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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"

15714 results found.

  1. GRB 250702F: GROWTH-India Telescope optical observations
  2. EP250704a / GRB 250704B: VLT/FORS2 optical afterglow detection
  3. GRB 250704A: REM retraction of optical afterglow detection and updated limit
  4. EP250702a: WFST optical observations
  5. EP250704a: COLIBRÍ optical counterpart candidate
  6. GRB 250702F: optical photometry from Konkoly
  7. GRB 250704A: REM detection of the optical afterglow
  8. GRB 250702F: SVOM/VT optical observation
  9. GRBs 250702B,C,D,E / EP250702a: 2.2m CAHA optical upper limit
  10. GRB 250702F: Leavitt Observatory optical observations
  11. GRB 250702F: AKO Optical Afterglow Detection
  12. GRBs 250702B,C,D,E / EP250702a: SVOM/GRM observation
  13. GRB 250702F: Skynet Optical Observations
  14. GRB 250424A: VIRT Optical Upper Limit
  15. GRB 250702B,C,D,E/EP250702a: COLIBRÍ optical upper limit
  16. GRB 250702F: TRT Optical Observation
  17. GRB 250703A: DDOTI Optical Upper Limit
  18. GRB 250702F: REM optical afterglow detection
  19. GRB 250702F: DDOTI Optical Observation
  20. EP250702a/GRB 250702B,C,D,E: GOTO optical upper limits
  21. GRB 250702F: COLIBRÍ Observations of the Afterglow
  22. GRB 250702F: GTC/OSIRIS+ spectroscopic redshift z = 1.520
  23. GRB 250702F: NOT observations of the optical afterglow
  24. GRB 250702F: MASTER optical afterglow observation
  25. GRB 250702F: GOTO optical counterpart detection
  26. GRB 250702F: Ondrejov D50 optical afterglow detection
  27. GRB 250702F: Swift detection of a burst with an optical counterpart
  28. GRB 250628B: SVOM/VT optical upper limit
  29. GRB 250628A: REM optical/NIR upper limits
  30. GRB 250628B: SVOM detection of a long burst
  31. GRB 250625A: VLT/X-shooter spectroscopic observations at the afterglow position
  32. GRB 250628A: Swift/UVOT Upper Limits
  33. GRB 250625A: Leavitt Observatory afterglow detection
  34. GRB 250625A: AbAO and INASAN Kislovodsk Optical Observations
  35. GRB 250625A: GTC/OSIRIS+ spectroscopic observations of the potential host galaxy
  36. GRB 250625A: Osservatorio Astronomico "Nastro Verde" optical observations: detection of an optical counterpart
  37. GRB 250625A: SVOM/C-GFT upper limit in early phase
  38. GRB 250625A: Swift/UVOT Upper Limits
  39. GRB 250625A: ABObservatory afterglow detection
  40. GRB 250625A: OHP/T193 optical detection
  41. GRB 250625A: COLIBRÍ optical observations
  42. GRB 250625A: JinShan optical observations
  43. GRB 250625A: NOT z-band upper limit
  44. GRB 250625A: SVOM/VT optical confirmation
  45. GRB 250625A: SAO RAS possible optical afterglow
  46. GRB 250617B: Mondy and SAO RAS optical observations on 2025-06-23, 2025-06-24
  47. GRB 241018A: Maidanak optical observations
  48. GRB 250621B: SVOM/GRM detection of a possible magnetar X-ray burst
  49. GRB 250620C: SVOM/GRM observation
  50. GRB 250620A: SVOM/GRM observation of a short burst
  51. GRB 250617B: Calapai Observatory, Massa S. Giorgio (Messina), optical observation.
  52. GRB 250617B: Nickel telescope optical observations
  53. GRB 250615A: Kilonova-Catcher optical upper limits
  54. GRB 250617B: Assy AZT-20 Optical Observations
  55. GRB 250615A/EP250615a: FTW optical and NIR observations
  56. sb25061218/SVOM: OHP/T120 and OHP/T193 optical imaging and spectroscopic observations
  57. GRB 250617B: Kilonova-Catcher optical afterglow detection
  58. GRB 250617B: VLT/X-shooter spectroscopic redshift z = 1.396
  59. GRB 250617B: COLIBRÍ optical observations
  60. GRB 250617B: NOT NIR observations of the afterglow
  61. GRB 250617B: SVOM/VT optical observation
  62. GRB 250617B: NUTTelA-TAO early time optical observations
  63. GRB 250617B: GOTO optical upper limit
  64. GRB 250617B: Ondrejov D50 optical afterglow detection
  65. GRB 250617B: SAO RAS optical observations
  66. GRB 250617B: Swift detection of a burst with an optical counterpart
  67. GRB 250615A: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
  68. EP-WXT trigger 01709178975: GOTO optical upper limit
  69. SVOM sb25061207: AbAO AS-32 Optical Upper Limit
  70. GRB 250615A: COLIBRÍ optical upper limit
  71. GRB 250615A: DDOTI Optical Upper Limit
  72. GRB 250615A: Swift/UVOT Upper Limits
  73. sb25061207/SVOM: T120 OHP optical upper limit
  74. sb25061207: Mephisto optical upper limits
  75. EP250612a / GRB 250612B: NOT optical observations of the afterglow candidate
  76. sb25061218: SVOM/COLIBRÍ (FM-GFT) optical upper limits
  77. sb25061207: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  78. EP250612a: refined analysis of the EP-WXT and EP-FXT observations
  79. GRB 250610B: J band upper limit by SYSU 80cm infrared telescope
  80. EP250612a: SVOM/VT optical candidate
  81. EP250612a/GRB 250612B: JinShan optical upper limit
  82. EP 250612a: AST3-3 Yaoan Optical Observation
  83. sb25061207: SVOM/VT optical counterpart
  84. GRB 250610B: Liverpool Telescope continued monitoring
  85. GRB 250610B: MISTRAL/T193 and T120 OHP further observations
  86. GRB 250610B: Swift/UVOT Detection
  87. EP250610A: Swift/UVOT Upper limits
  88. GRB 250610B: SVOM/COLIBRÍ (FM-GFT) optical observations
  89. GRB 250610B: REM optical/NIR observations
  90. EP250610a: Liverpool Telescope optical upper limits
  91. GRB 250610B: SVOM/VT optical shallow decay
  92. GRB 250610B: additional Liverpool Telescope optical observations
  93. GRB 250610B: EP-FXT follow-up observation and afterglow counterpart
  94. GRB 250610B: Swift-XRT counterpart detection
  95. GRB 250610B: SVOM/VT optical counterpart
  96. GRB 250610B: LT detection of the optical counterpart
  97. GRB 250610B: OHP/T120 optical counterpart candidate
  98. GRB 250610B: GOTO optical upper limit
  99. EP250610a: refined analysis of the EP-WXT and EP-FXT observations
  100. EP250610a: SVOM/VT optical upper limit

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