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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. Fermi Gamma-ray Burst Monitor trigger 772720540/250627525 is not a GRB
  2. GRB 250625A: AbAO and INASAN Kislovodsk Optical Observations
  3. The EP-WXT trigger 01709179435 is likely a new outburst of the CV SS Cyg
  4. GRB 250625A: GTC/OSIRIS+ spectroscopic observations of the potential host galaxy
  5. GRB 250626A: Fermi GBM Final Real-time Localization
  6. Fermi Gamma-ray Burst Monitor trigger 772647532/250626680 is not a GRB
  7. GRB 250625A: Osservatorio Astronomico "Nastro Verde" optical observations: detection of an optical counterpart
  8. GRB 250625A: SVOM/C-GFT upper limit in early phase
  9. GRB 250625A: GECAM-B detection
  10. GRB 250625A: Swift/UVOT Upper Limits
  11. GRB 250625A: ABObservatory afterglow detection
  12. GRB 250625A: OHP/T193 optical detection
  13. GRB 250625A: COLIBRÍ optical observations
  14. GRB 250625A: Fermi-LAT detection
  15. GRB 250625A: Swift-XRT refined Analysis
  16. GRB 250625A: JinShan optical observations
  17. GRB250625A: Fermi GBM Observation
  18. Swift GRB 250625A: Global MASTER-Net observations report
  19. GRB 250625A: NOT z-band upper limit
  20. GRB 250625A: SVOM/VT optical confirmation
  21. GRB 250620B: Fermi GBM Observation
  22. GRB 250625A: SAO RAS possible optical afterglow
  23. GRB 250625A: Enhanced Swift-XRT position
  24. Fermi GRB 250625A: Global MASTER-Net observations report
  25. GRB 250625A: Swift detection of a burst
  26. GRB 250625A: Fermi GBM Final Real-time Localization
  27. GRB 250617B: Mondy and SAO RAS optical observations on 2025-06-23, 2025-06-24
  28. GRB 250620A: AstroSat CZTI detection
  29. The EP-WXT trigger 01709179396 is likely a flaring star CSTAR 38580
  30. GRB 241018A: Maidanak optical observations
  31. GRB 250620C: AstroSat CZTI detection
  32. Fermi GRB 250624A: Global MASTER-Net observations report
  33. GRB 250624A: Fermi GBM Final Real-time Localization
  34. sb25061207/GRB 250612D - SVOM/ECLAIRs refined analysis
  35. Fermi GRB 250623A: Global MASTER-Net observations report
  36. GRB 250623A: Fermi GBM Final Real-time Localization
  37. GRB 250521A: VZLUSAT-2 detection
  38. GRB 250617B: Swift-BAT refined analysis
  39. Fermi trigger No 772190032: Global MASTER-Net observations report
  40. Konus-Wind detection of GRB 250620C
  41. IPN triangulation of GRB 250620С (long/bright)
  42. GRB 250621B: SVOM/GRM detection of a possible magnetar X-ray burst
  43. GRB 250620C: SVOM/GRM observation
  44. GRB 250620A: SVOM/GRM observation of a short burst
  45. GRB250620A: Fermi GBM Observation
  46. GRB 250617B: Calapai Observatory, Massa S. Giorgio (Messina), optical observation.
  47. Fermi GRB 250621A: Global MASTER-Net observations report
  48. GRB 250619B: Fermi GBM Observation
  49. GRB 250621A: Fermi GBM Final Real-time Localization
  50. GRB 250620B: Swift/BAT-GUANO localization skymap of a burst
  51. GRB250620C: Fermi GBM Observation
  52. GRB 250506A - SVOM/ECLAIRs Refined analysis
  53. The EP-WXT trigger 01709179071 is likely a flaring star
  54. GRB 250620A: Swift/BAT-GUANO subthreshold detection of a possibly short burst
  55. GRB 250619B: Swift/BAT-GUANO localization skymap of a burst
  56. GRB 250620C: Fermi GBM Final Real-time Localization
  57. Fermi trigger No 772128434: Global MASTER-Net observations report
  58. GRB 250620B: Fermi GBM Final Real-time Localization
  59. GRB 250620A: Fermi GBM Final Real-time Localization
  60. EP-WXT trigger 01709179036: a new outburst of GRS 1739-278
  61. GRB 250617B: Nickel telescope optical observations
  62. GRB 250619B: Fermi GBM Final Real-time Localization
  63. Fermi trigger No 772058337: Global MASTER-Net observations report
  64. Fermi Gamma-ray Burst Monitor trigger 772058337/250619860 is not a GRB
  65. GRB 250615A: Kilonova-Catcher optical upper limits
  66. GRB 250619A: Fermi GBM Final Real-time Localization
  67. GRB 250617B: Assy AZT-20 Optical Observations
  68. GRB 250612A / Swift J1643.6−3854: Swift-BAT refined analysis
  69. Fermi GRB 250617A: Global MASTER-Net observations report
  70. GRB 250615A/EP250615a: FTW optical and NIR observations
  71. sb25061218/SVOM: OHP/T120 and OHP/T193 optical imaging and spectroscopic observations
  72. GRB 250617B: Swift/UVOT Detection
  73. GRB 250617B: Kilonova-Catcher optical afterglow detection
  74. GRB 250617B: VLT/X-shooter spectroscopic redshift z = 1.396
  75. GRB 250617B: COLIBRÍ optical observations
  76. GRB 250617B: NOT NIR observations of the afterglow
  77. GRB 250617B: Swift-XRT refined Analysis
  78. GRB 250617B: SVOM/VT optical observation
  79. GRB 250617B: NUTTelA-TAO early time optical observations
  80. Fermi trigger No 771886893: Global MASTER-Net observations report
  81. Swift GRB 250617B: Global MASTER-Net observations report
  82. GRB 250617B: GOTO optical upper limit
  83. GRB 250617B: Enhanced Swift-XRT position
  84. GRB 250617B: Fermi GBM Observation
  85. GRB 250615A: Swift-BAT refined analysis
  86. The EP-WXT trigger 01709178990 is likely a flaring star
  87. GRB 250617B: Fermi GBM Final Localization
  88. GRB 250617B: Ondrejov D50 optical afterglow detection
  89. GRB 250617B: SAO RAS optical observations
  90. GRB 250617B: Swift detection of a burst with an optical counterpart
  91. GRB 250615A: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
  92. GRB 250617A: Fermi GBM Final Real-time Localization
  93. IPN triangulation of GRB 250612C (short/hard)
  94. EP#01709178975: Swift-XRT counterpart detection
  95. EP-WXT trigger 01709178975: GOTO optical upper limit
  96. The EP-WXT trigger 01709178975 is likely a flaring star
  97. Konus-Wind detection of GRB 250615A / EP250615a
  98. GRB 250615A / EP250615a: AstroSat CZTI detection
  99. Fermi Gamma-ray Burst Monitor trigger 771803204/250616907 is not a GRB
  100. SVOM sb25061207: AbAO AS-32 Optical Upper Limit

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