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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"

20540 results found.

  1. GRB 251002A: VLT/X-shooter spectroscopic redshift z = 2.178
  2. GRB 251003A: LCOGT Optical Detection
  3. GRB 251003A: COLIBRÍ optical detection of the fading afterglow
  4. GRB 251003A: 1.5m OSN afterglow candidate
  5. Swift GRB251003A: Global MASTER-Net observations report
  6. Fermi/SVOM GRB 251002A : MASTER OT earlier detection in 2 polarization filters
  7. GRB 251002A: SAO RAS optical observations
  8. GRB 251002A: ULL-ASTRO-MASTER early detection of the optical afterglow with the LCO 40-cm telescope at Sutherland Observatory
  9. GRB 251002A: LCO optical observation
  10. Fermi GRB 251002A: Global MASTER-Net observations report
  11. GRB 251001B: Swift/UVOT Detection
  12. GRB 251001B: COLIBRÍ optical observations
  13. GRB 251001B: GTC/OSIRIS+ spectroscopic redshift z = 2.162
  14. GRB 251001B: NOT optical observations
  15. Swift GRB 251001B: Global MASTER-Net observations report
  16. GRB 251001B: Further GOTO observations of optical counterpart.
  17. GRB 251001B: LCOGT Optical Observations
  18. GRB 251001B: TRT optical afterglow detection and potential host galaxy
  19. GRB 251001B: GOTO optical counterpart detection
  20. GRB 250910A / EP250910a: VLT limits on the possible associated supernova
  21. LIGO/Virgo/KAGRA S250830bp: SOAR spectroscopy of two DESGW candidates
  22. LIGO/Virgo/KAGRA S250818k: further MeerKAT monitoring
  23. GRB 250910A / EP250910a: VLT/X-shooter host galaxy redshift z = 0.592
  24. GRB 250925A: MAO/AZT-22 optical observations
  25. Fermi GRB 250929A: Global MASTER-Net observations report
  26. GRB 250925A: Mondy I-band optical observations
  27. Fermi-LAT Gamma-ray Observations of IceCube-250926A
  28. Fermi trigger No 780609036: Global MASTER-Net observations report
  29. IceCube Alert 250926.52: Global MASTER-Net observations report
  30. GRB 250920C: ULL-ASTRO-MASTER early detection of the optical afterglow with LCO 40-cm telescope at Siding Spring Observatory
  31. GRB 250925A: Swift/UVOT Upper Limits
  32. GRB 250925A: Mondy and AbAO optical observations
  33. GRB 250925A: COLIBRÍ photometric redshift
  34. GRB 250926A: DDOTI Optical Observations and Spatial Coincidence with the Orion Nebula
  35. GRB 250925A: JinShan optical observations
  36. GRB 250925A: 1.5m OSN optical detection and redshift with the 10.4m GTC/OSIRIS+
  37. GRB 250919A / EP250919a: Global MASTER Net before, during and after trigger optical observations
  38. GRB 250925A: COLIBRÍ optical photometry of the afterglow
  39. Fermi GRB 250926A: Global MASTER-Net observations report
  40. GRB 250925A: Optical Observations via Virtual Telescope Project, Italy
  41. GRB250925A: Liverpool Telescope optical observations
  42. GRB 250925A: NOT optical afterglow candidate
  43. GRB 250925A: Leavitt Observatory optical upper limit
  44. Swift GRB 250925A: Global MASTER-Net observations report
  45. GRB 250924A: 1.6m Mephisto optical upper limits
  46. GRB 250924A: SAO RAS optical observations
  47. GRB 250924A: NOT optical observations
  48. GRB 250924A: Swift/UVOT Detection
  49. GRB 250924A: J-band detection with WINTER
  50. GRB 250924A: GROWTH-India Telescope Upper Limits
  51. GRB 250924A: KAIT optical observations
  52. GRB 250924A: Mondy optical observations, afterglow fading
  53. GRB 250924A: Kilonova-Catcher optical afterglow detection
  54. GRB 250920C: Kilonova-Catcher optical afterglow detection
  55. GRB 250920C: TRT optical observation
  56. GRB 250924A: COLIBRÍ optical observations
  57. Swift GRB 250924A: Global MASTER-Net observations report
  58. GRB 250919A / EP250919a: further LCO optical observation
  59. GRB 250924A: DDOTI Detection of the Optical Counterpart
  60. GRB 250920C: KAIT optical observations
  61. GRB 250920C: VLT redshift confirmation z = 1.399
  62. EP250911a: e-MERLIN radio observations
  63. GRB 250920B: CrAO ZTSH optical observations
  64. GRB 250920C: SALT redshift confirmation
  65. GRB 250920C: COLIBRÍ optical observations
  66. Fermi GRB 250922B: Global MASTER-Net observations report
  67. GRB 250920B: SAO RAS optical observations
  68. GRB 250920C: NIR observations with WINTER
  69. GRB 250920B: NIR observations with WINTER
  70. Fermi trigger No 780156732: Global MASTER-Net observations report
  71. GRB 250920C: PRIME near-infrared detection
  72. GRB 250916A: Swift/UVOT Detection
  73. GRB 250916A: CrAO ZTSh R-band optical observations
  74. GRB 250916A: SAO RAS Zeiss-1000 optical observations
  75. GRB 250920B: Asiago optical observations
  76. GRB 250920B: Kitab-ISON optical upper limit
  77. GRB 250917B: Mondy and Zeiss-1000 SAO RAS optical observations, optical observations, afterglow candidate
  78. GRB 250920C: GTC/OSIRIS+ spectroscopic redshift z = 1.40
  79. GRB 250920C: GROWTH-India Telescope optical observations
  80. GRB 250916A: FTW optical and NIR observations of the counterpart
  81. GRB 250920C: Swift/UVOT Detection
  82. Swift GRB 250920C: Global MASTER-Net observations report
  83. GRB 250920B: Swift/UVOT Detection
  84. GRB 250920B: FTW optical and NIR observations of the counterpart
  85. GRB 250920C: Optical counterpart detection by LCO
  86. GRB 250920B: SVOM/C-GFT optical observations
  87. GRB 250920C: GOTO optical counterpart candidate
  88. GRB 250919A / EP250919a: LCO optical observation
  89. LIGO/Virgo/KAGRA S250920bq: Coverage and upper limits from MAXI/GSC observations
  90. Swift GRB 250920B: Global MASTER-Net observations report
  91. GRB 250919A / EP250919a: MASTER bright afterglow detection 24h after GRB time
  92. GRB 250916A: Mondy R-band optical observations
  93. Fermi GRB 250918A: Global MASTER-Net observations report
  94. GRB 250919A/EP250919A: Swift/UVOT afterglow detection
  95. GRB 250919A: Swift-XRT afterglow detection
  96. EP250919a/GRB 250919A: Gemini/GMOS-S spectroscopic redshift z = 1.145
  97. EP250919a: Global MASTER-Net observations report
  98. EP250919a: Einstein Probe detection of an X-ray transient
  99. Fermi GRB 250919A: Global MASTER-Net observations report
  100. GRB 250916A: KAIT optical observations

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