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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. Swift GRB 250702F: Global MASTER-Net observations report
  2. GRB 250702F: Fermi GBM Final Real-time Localization
  3. Fermi GBM Triggers 250702B, C, D and E are likely from the same source
  4. GRB 250702E: Fermi GBM Final Real-time Localization
  5. Konus-Wind detection of GRB 250627A
  6. IPN triangulation of GRB 250627A (short)
  7. GRB 250702A: Fermi GBM Detection
  8. GRB 250702D: Fermi GBM Final Localization Correction
  9. GRB 250702C: Fermi GBM Final Real-time Localization
  10. LIGO/Virgo/KAGRA S250702n: Identification of a GW compact binary merger candidate
  11. GRB 250702B: Fermi GBM Final Real-time Localization
  12. GRB 250702A: BALROG localization (Fermi Trigger 773142852 / GRB 250702413)
  13. GRB 250702A: Fermi GBM Final Real-time Localization
  14. LIGO/Virgo/KAGRA S250701bq: Identification of a GW compact binary merger candidate
  15. LIGO/Virgo/KAGRA S250701bp: Identification of a GW compact binary merger candidate
  16. Fermi Gamma-ray Burst Monitor trigger 772838080/250628885 is not a GRB
  17. GRB 250628B: Swift-XRT observations
  18. Fermi Gamma-ray Burst Monitor trigger 772981768/250630548 is not a GRB
  19. GRB 250628B: SVOM/VT optical upper limit
  20. GRB 250628B: EP-FXT counterpart detection
  21. LIGO/Virgo/KAGRA S250629bs: Updated Sky localization
  22. GRB 250627A: Insight-HXMT detection
  23. GRB 250627A: SVOM/GRM detection of a short burst
  24. LIGO/Virgo/KAGRA S250629ae: Updated Sky localization
  25. LIGO/Virgo/KAGRA S250629bs: Identification of a GW compact binary merger candidate
  26. LIGO/Virgo/KAGRA S250628am: Identification of a GW compact binary merger candidate (duplicate submission)
  27. LIGO/Virgo/KAGRA S250629ae: Identification of a GW compact binary merger candidate
  28. LIGO/Virgo/KAGRA S250628am: Updated Sky localization
  29. GRB 250628A: REM optical/NIR upper limits
  30. GRB 250628C: Fermi GBM Final Real-time Localization
  31. LIGO/Virgo/KAGRA S250628am: Identification of a GW compact binary merger candidate
  32. GRB 250628B: SVOM detection of a long burst
  33. Fermi Gamma-ray Burst Monitor trigger 772811638/250628579 is not a GRB
  34. GRB 250625A: VLT/X-shooter spectroscopic observations at the afterglow position
  35. GRB 250628A: VLT/X-shooter upper limits
  36. GRB 250628A: Swift/UVOT Upper Limits
  37. GRB 250628A: Swift-XRT refined Analysis
  38. Fermi GRB 250626A: Global MASTER-Net observations report
  39. Swift GRB 250628A: Global MASTER-Net observations report
  40. GRB 250628A: Enhanced Swift-XRT position
  41. GRB 250628A: Swift detection of a burst
  42. GRB 250625A: Swift-BAT refined analysis
  43. GRB 250625A: Leavitt Observatory afterglow detection
  44. Fermi Gamma-ray Burst Monitor trigger 772732642/250627665 is not a GRB
  45. Fermi Gamma-ray Burst Monitor trigger 772720540/250627525 is not a GRB
  46. GRB 250625A: AbAO and INASAN Kislovodsk Optical Observations
  47. The EP-WXT trigger 01709179435 is likely a new outburst of the CV SS Cyg
  48. GRB 250625A: GTC/OSIRIS+ spectroscopic observations of the potential host galaxy
  49. GRB 250626A: Fermi GBM Final Real-time Localization
  50. Fermi Gamma-ray Burst Monitor trigger 772647532/250626680 is not a GRB
  51. GRB 250625A: Osservatorio Astronomico "Nastro Verde" optical observations: detection of an optical counterpart
  52. GRB 250625A: SVOM/C-GFT upper limit in early phase
  53. GRB 250625A: GECAM-B detection
  54. GRB 250625A: Swift/UVOT Upper Limits
  55. GRB 250625A: ABObservatory afterglow detection
  56. GRB 250625A: OHP/T193 optical detection
  57. GRB 250625A: COLIBRÍ optical observations
  58. GRB 250625A: Fermi-LAT detection
  59. GRB 250625A: Swift-XRT refined Analysis
  60. GRB 250625A: JinShan optical observations
  61. GRB250625A: Fermi GBM Observation
  62. Swift GRB 250625A: Global MASTER-Net observations report
  63. GRB 250625A: NOT z-band upper limit
  64. GRB 250625A: SVOM/VT optical confirmation
  65. GRB 250620B: Fermi GBM Observation
  66. GRB 250625A: SAO RAS possible optical afterglow
  67. GRB 250625A: Enhanced Swift-XRT position
  68. Fermi GRB 250625A: Global MASTER-Net observations report
  69. GRB 250625A: Swift detection of a burst
  70. GRB 250625A: Fermi GBM Final Real-time Localization
  71. GRB 250617B: Mondy and SAO RAS optical observations on 2025-06-23, 2025-06-24
  72. GRB 250620A: AstroSat CZTI detection
  73. The EP-WXT trigger 01709179396 is likely a flaring star CSTAR 38580
  74. GRB 241018A: Maidanak optical observations
  75. GRB 250620C: AstroSat CZTI detection
  76. Fermi GRB 250624A: Global MASTER-Net observations report
  77. GRB 250624A: Fermi GBM Final Real-time Localization
  78. sb25061207/GRB 250612D - SVOM/ECLAIRs refined analysis
  79. Fermi GRB 250623A: Global MASTER-Net observations report
  80. GRB 250623A: Fermi GBM Final Real-time Localization
  81. GRB 250521A: VZLUSAT-2 detection
  82. GRB 250617B: Swift-BAT refined analysis
  83. Fermi trigger No 772190032: Global MASTER-Net observations report
  84. Konus-Wind detection of GRB 250620C
  85. IPN triangulation of GRB 250620С (long/bright)
  86. GRB 250621B: SVOM/GRM detection of a possible magnetar X-ray burst
  87. GRB 250620C: SVOM/GRM observation
  88. GRB 250620A: SVOM/GRM observation of a short burst
  89. GRB250620A: Fermi GBM Observation
  90. GRB 250617B: Calapai Observatory, Massa S. Giorgio (Messina), optical observation.
  91. Fermi GRB 250621A: Global MASTER-Net observations report
  92. GRB 250619B: Fermi GBM Observation
  93. GRB 250621A: Fermi GBM Final Real-time Localization
  94. GRB 250620B: Swift/BAT-GUANO localization skymap of a burst
  95. GRB250620C: Fermi GBM Observation
  96. GRB 250506A - SVOM/ECLAIRs Refined analysis
  97. The EP-WXT trigger 01709179071 is likely a flaring star
  98. GRB 250620A: Swift/BAT-GUANO subthreshold detection of a possibly short burst
  99. GRB 250619B: Swift/BAT-GUANO localization skymap of a burst
  100. GRB 250620C: Fermi GBM Final Real-time Localization

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