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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"

20579 results found.

  1. Fermi GRB 250504A: Global MASTER-Net observations report
  2. Swift GRB250504.98: Global MASTER-Net observations report
  3. GRB 250502A: Swift/UVOT Follow up
  4. GRB 250502A: Mondy and Tien-Shan Optical Observations
  5. GRB 250502A: KAIT optical observations
  6. GRB 250502A: Montarrenti Observatory optical detection
  7. GRB 250502A: Swift-XRT afterglow detection
  8. Fermi trigger No 767975731: Global MASTER-Net observations report
  9. GRB 250502A: NOT optical observations
  10. GRB 250502a: Liverpool Telescope optical follow-up
  11. GRB 250502A: LCO optical counterpart detection
  12. GRB 250502A: Swift ToO observations
  13. Fermi-LAT Gamma-ray Observations of IceCube-250429A
  14. GRB 250502B: DDOTI Optical Observations
  15. GRB 250502A: Early optical counterpart detection by LCO.
  16. GRB 250430A: Swift/UVOT Detection
  17. GRB 250502A: SVOM/VT optical bump
  18. GRB 250502A: TRT optical afterglow confirmation
  19. Fermi GRB 250502B: Global MASTER-Net observations report
  20. GRB 250430A: Optical Observations via Virtual Telescope Project, Italy
  21. GRB 250502A: SVOM/COLIBRÍ (FM-GFT) Detection of a Bright Optical Counterpart Candidate
  22. GRB 250430A: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
  23. GRB 250430A: SVOM/VT optical observations
  24. GRB 250430A: KAIT optical observations
  25. EP250428b: Pan-STARRS follow-up, upper limit on the optical counterpart, and possible host galaxy.
  26. GRB 250430A / EP250430a: J-band upper limits with WINTER
  27. GRB 250430A: NUTTelA-TAO Early Measurements
  28. EP250427a / GRB 250427A: OHP/T193 photometric observations: third visit
  29. GRB 250430A: DDOTI Optical Observations
  30. GRB 250430A: Leavitt Observatory optical upper limit
  31. GRB 250430A: Bassano Bresciano Observatory upper limit
  32. GRB 250430A / EP250430a: VLT/X-shooter spectroscopic redshift z = 0.767
  33. SVOM/sb25043004: EP-FXT observations
  34. EP250430a/GRB 250430A: Einstein Probe WXT detection of the X-ray prompt emission
  35. EP 250427A: Optical counterpart detection by LCO.
  36. Swift GRB250430.73: Global MASTER-Net observations report
  37. EP250428b: FTW optical and NIR observations
  38. EP250427a/GRB250427A: HCT optical follow-up
  39. EP250427a / GRB 250427A: OHP/T193 continued photometric observations
  40. Fermi trigger No 767623859: Global MASTER-Net observations report
  41. EP250428b: SVOM/VT upper limit
  42. EP250428b: LAST optical upper limit
  43. EP250428b: Global MASTER-Net observations report
  44. Fermi-LAT Gamma-ray Observations of IceCube-250426A
  45. EP250427a / GRB 250427A: OHP/T193 photometric observations
  46. EP250427a: EP-FXT follow-up observations
  47. EP250427a/GRB 250427A: FTW optical and NIR observations of the counterpart
  48. EP250427a: Lesedi optical counterpart detection
  49. EP250427A: COLIBRÍ Continuing Optical Observations
  50. GRB250427A/EP250427a GIT optical afterglow detection:
  51. EP250427a: LT optical counterpart detection
  52. GRB 250427A: Swift-XRT refined Analysis
  53. EP250427a / GRB 250427A: LCO optical counterpart detection
  54. EP250427A/GRB250427A: Keck/LRIS redshift
  55. EP250427a: REM optical/NIR afterglow detection
  56. GRB 250424A: LCO optical observation
  57. GRB 250427A/ EP250427a: Fermi-GBM Sub-Threshold Detection
  58. EP250427A: COLIBRÍ Optical Detection
  59. EP250427a: TRT optical counterpart detection
  60. EP 250427a: BOOTES-7 optical afterglow candidate
  61. EP250427a: Global MASTER-Net observations report
  62. IceCube Alert 250426.74: Global MASTER-Net observations report
  63. GRB 250424A: PRIME near-infrared detection
  64. GRB 250424A: WINTER J-band detection
  65. GRB 250424A: EIRSAT-1 GMOD Detection
  66. GRB 250424A: SVOM/VT optical observation
  67. GRB 250419A: Mondy Optical Observations
  68. GRB 250424A: Swift/UVOT Detection
  69. Fermi-LAT gamma-ray observations of IceCube-250421A
  70. GRB 250424A: Skynet Optical Observations
  71. GRB 250424A: Kilonova-Catcher optical afterglow detection
  72. GRB 250419a: Continued Liverpool Telescope observations
  73. GRB 250419A: Liverpool Telescope optical upper limit
  74. GRB 250419A: SVOM/ECLAIRs refined analysis
  75. GRB 250424A: COLIBRÍ Detection of a Bright Optical Counterpart
  76. GRB 250424A: VLT/X-shooter spectroscopic redshift z = 0.310
  77. GRB 250424A: likely host galaxy
  78. GRB 250424A: DDOTI Afterglow Detection
  79. GRB 250424A: REM optical/NIR afterglow detection
  80. Swift GRB 250424A: Global MASTER-Net observations report
  81. LIGO/Virgo/KAGRA S250328ae: Subaru/PFS Spectroscopic Follow up and Candidates
  82. EP250421a: Nickel optical upper limit
  83. EP250416a / GRB 250416C: Gemini GMOS-S likely host galaxy redshift z = 0.963
  84. EP250421a: Upper limits from Fermi-GBM Observations
  85. SVOM/sb25042207: XRT observations
  86. SVOM/sb25042207: BOOTES-2 early optical upper limit
  87. SVOM/sb25042207: GOTO optical upper limits
  88. SVOM/sb25042207: SVOM detection of an X-ray transient
  89. GRB250419A: VLA radio detection
  90. IceCube-250421A: DDOTI Detection of the LAST Candidate
  91. GRB 250419A: Mephisto Multi-band Optical Detection
  92. GRB 250419A: Calapai Observatory, Massa S. Giorgio (Messina), optical observations.
  93. IC-250421A: LAST optical observations of the IceCube neutrino candidate
  94. EP250421a: NOT optical observations
  95. GRB 250419A: Optical Observations via Virtual Telescope Project
  96. EP250421a: REM optical upper limit
  97. EP250421a: Swift/XRT counterpart detection
  98. EP250421A: COLIBRÍ Optical Upper Limit
  99. GRB 250419A: Mondy Continued Optical Observations
  100. Fermi GRB 250421A: Global MASTER-Net observations report

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