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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"

39057 results found.

  1. GRB 250626A: Fermi GBM Final Real-time Localization
  2. Fermi Gamma-ray Burst Monitor trigger 772647532/250626680 is not a GRB
  3. GRB 250625A: Osservatorio Astronomico "Nastro Verde" optical observations: detection of an optical counterpart
  4. GRB 250625A: SVOM/C-GFT upper limit in early phase
  5. GRB 250625A: GECAM-B detection
  6. GRB 250625A: Swift/UVOT Upper Limits
  7. GRB 250625A: ABObservatory afterglow detection
  8. GRB 250625A: OHP/T193 optical detection
  9. GRB 250625A: COLIBRÍ optical observations
  10. GRB 250625A: Fermi-LAT detection
  11. GRB 250625A: Swift-XRT refined Analysis
  12. GRB 250625A: JinShan optical observations
  13. GRB250625A: Fermi GBM Observation
  14. Swift GRB 250625A: Global MASTER-Net observations report
  15. GRB 250625A: NOT z-band upper limit
  16. GRB 250625A: SVOM/VT optical confirmation
  17. GRB 250620B: Fermi GBM Observation
  18. GRB 250625A: SAO RAS possible optical afterglow
  19. GRB 250625A: Enhanced Swift-XRT position
  20. Fermi GRB 250625A: Global MASTER-Net observations report
  21. GRB 250625A: Swift detection of a burst
  22. GRB 250625A: Fermi GBM Final Real-time Localization
  23. GRB 250617B: Mondy and SAO RAS optical observations on 2025-06-23, 2025-06-24
  24. GRB 250620A: AstroSat CZTI detection
  25. GRB 241018A: Maidanak optical observations
  26. GRB 250620C: AstroSat CZTI detection
  27. Fermi GRB 250624A: Global MASTER-Net observations report
  28. GRB 250624A: Fermi GBM Final Real-time Localization
  29. sb25061207/GRB 250612D - SVOM/ECLAIRs refined analysis
  30. Fermi GRB 250623A: Global MASTER-Net observations report
  31. GRB 250623A: Fermi GBM Final Real-time Localization
  32. GRB 250521A: VZLUSAT-2 detection
  33. GRB 250617B: Swift-BAT refined analysis
  34. Fermi trigger No 772190032: Global MASTER-Net observations report
  35. Konus-Wind detection of GRB 250620C
  36. IPN triangulation of GRB 250620C (long/bright)
  37. GRB 250621B: SVOM/GRM detection of a possible magnetar X-ray burst
  38. GRB 250620C: SVOM/GRM observation
  39. GRB 250620A: SVOM/GRM observation of a short burst
  40. GRB250620A: Fermi GBM Observation
  41. GRB 250617B: Calapai Observatory, Massa S. Giorgio (Messina), optical observation.
  42. Fermi GRB 250621A: Global MASTER-Net observations report
  43. GRB 250619B: Fermi GBM Observation
  44. GRB 250621A: Fermi GBM Final Real-time Localization
  45. GRB 250620B: Swift/BAT-GUANO localization skymap of a burst
  46. GRB250620C: Fermi GBM Observation
  47. GRB 250506A - SVOM/ECLAIRs Refined analysis
  48. GRB 250620A: Swift/BAT-GUANO subthreshold detection of a possibly short burst
  49. GRB 250619B: Swift/BAT-GUANO localization skymap of a burst
  50. GRB 250620C: Fermi GBM Final Real-time Localization
  51. Fermi trigger No 772128434: Global MASTER-Net observations report
  52. GRB 250620B: Fermi GBM Final Real-time Localization
  53. GRB 250620A: Fermi GBM Final Real-time Localization
  54. GRB 250617B: Nickel telescope optical observations
  55. GRB 250619B: Fermi GBM Final Real-time Localization
  56. Fermi trigger No 772058337: Global MASTER-Net observations report
  57. Fermi Gamma-ray Burst Monitor trigger 772058337/250619860 is not a GRB
  58. GRB 250615A: Kilonova-Catcher optical upper limits
  59. GRB 250619A: Fermi GBM Final Real-time Localization
  60. GRB 250617B: Assy AZT-20 Optical Observations
  61. GRB 250612A / Swift J1643.6−3854: Swift-BAT refined analysis
  62. Fermi GRB 250617A: Global MASTER-Net observations report
  63. GRB 250615A/EP250615a: FTW optical and NIR observations
  64. sb25061218/SVOM: OHP/T120 and OHP/T193 optical imaging and spectroscopic observations
  65. GRB 250617B: Swift/UVOT Detection
  66. GRB 250617B: Kilonova-Catcher optical afterglow detection
  67. GRB 250617B: VLT/X-shooter spectroscopic redshift z = 1.396
  68. GRB 250617B: COLIBRÍ optical observations
  69. GRB 250617B: NOT NIR observations of the afterglow
  70. GRB 250617B: Swift-XRT refined Analysis
  71. GRB 250617B: SVOM/VT optical observation
  72. GRB 250617B: NUTTelA-TAO early time optical observations
  73. Fermi trigger No 771886893: Global MASTER-Net observations report
  74. Swift GRB 250617B: Global MASTER-Net observations report
  75. GRB 250617B: GOTO optical upper limit
  76. GRB 250617B: Enhanced Swift-XRT position
  77. GRB 250617B: Fermi GBM Observation
  78. GRB 250615A: Swift-BAT refined analysis
  79. GRB 250617B: Fermi GBM Final Localization
  80. GRB 250617B: Ondrejov D50 optical afterglow detection
  81. GRB 250617B: SAO RAS optical observations
  82. GRB 250617B: Swift detection of a burst with an optical counterpart
  83. GRB 250615A: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
  84. GRB 250617A: Fermi GBM Final Real-time Localization
  85. IPN triangulation of GRB 250612C (short/hard)
  86. Konus-Wind detection of GRB 250615A / EP250615a
  87. GRB 250615A / EP250615a: AstroSat CZTI detection
  88. Fermi Gamma-ray Burst Monitor trigger 771803204/250616907 is not a GRB
  89. SVOM sb25061207: AbAO AS-32 Optical Upper Limit
  90. GRB 250615A: COLIBRÍ optical upper limit
  91. GRB 250615A: DDOTI Optical Upper Limit
  92. GRB 250615A: Swift/UVOT Upper Limits
  93. Konus-Wind detection of GRB 250612C (short/hard with extended emission)
  94. GRB 250615A: Swift-XRT refined Analysis
  95. EP250615a/GRB 250615A: EP-WXT detection of a fast X-ray transient
  96. Fermi trigger No 771752663: Global MASTER-Net observations report
  97. GRB 250615A: Enhanced Swift-XRT position
  98. Fermi Gamma-ray Burst Monitor trigger 771718064/250615922 is not a GRB
  99. GRB 250615A: Prompt enhanced Swift-XRT position
  100. GRB 250615A: Swift detection of a burst

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