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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 250424A: VIRT Optical Upper Limit
  2. GRBs 250702B/C/D/E / EP250702a: Swift XRT localization
  3. GRB 250702B,C,D,E/EP250702a: COLIBRÍ optical upper limit
  4. EP250702a/GRB 250702B, C, D, E: EP-FXT follow-up observation
  5. GRB 250702F: TRT Optical Observation
  6. GRB 250703A: DDOTI Optical Upper Limit
  7. GRBs 250702B,C,D,E / EP250702a: Konus-Wind detection of a hard X-ray transient activity
  8. GRB 250702F: REM optical afterglow detection
  9. EP250702a: Global MASTER-Net observations report
  10. GRB 250702F: DDOTI Optical Observation
  11. GRB 250702B,C,D,E / EP 250702: MAXI/GSC detection
  12. GRB 250703A: Fermi GBM Final Real-time Localization
  13. EP250702a/GRB 250702B,C,D,E: GOTO optical upper limits
  14. GRB 250702F: COLIBRÍ Observations of the Afterglow
  15. EP250702a : an X-ray transient detected by Einstein Probe likely associated with GRB 250702B,C,D,E
  16. Fermi GRB 250702E: Global MASTER-Net observations report
  17. Fermi GRB 250702B: Global MASTER-Net observations report
  18. GRB 250702D, C, E: Swift/BAT-GUANO localization skymap of a burst or galactic transient
  19. GRB 250702F: Enhanced Swift-XRT position
  20. GRB 250702F: GTC/OSIRIS+ spectroscopic redshift z = 1.520
  21. GRB 250702F: NOT observations of the optical afterglow
  22. GRB 250702F: MASTER optical afterglow observation
  23. Fermi GRB 250702F: Global MASTER-Net observations report
  24. Fermi GRB 250702C: Global MASTER-Net observations report
  25. GRB 250702F: GOTO optical counterpart detection
  26. GRB 250702F: Ondrejov D50 optical afterglow detection
  27. GRB 250702F: Swift detection of a burst with an optical counterpart
  28. Swift GRB250702.88: Global MASTER-Net observations report
  29. GRB 250702F: Fermi GBM Final Real-time Localization
  30. Fermi GBM Triggers 250702B, C, D and E are likely from the same source
  31. GRB 250702E: Fermi GBM Final Real-time Localization
  32. Konus-Wind detection of GRB 250627A
  33. IPN triangulation of GRB 250627A (short)
  34. GRB 250702A: Fermi GBM Detection
  35. GRB 250702D: Fermi GBM Final Localization Correction
  36. GRB 250702C: Fermi GBM Final Real-time Localization
  37. LIGO/Virgo/KAGRA S250702n: Identification of a GW compact binary merger candidate
  38. GRB 250702B: Fermi GBM Final Real-time Localization
  39. GRB 250702A: BALROG localization (Fermi Trigger 773142852 / GRB 250702413)
  40. GRB 250702A: Fermi GBM Final Real-time Localization
  41. LIGO/Virgo/KAGRA S250701bq: Identification of a GW compact binary merger candidate
  42. LIGO/Virgo/KAGRA S250701bp: Identification of a GW compact binary merger candidate
  43. Fermi Gamma-ray Burst Monitor trigger 772838080/250628885 is not a GRB
  44. GRB 250628B: Swift-XRT observations
  45. Fermi Gamma-ray Burst Monitor trigger 772981768/250630548 is not a GRB
  46. GRB 250628B: SVOM/VT optical upper limit
  47. GRB 250628B: EP-FXT counterpart detection
  48. LIGO/Virgo/KAGRA S250629bs: Updated Sky localization
  49. GRB 250627A: Insight-HXMT detection
  50. GRB 250627A: SVOM/GRM detection of a short burst
  51. LIGO/Virgo/KAGRA S250629ae: Updated Sky localization
  52. LIGO/Virgo/KAGRA S250629bs: Identification of a GW compact binary merger candidate
  53. LIGO/Virgo/KAGRA S250628am: Identification of a GW compact binary merger candidate (duplicate submission)
  54. LIGO/Virgo/KAGRA S250629ae: Identification of a GW compact binary merger candidate
  55. LIGO/Virgo/KAGRA S250628am: Updated Sky localization
  56. GRB 250628A: REM optical/NIR upper limits
  57. GRB 250628C: Fermi GBM Final Real-time Localization
  58. LIGO/Virgo/KAGRA S250628am: Identification of a GW compact binary merger candidate
  59. GRB 250628B: SVOM detection of a long burst
  60. Fermi Gamma-ray Burst Monitor trigger 772811638/250628579 is not a GRB
  61. GRB 250625A: VLT/X-shooter spectroscopic observations at the afterglow position
  62. GRB 250628A: VLT/X-shooter upper limits
  63. GRB 250628A: Swift/UVOT Upper Limits
  64. GRB 250628A: Swift-XRT refined Analysis
  65. Fermi GRB 250626A: Global MASTER-Net observations report
  66. Swift GRB 250628A: Global MASTER-Net observations report
  67. GRB 250628A: Enhanced Swift-XRT position
  68. GRB 250628A: Swift detection of a burst
  69. GRB 250625A: Swift-BAT refined analysis
  70. GRB 250625A: Leavitt Observatory afterglow detection
  71. Fermi Gamma-ray Burst Monitor trigger 772732642/250627665 is not a GRB
  72. Fermi Gamma-ray Burst Monitor trigger 772720540/250627525 is not a GRB
  73. GRB 250625A: AbAO and INASAN Kislovodsk Optical Observations
  74. The EP-WXT trigger 01709179435 is likely a new outburst of the CV SS Cyg
  75. GRB 250625A: GTC/OSIRIS+ spectroscopic observations of the potential host galaxy
  76. GRB 250626A: Fermi GBM Final Real-time Localization
  77. Fermi Gamma-ray Burst Monitor trigger 772647532/250626680 is not a GRB
  78. GRB 250625A: Osservatorio Astronomico "Nastro Verde" optical observations: detection of an optical counterpart
  79. GRB 250625A: SVOM/C-GFT upper limit in early phase
  80. GRB 250625A: GECAM-B detection
  81. GRB 250625A: Swift/UVOT Upper Limits
  82. GRB 250625A: ABObservatory afterglow detection
  83. GRB 250625A: OHP/T193 optical detection
  84. GRB 250625A: COLIBRÍ optical observations
  85. GRB 250625A: Fermi-LAT detection
  86. GRB 250625A: Swift-XRT refined Analysis
  87. GRB 250625A: JinShan optical observations
  88. GRB250625A: Fermi GBM Observation
  89. Swift GRB 250625A: Global MASTER-Net observations report
  90. GRB 250625A: NOT z-band upper limit
  91. GRB 250625A: SVOM/VT optical confirmation
  92. GRB 250620B: Fermi GBM Observation
  93. GRB 250625A: SAO RAS possible optical afterglow
  94. GRB 250625A: Enhanced Swift-XRT position
  95. Fermi GRB 250625A: Global MASTER-Net observations report
  96. GRB 250625A: Swift detection of a burst
  97. GRB 250625A: Fermi GBM Final Real-time Localization
  98. GRB 250617B: Mondy and SAO RAS optical observations on 2025-06-23, 2025-06-24
  99. GRB 250620A: AstroSat CZTI detection
  100. The EP-WXT trigger 01709179396 is likely a flaring star CSTAR 38580

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