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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. GRB 250702F: COLIBRÍ Observations of the Afterglow
  2. EP250702a : an X-ray transient detected by Einstein Probe likely associated with GRB 250702B,C,D,E
  3. Fermi GRB 250702E: Global MASTER-Net observations report
  4. Fermi GRB 250702B: Global MASTER-Net observations report
  5. GRB 250702D, C, E: Swift/BAT-GUANO localization skymap of a burst or galactic transient
  6. GRB 250702F: Enhanced Swift-XRT position
  7. GRB 250702F: GTC/OSIRIS+ spectroscopic redshift z = 1.520
  8. GRB 250702F: NOT observations of the optical afterglow
  9. GRB 250702F: MASTER optical afterglow observation
  10. Fermi GRB 250702F: Global MASTER-Net observations report
  11. Fermi GRB 250702C: Global MASTER-Net observations report
  12. GRB 250702F: GOTO optical counterpart detection
  13. GRB 250702F: Ondrejov D50 optical afterglow detection
  14. GRB 250702F: Swift detection of a burst with an optical counterpart
  15. Swift GRB 250702F: Global MASTER-Net observations report
  16. GRB 250702F: Fermi GBM Final Real-time Localization
  17. Fermi GBM Triggers 250702B, C, D and E are likely from the same source
  18. GRB 250702E: Fermi GBM Final Real-time Localization
  19. Konus-Wind detection of GRB 250627A
  20. IPN triangulation of GRB 250627A (short)
  21. GRB 250702A: Fermi GBM Detection
  22. GRB 250702D: Fermi GBM Final Localization Correction
  23. GRB 250702C: Fermi GBM Final Real-time Localization
  24. LIGO/Virgo/KAGRA S250702n: Identification of a GW compact binary merger candidate
  25. GRB 250702B: Fermi GBM Final Real-time Localization
  26. GRB 250702A: BALROG localization (Fermi Trigger 773142852 / GRB 250702413)
  27. GRB 250702A: Fermi GBM Final Real-time Localization
  28. LIGO/Virgo/KAGRA S250701bq: Identification of a GW compact binary merger candidate
  29. LIGO/Virgo/KAGRA S250701bp: Identification of a GW compact binary merger candidate
  30. Fermi Gamma-ray Burst Monitor trigger 772838080/250628885 is not a GRB
  31. GRB 250628B: Swift-XRT observations
  32. Fermi Gamma-ray Burst Monitor trigger 772981768/250630548 is not a GRB
  33. GRB 250628B: SVOM/VT optical upper limit
  34. GRB 250628B: EP-FXT counterpart detection
  35. LIGO/Virgo/KAGRA S250629bs: Updated Sky localization
  36. GRB 250627A: Insight-HXMT detection
  37. GRB 250627A: SVOM/GRM detection of a short burst
  38. LIGO/Virgo/KAGRA S250629ae: Updated Sky localization
  39. LIGO/Virgo/KAGRA S250629bs: Identification of a GW compact binary merger candidate
  40. LIGO/Virgo/KAGRA S250628am: Identification of a GW compact binary merger candidate (duplicate submission)
  41. LIGO/Virgo/KAGRA S250629ae: Identification of a GW compact binary merger candidate
  42. LIGO/Virgo/KAGRA S250628am: Updated Sky localization
  43. GRB 250628A: REM optical/NIR upper limits
  44. GRB 250628C: Fermi GBM Final Real-time Localization
  45. LIGO/Virgo/KAGRA S250628am: Identification of a GW compact binary merger candidate
  46. GRB 250628B: SVOM detection of a long burst
  47. Fermi Gamma-ray Burst Monitor trigger 772811638/250628579 is not a GRB
  48. GRB 250625A: VLT/X-shooter spectroscopic observations at the afterglow position
  49. GRB 250628A: VLT/X-shooter upper limits
  50. GRB 250628A: Swift/UVOT Upper Limits
  51. GRB 250628A: Swift-XRT refined Analysis
  52. Fermi GRB 250626A: Global MASTER-Net observations report
  53. Swift GRB 250628A: Global MASTER-Net observations report
  54. GRB 250628A: Enhanced Swift-XRT position
  55. GRB 250628A: Swift detection of a burst
  56. GRB 250625A: Swift-BAT refined analysis
  57. GRB 250625A: Leavitt Observatory afterglow detection
  58. Fermi Gamma-ray Burst Monitor trigger 772732642/250627665 is not a GRB
  59. Fermi Gamma-ray Burst Monitor trigger 772720540/250627525 is not a GRB
  60. GRB 250625A: AbAO and INASAN Kislovodsk Optical Observations
  61. The EP-WXT trigger 01709179435 is likely a new outburst of the CV SS Cyg
  62. GRB 250625A: GTC/OSIRIS+ spectroscopic observations of the potential host galaxy
  63. GRB 250626A: Fermi GBM Final Real-time Localization
  64. Fermi Gamma-ray Burst Monitor trigger 772647532/250626680 is not a GRB
  65. GRB 250625A: Osservatorio Astronomico "Nastro Verde" optical observations: detection of an optical counterpart
  66. GRB 250625A: SVOM/C-GFT upper limit in early phase
  67. GRB 250625A: GECAM-B detection
  68. GRB 250625A: Swift/UVOT Upper Limits
  69. GRB 250625A: ABObservatory afterglow detection
  70. GRB 250625A: OHP/T193 optical detection
  71. GRB 250625A: COLIBRÍ optical observations
  72. GRB 250625A: Fermi-LAT detection
  73. GRB 250625A: Swift-XRT refined Analysis
  74. GRB 250625A: JinShan optical observations
  75. GRB250625A: Fermi GBM Observation
  76. Swift GRB 250625A: Global MASTER-Net observations report
  77. GRB 250625A: NOT z-band upper limit
  78. GRB 250625A: SVOM/VT optical confirmation
  79. GRB 250620B: Fermi GBM Observation
  80. GRB 250625A: SAO RAS possible optical afterglow
  81. GRB 250625A: Enhanced Swift-XRT position
  82. Fermi GRB 250625A: Global MASTER-Net observations report
  83. GRB 250625A: Swift detection of a burst
  84. GRB 250625A: Fermi GBM Final Real-time Localization
  85. GRB 250617B: Mondy and SAO RAS optical observations on 2025-06-23, 2025-06-24
  86. GRB 250620A: AstroSat CZTI detection
  87. The EP-WXT trigger 01709179396 is likely a flaring star CSTAR 38580
  88. GRB 241018A: Maidanak optical observations
  89. GRB 250620C: AstroSat CZTI detection
  90. Fermi GRB 250624A: Global MASTER-Net observations report
  91. GRB 250624A: Fermi GBM Final Real-time Localization
  92. sb25061207/GRB 250612D - SVOM/ECLAIRs refined analysis
  93. Fermi GRB 250623A: Global MASTER-Net observations report
  94. GRB 250623A: Fermi GBM Final Real-time Localization
  95. GRB 250521A: VZLUSAT-2 detection
  96. GRB 250617B: Swift-BAT refined analysis
  97. Fermi trigger No 772190032: Global MASTER-Net observations report
  98. Konus-Wind detection of GRB 250620C
  99. IPN triangulation of GRB 250620С (long/bright)
  100. GRB 250621B: SVOM/GRM detection of a possible magnetar X-ray burst

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