87. Fermi GRB 250917B: Global MASTER-Net observations report
  88. GRB 250916A: GOTO optical counterpart candidate
  89. GRB 250910A: SVOM/ECLAIRs refined analysis
  90. EP250916a: Einstein Probe detection of an X-ray transient
  91. Fermi GRB 250916A: Global MASTER-Net observations report
  92. EP250827b: VLA Observations
  93. LIGO/Virgo/KAGRA S250818k: HCT optical follow-up
  94. SVOM/sb25091517: FRAM-ORM stellar flare - transient observation
  95. GRB 250912A: Swift/BAT-GUANO localization skymap of a possibly short burst
  96. GRB 250912A: SVOM/COLIBRÍ (FM-GFT) optical observations
  97. GRB 250912A: Swift-XRT observations
  98. GRB250912A: VLT/HAWK-I follow-up observations
  99. GRB 250912A: VLT observations
  100. GRB 250912A: SVOM/GRM analysis suggests a possible short GRB with extended emission

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