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

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