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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"

37562 results found.

  1. GRB 250625A: VLT/X-shooter spectroscopic observations at the afterglow position
  2. GRB 250628A: VLT/X-shooter upper limits
  3. GRB 250628A: Swift/UVOT Upper Limits
  4. GRB 250628A: Swift-XRT refined Analysis
  5. Fermi GRB 250626A: Global MASTER-Net observations report
  6. Swift GRB 250628A: Global MASTER-Net observations report
  7. GRB 250628A: Enhanced Swift-XRT position
  8. GRB 250628A: Swift detection of a burst
  9. GRB 250625A: Swift-BAT refined analysis
  10. GRB 250625A: Leavitt Observatory afterglow detection
  11. Fermi Gamma-ray Burst Monitor trigger 772732642/250627665 is not a GRB
  12. Fermi Gamma-ray Burst Monitor trigger 772720540/250627525 is not a GRB
  13. GRB 250625A: AbAO and INASAN Kislovodsk Optical Observations
  14. GRB 250625A: GTC/OSIRIS+ spectroscopic observations of the potential host galaxy
  15. GRB 250626A: Fermi GBM Final Real-time Localization
  16. Fermi Gamma-ray Burst Monitor trigger 772647532/250626680 is not a GRB
  17. GRB 250625A: Osservatorio Astronomico "Nastro Verde" optical observations: detection of an optical counterpart
  18. GRB 250625A: SVOM/C-GFT upper limit in early phase
  19. GRB 250625A: GECAM-B detection
  20. GRB 250625A: Swift/UVOT Upper Limits
  21. GRB 250625A: ABObservatory afterglow detection
  22. GRB 250625A: OHP/T193 optical detection
  23. GRB 250625A: COLIBRÍ optical observations
  24. GRB 250625A: Fermi-LAT detection
  25. GRB 250625A: Swift-XRT refined Analysis
  26. GRB 250625A: JinShan optical observations
  27. GRB250625A: Fermi GBM Observation
  28. Swift GRB 250625A: Global MASTER-Net observations report
  29. GRB 250625A: NOT z-band upper limit
  30. GRB 250625A: SVOM/VT optical confirmation
  31. GRB 250620B: Fermi GBM Observation
  32. GRB 250625A: SAO RAS possible optical afterglow
  33. GRB 250625A: Enhanced Swift-XRT position
  34. Fermi GRB 250625A: Global MASTER-Net observations report
  35. GRB 250625A: Swift detection of a burst
  36. GRB 250625A: Fermi GBM Final Real-time Localization
  37. GRB 250617B: Mondy and SAO RAS optical observations on 2025-06-23, 2025-06-24
  38. GRB 250620A: AstroSat CZTI detection
  39. GRB 241018A: Maidanak optical observations
  40. GRB 250620C: AstroSat CZTI detection
  41. Fermi GRB 250624A: Global MASTER-Net observations report
  42. GRB 250624A: Fermi GBM Final Real-time Localization
  43. sb25061207/GRB 250612D - SVOM/ECLAIRs refined analysis
  44. Fermi GRB 250623A: Global MASTER-Net observations report
  45. GRB 250623A: Fermi GBM Final Real-time Localization
  46. GRB 250521A: VZLUSAT-2 detection
  47. GRB 250617B: Swift-BAT refined analysis
  48. Fermi trigger No 772190032: Global MASTER-Net observations report
  49. Konus-Wind detection of GRB 250620C
  50. IPN triangulation of GRB 250620C (long/bright)
  51. GRB 250621B: SVOM/GRM detection of a possible magnetar X-ray burst
  52. GRB 250620C: SVOM/GRM observation
  53. GRB 250620A: SVOM/GRM observation of a short burst
  54. GRB250620A: Fermi GBM Observation
  55. GRB 250617B: Calapai Observatory, Massa S. Giorgio (Messina), optical observation.
  56. Fermi GRB 250621A: Global MASTER-Net observations report
  57. GRB 250619B: Fermi GBM Observation
  58. GRB 250621A: Fermi GBM Final Real-time Localization
  59. GRB 250620B: Swift/BAT-GUANO localization skymap of a burst
  60. GRB250620C: Fermi GBM Observation
  61. GRB 250506A - SVOM/ECLAIRs Refined analysis
  62. GRB 250620A: Swift/BAT-GUANO subthreshold detection of a possibly short burst
  63. GRB 250619B: Swift/BAT-GUANO localization skymap of a burst
  64. GRB 250620C: Fermi GBM Final Real-time Localization
  65. Fermi trigger No 772128434: Global MASTER-Net observations report
  66. GRB 250620B: Fermi GBM Final Real-time Localization
  67. GRB 250620A: Fermi GBM Final Real-time Localization
  68. GRB 250617B: Nickel telescope optical observations
  69. GRB 250619B: Fermi GBM Final Real-time Localization
  70. Fermi trigger No 772058337: Global MASTER-Net observations report
  71. Fermi Gamma-ray Burst Monitor trigger 772058337/250619860 is not a GRB
  72. GRB 250615A: Kilonova-Catcher optical upper limits
  73. GRB 250619A: Fermi GBM Final Real-time Localization
  74. GRB 250617B: Assy AZT-20 Optical Observations
  75. GRB 250612A / Swift J1643.6−3854: Swift-BAT refined analysis
  76. Fermi GRB 250617A: Global MASTER-Net observations report
  77. GRB 250615A/EP250615a: FTW optical and NIR observations
  78. sb25061218/SVOM: OHP/T120 and OHP/T193 optical imaging and spectroscopic observations
  79. GRB 250617B: Swift/UVOT Detection
  80. GRB 250617B: Kilonova-Catcher optical afterglow detection
  81. GRB 250617B: VLT/X-shooter spectroscopic redshift z = 1.396
  82. GRB 250617B: COLIBRÍ optical observations
  83. GRB 250617B: NOT NIR observations of the afterglow
  84. GRB 250617B: Swift-XRT refined Analysis
  85. GRB 250617B: SVOM/VT optical observation
  86. GRB 250617B: NUTTelA-TAO early time optical observations
  87. Fermi trigger No 771886893: Global MASTER-Net observations report
  88. Swift GRB 250617B: Global MASTER-Net observations report
  89. GRB 250617B: GOTO optical upper limit
  90. GRB 250617B: Enhanced Swift-XRT position
  91. GRB 250617B: Fermi GBM Observation
  92. GRB 250615A: Swift-BAT refined analysis
  93. GRB 250617B: Fermi GBM Final Localization
  94. GRB 250617B: Ondrejov D50 optical afterglow detection
  95. GRB 250617B: SAO RAS optical observations
  96. GRB 250617B: Swift detection of a burst with an optical counterpart
  97. GRB 250615A: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
  98. GRB 250617A: Fermi GBM Final Real-time Localization
  99. IPN triangulation of GRB 250612C (short/hard)
  100. Konus-Wind detection of GRB 250615A / EP250615a

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