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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"

21793 results found.

  1. GRB 250924A: Swift/UVOT Detection
  2. GRB 250924A: J-band detection with WINTER
  3. GRB 250924A: GROWTH-India Telescope Upper Limits
  4. GRB 250924A: KAIT optical observations
  5. GRB 250924A: Mondy optical observations, afterglow fading
  6. GRB 250924A: Kilonova-Catcher optical afterglow detection
  7. GRB 250920C: Kilonova-Catcher optical afterglow detection
  8. GRB 250920C: TRT optical observation
  9. GRB 250924A: COLIBRÍ optical observations
  10. Swift GRB 250924A: Global MASTER-Net observations report
  11. GRB 250919A / EP250919a: further LCO optical observation
  12. GRB 250924A: DDOTI Detection of the Optical Counterpart
  13. GRB 250920C: KAIT optical observations
  14. GRB 250920C: VLT redshift confirmation z = 1.399
  15. EP250911a: e-MERLIN radio observations
  16. GRB 250920B: CrAO ZTSH optical observations
  17. GRB 250920C: SALT redshift confirmation
  18. GRB 250920C: COLIBRÍ optical observations
  19. Fermi GRB 250922B: Global MASTER-Net observations report
  20. GRB 250920B: SAO RAS optical observations
  21. GRB 250920C: NIR observations with WINTER
  22. GRB 250920B: NIR observations with WINTER
  23. Fermi trigger No 780156732: Global MASTER-Net observations report
  24. GRB 250920C: PRIME near-infrared detection
  25. GRB 250916A: Swift/UVOT Detection
  26. GRB 250916A: CrAO ZTSh R-band optical observations
  27. GRB 250916A: SAO RAS Zeiss-1000 optical observations
  28. GRB 250920B: Asiago optical observations
  29. GRB 250920B: Kitab-ISON optical upper limit
  30. GRB 250917B: Mondy and Zeiss-1000 SAO RAS optical observations, optical observations, afterglow candidate
  31. GRB 250920C: GTC/OSIRIS+ spectroscopic redshift z = 1.40
  32. GRB 250920C: GROWTH-India Telescope optical observations
  33. GRB 250916A: FTW optical and NIR observations of the counterpart
  34. GRB 250920C: Swift/UVOT Detection
  35. Swift GRB 250920C: Global MASTER-Net observations report
  36. GRB 250920B: Swift/UVOT Detection
  37. GRB 250920B: FTW optical and NIR observations of the counterpart
  38. GRB 250920C: Optical counterpart detection by LCO
  39. GRB 250920B: SVOM/C-GFT optical observations
  40. GRB 250920C: GOTO optical counterpart candidate
  41. GRB 250919A / EP250919a: LCO optical observation
  42. LIGO/Virgo/KAGRA S250920bq: Coverage and upper limits from MAXI/GSC observations
  43. Swift GRB 250920B: Global MASTER-Net observations report
  44. GRB 250919A / EP250919a: MASTER bright afterglow detection 24h after GRB time
  45. GRB 250916A: Mondy R-band optical observations
  46. Fermi GRB 250918A: Global MASTER-Net observations report
  47. GRB 250919A/EP250919A: Swift/UVOT afterglow detection
  48. GRB 250919A: Swift-XRT afterglow detection
  49. EP250919a/GRB 250919A: Gemini/GMOS-S spectroscopic redshift z = 1.145
  50. EP250919a: Global MASTER-Net observations report
  51. EP250919a: Einstein Probe detection of an X-ray transient
  52. Fermi GRB 250919A: Global MASTER-Net observations report
  53. GRB 250916A: KAIT optical observations
  54. GRB 250917B: VLT/HAWK-I near-infrared observations
  55. GRB 250916A: further SAO RAS optical observations
  56. GRB 250912A: SVOM/ECLAIRs refined analysis
  57. GRB 250917B: Swift/UVOT Upper Limits
  58. GRB 250916A: OSIRIS+/GTC redshift z = 2.015
  59. GRB 250916A: Swift-XRT observations
  60. EP250916a: EP-FXT follow-up observation
  61. GRB 250916A: MAO/AZT-22 optical observations
  62. GRB 250916A: SAO RAS optical observations
  63. GRB 250916A : GIT optical observations
  64. GRB250917B: WFST optical observations
  65. GRB 250916A: Swift ToO observations
  66. GRB 250917B: Swift-XRT observations
  67. Fermi GRB 250917B: Global MASTER-Net observations report
  68. GRB 250916A: GOTO optical counterpart candidate
  69. GRB 250910A: SVOM/ECLAIRs refined analysis
  70. EP250916a: Einstein Probe detection of an X-ray transient
  71. Fermi GRB 250916A: Global MASTER-Net observations report
  72. EP250827b: VLA Observations
  73. LIGO/Virgo/KAGRA S250818k: HCT optical follow-up
  74. SVOM/sb25091517: FRAM-ORM stellar flare - transient observation
  75. GRB 250912A: Swift/BAT-GUANO localization skymap of a possibly short burst
  76. GRB 250912A: SVOM/COLIBRÍ (FM-GFT) optical observations
  77. GRB 250912A: Swift-XRT observations
  78. GRB250912A: VLT/HAWK-I follow-up observations
  79. GRB 250912A: VLT observations
  80. GRB 250912A: SVOM/GRM analysis suggests a possible short GRB with extended emission
  81. Fermi GRB 250912A: Global MASTER-Net observations report
  82. EP250911a: Global MASTER-Net observations report
  83. EP250908c: tentative VLT/FORS2 redshift z = 2.87
  84. EP250911a: Upper limit from Fermi-GBM Observations
  85. EP250911a: refined analysis of the EP-WXT and EP-FXT observations
  86. GRB 250911A: MASTER optical counterpart observations
  87. EP250911a: SAO RAS optical observations
  88. EP250911a: Swift-XRT observations
  89. EP250911a: Optical detection with Kinder observations
  90. GRB 250911A: Swift/UVOT Detection
  91. GRB 250910A / EP250910a: Swift-XRT afterglow detection
  92. GRB 250910A / EP250910a : VLT/HAWK-I NIR counterpart discovery
  93. EP250911a: COLIBRÍ optical observations
  94. Fermi GRB 250910B: Global MASTER-Net observations report
  95. EP250910a: Global MASTER-Net observations report
  96. GRB 250903A: SVOM/ECLAIRs refined analysis
  97. GRB 250911A: Swift-XRT observations
  98. GRB 250911A: COLIBRÍ optical counterpart candidate
  99. GRB 250910A / EP250910a: VLT/HAWK-I near-infrared observations
  100. GRB 250702B: Late time Chandra observations

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