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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"

20958 results found.

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

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