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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"
  1. IceCube 250406.951: DDOTI Optical Observations
  2. GRB 250406A: AstroSat CZTI detection
  3. IceCube Alert 250406.95: Global MASTER-Net observations report
  4. Fermi trigger No 765663719: Global MASTER-Net observations report
  5. EP250404a: Multi-band Optical Observations from UCAS-70 and XL-C14
  6. Fermi GRB 250406A: Global MASTER-Net observations report
  7. GRB 250404A: Calapai Observatory, Massa S. Giorgio (Messina), optical observations.
  8. GRB 250406A: Fermi GBM Final Real-time Localization
  9. EP250404a / GRB 250404A: Montarrenti Observatory optical observations
  10. Fermi trigger No 765619921: Global MASTER-Net observations report
  11. Fermi Gamma-ray Burst Monitor trigger 765619921/250406342 is not a GRB
  12. GRB 250404A / EP250404a: RC500 INASAN-Kislovodsk optical upper limit
  13. GRB 250404A / EP250404a: SVOM/GWAC-F60 and F50 observations
  14. EP250404a / GRB 250404A: J band observations by SYSU 80cm telescope
  15. Konus-Wind detection of GRB 250404A / EP250404a
  16. GRB 250404A / EP250404a: Mondy optical observations
  17. EP250404a: refined analysis of the EP-WXT and EP-FXT observations
  18. GRB 250404A / EP250404a: GMG spectroscopic redshift at z ~ 2.627
  19. GRB 250404A / EP250404a: Leavitt Observatory optical counterpart detection
  20. GRB 250402A: Calapai Observatory, Massa S. Giorgio (Messina), optical observations.
  21. EP250402a: Optical upper limit with PD 1.3m observations
  22. GRB 250404A / EP250404a: NOT optical observations
  23. GRB 250331D: Swift-XRT afterglow detection
  24. GRB 250404B: AstroSat CZTI detection of a short burst
  25. GRB 250403A: AstroSat CZTI detection
  26. EP250404a: Osservatorio Astronomico "Nastro Verde" optical observations: detection of an optical counterpart
  27. EP250404a: REM optical/NIR observations
  28. EP250404a: Seimei/TriCCS optical counterpart detection
  29. EP250404A: COLIBRÍ/DDRAGO Optical Observations
  30. EP250404A / GRB250404A: Ondrejov D50 optical afterglow detection
  31. EP250404a: LCO optical counterpart detection
  32. Fermi GRB 250404A: Global MASTER-Net observations report
  33. EP250404a: Xinglong decaying optical counterpart
  34. GRB 250403A: Montarrenti Observatory optical detection
  35. GRB 250404A: Fermi GBM Detection
  36. EP250404a: Global MASTER-Net observations report
  37. GRB 250403A: KAIT optical observations
  38. EP250404a: AKO Optical Afterglow Detection
  39. EP250404a: LAST detection of optical counterpart
  40. GRB 250402A: Swift/BAT-GUANO localization skymap of a burst
  41. EP250404a: Xinglong-2.16m spectroscopic redshift
  42. GRB 250403A: Fermi GBM observations
  43. GRB 250327B: VIRT Optical Upper Limit
  44. EP250404a: Mephisto multi-band optical detection
  45. GRB 250331C Swift-BAT refined analysis
  46. GRB 250331B Swift-BAT refined analysis
  47. GRB 250330A Swift-BAT refined analysis
  48. EP250321A: J band upper limit by SYSU 80cm telescope
  49. EP250404a: BOOTES-4/JGT optical afterglow detection
  50. EP250404a: Nanshan/HMT optical counterpart detection
  51. EP250404a: Einstein Probe detection of an X-ray transient
  52. GRB 250404A: Fermi GBM Final Real-time Localization
  53. GRB 250402A: Mondy optical observations
  54. GRB 250403A: Swift/UVOT Detection
  55. GRB 250402A: Swift/UVOT Upper Limits
  56. EP250402a: Optical upper limit with Kinder observations
  57. GRB 250403A: SVOM/VT optical observation
  58. GRB 250403A: REM NIR afterglow detection
  59. GRB 250403A: LCO optical counterpart detection
  60. IceCube-250330A: MASTER detection of PKS 2032+107 blazar flare with Zhirkov effect
  61. GRB 250403A: JinShan optical observations
  62. GRB 250402A: EP-FXT afterglow detection
  63. GRB 250403A: Optical counterpart detection by LCO.
  64. EP250402a: EP-FXT follow-up observations
  65. GRB 250403A: Swift-XRT observations
  66. GRB 250322A: 10 GHz VLA radio upper limits
  67. Fermi GRB 250403A: Global MASTER-Net observations report
  68. GRB 250403A: GOTO optical counterpart follow-up observations
  69. GRB 250402A: NUTTelA-TAO Early Optical Limits
  70. GRB 250403A: GMG Optical Observation
  71. GRB 250403A: 1.6m Mephisto multi-band optical detection
  72. GRB 250402A: Fermi GBM Observation
  73. GRB 250403A: SVOM/C-GFT optical observations
  74. GRB 250403A: GOTO detection of the optical afterglow
  75. GRB 250402A: Swift-XRT observations
  76. GRB 250403A : SVOM detection of a burst
  77. GRB 250403A: Fermi GBM Final Real-time Localization
  78. GRB 250225B: VLT host galaxy redshift z = 0.950
  79. GRB250402A: SVOM/COLIBRÍ (FM-GFT) Detection of the Optical Counterpart
  80. GRB 250402A: VLT/FORS2 spectroscopic redshift z = 2.823
  81. GRB 250402A: REM optical/NIR upper limits
  82. GRB 250402A: LCO optical counterpart detection
  83. GRB 250402A: refined SVOM/MXT data analysis
  84. The EP-WXT trigger 01709133862 is a flaring star
  85. EP250402a: Einstein Probe detection of a fast X-ray transient
  86. GRB 250402B: AstroSat CZTI detection of a short burst
  87. GRB 250402A: SVOM/VT optical counterpart
  88. GRB 250402A: SVOM detection of a burst
  89. GRB 250331C: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
  90. GRB 250314A: ALMA detection
  91. GRB 250329B: Swift/UVOT Upper Limit
  92. GRB 250329A: Swift/UVOT Upper Limit
  93. GRB 250327B: Swift/UVOT Detection
  94. GRB 250327A: Swift/UVOT Upper Limits
  95. GRB 250331E: SVOM/GRM observation
  96. GRB 250327B: Kilonova-Catcher Observations
  97. GRB250331D: AbAO optical observations
  98. GRB 250331D: Fermi GBM observation
  99. GRB 250331C: Swift/UVOT Upper Limits
  100. GRB 250331B: Swift/UVOT Upper Limits

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