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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"

20960 results found.

  1. GRB 250507A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  2. GRB 250506A: Mephisto optical upper limits
  3. GRB 250506A: Swift ToO observations
  4. GRB 250502A: Bassano Bresciano Observatory upper limit
  5. IceCube Alert 250506.59: Global MASTER-Net observations report
  6. SVOM/sb25050601: EP-FXT observations
  7. GRB 250506A: REM optical/NIR upper limits
  8. GRB 250506A: Swift XRT observations and possible counterpart detection
  9. GRB 250506A: TRT optical observations
  10. GRB 250506A: SVOM/COLIBRÍ (FM-GFT) Upper Limits on the Optical Counterpart
  11. Fermi GRB 250505A: Global MASTER-Net observations report
  12. GRB 250504A: SVOM/VT upper limit
  13. GRB 250504A: REM optical/NIR observations
  14. GRB 250502A: REM optical/NIR observations
  15. GRB 250504A: MeerLICHT optical afterglow detection
  16. Fermi GRB 250504A: Global MASTER-Net observations report
  17. Swift GRB250504.98: Global MASTER-Net observations report
  18. GRB 250502A: Swift/UVOT Follow up
  19. GRB 250502A: Mondy and Tien-Shan Optical Observations
  20. GRB 250502A: KAIT optical observations
  21. GRB 250502A: Montarrenti Observatory optical detection
  22. GRB 250502A: Swift-XRT afterglow detection
  23. Fermi trigger No 767975731: Global MASTER-Net observations report
  24. GRB 250502A: NOT optical observations
  25. GRB 250502a: Liverpool Telescope optical follow-up
  26. GRB 250502A: LCO optical counterpart detection
  27. GRB 250502A: Swift ToO observations
  28. Fermi-LAT Gamma-ray Observations of IceCube-250429A
  29. GRB 250502B: DDOTI Optical Observations
  30. GRB 250502A: Early optical counterpart detection by LCO.
  31. GRB 250430A: Swift/UVOT Detection
  32. GRB 250502A: SVOM/VT optical bump
  33. GRB 250502A: TRT optical afterglow confirmation
  34. Fermi GRB 250502B: Global MASTER-Net observations report
  35. GRB 250430A: Optical Observations via Virtual Telescope Project, Italy
  36. GRB 250502A: SVOM/COLIBRÍ (FM-GFT) Detection of a Bright Optical Counterpart Candidate
  37. GRB 250430A: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
  38. GRB 250430A: SVOM/VT optical observations
  39. GRB 250430A: KAIT optical observations
  40. GRB 250430A / EP250430a: J-band upper limits with WINTER
  41. GRB 250430A: NUTTelA-TAO Early Measurements
  42. EP250427a / GRB 250427A: OHP/T193 photometric observations: third visit
  43. GRB 250430A: DDOTI Optical Observations
  44. GRB 250430A: Leavitt Observatory optical upper limit
  45. GRB 250430A: Bassano Bresciano Observatory upper limit
  46. SVOM/sb25043004: EP-FXT observations
  47. EP250430a/GRB 250430A: Einstein Probe WXT detection of the X-ray prompt emission
  48. EP 250427A: Optical counterpart detection by LCO.
  49. Swift GRB250430.73: Global MASTER-Net observations report
  50. EP250428b: FTW optical and NIR observations
  51. EP250427a/GRB250427A: HCT optical follow-up
  52. EP250427a / GRB 250427A: OHP/T193 continued photometric observations
  53. Fermi trigger No 767623859: Global MASTER-Net observations report
  54. EP250428b: SVOM/VT upper limit
  55. EP250428b: LAST optical upper limit
  56. EP250428b: Global MASTER-Net observations report
  57. Fermi-LAT Gamma-ray Observations of IceCube-250426A
  58. EP250427a / GRB 250427A: OHP/T193 photometric observations
  59. EP250427a: EP-FXT follow-up observations
  60. EP250427a/GRB 250427A: FTW optical and NIR observations of the counterpart
  61. EP250427a: Lesedi optical counterpart detection
  62. EP250427A: COLIBRÍ Continuing Optical Observations
  63. GRB250427A/EP250427a GIT optical afterglow detection:
  64. EP250427a: LT optical counterpart detection
  65. GRB 250427A: Swift-XRT refined Analysis
  66. EP250427a / GRB 250427A: LCO optical counterpart detection
  67. EP250427A/GRB250427A: Keck/LRIS redshift
  68. EP250427a: REM optical/NIR afterglow detection
  69. GRB 250424A: LCO optical observation
  70. EP250427A: COLIBRÍ Optical Detection
  71. EP250427a: TRT optical counterpart detection
  72. EP 250427a: BOOTES-7 optical afterglow candidate
  73. EP250427a: Global MASTER-Net observations report
  74. IceCube Alert 250426.74: Global MASTER-Net observations report
  75. GRB 250424A: PRIME near-infrared detection
  76. GRB 250424A: WINTER J-band detection
  77. GRB 250424A: EIRSAT-1 GMOD Detection
  78. GRB 250424A: SVOM/VT optical observation
  79. GRB 250419A: Mondy Optical Observations
  80. GRB 250424A: Swift/UVOT Detection
  81. Fermi-LAT gamma-ray observations of IceCube-250421A
  82. GRB 250424A: Skynet Optical Observations
  83. GRB 250424A: Kilonova-Catcher optical afterglow detection
  84. GRB 250419a: Continued Liverpool Telescope observations
  85. GRB 250419A: Liverpool Telescope optical upper limit
  86. GRB 250419A: SVOM/ECLAIRs refined analysis
  87. GRB 250424A: COLIBRÍ Detection of a Bright Optical Counterpart
  88. GRB 250424A: VLT/X-shooter spectroscopic redshift z = 0.310
  89. GRB 250424A: DDOTI Afterglow Detection
  90. GRB 250424A: REM optical/NIR afterglow detection
  91. Swift GRB 250424A: Global MASTER-Net observations report
  92. LIGO/Virgo/KAGRA S250328ae: Subaru/PFS Spectroscopic Follow up and Candidates
  93. EP250421a: Nickel optical upper limit
  94. EP250416a / GRB 250416C: Gemini GMOS-S likely host galaxy redshift z = 0.963
  95. EP250421a: Upper limits from Fermi-GBM Observations
  96. SVOM/sb25042207: XRT observations
  97. SVOM/sb25042207: BOOTES-2 early optical upper limit
  98. SVOM/sb25042207: GOTO optical upper limits
  99. SVOM/sb25042207: SVOM detection of an X-ray transient
  100. GRB250419A: VLA radio detection

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