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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. LIGO/Virgo/KAGRA S250628am: Updated Sky localization
  2. GRB 250628A: REM optical/NIR upper limits
  3. GRB 250628C: Fermi GBM Final Real-time Localization
  4. LIGO/Virgo/KAGRA S250628am: Identification of a GW compact binary merger candidate
  5. GRB 250628B: SVOM detection of a long burst
  6. Fermi Gamma-ray Burst Monitor trigger 772811638/250628579 is not a GRB
  7. GRB 250625A: VLT/X-shooter spectroscopic observations at the afterglow position
  8. GRB 250628A: VLT/X-shooter upper limits
  9. GRB 250628A: Swift/UVOT Upper Limits
  10. GRB 250628A: Swift-XRT refined Analysis
  11. Fermi GRB 250626A: Global MASTER-Net observations report
  12. Swift GRB 250628A: Global MASTER-Net observations report
  13. GRB 250628A: Enhanced Swift-XRT position
  14. GRB 250628A: Swift detection of a burst
  15. GRB 250625A: Swift-BAT refined analysis
  16. GRB 250625A: Leavitt Observatory afterglow detection
  17. Fermi Gamma-ray Burst Monitor trigger 772732642/250627665 is not a GRB
  18. Fermi Gamma-ray Burst Monitor trigger 772720540/250627525 is not a GRB
  19. GRB 250625A: AbAO and INASAN Kislovodsk Optical Observations
  20. The EP-WXT trigger 01709179435 is likely a new outburst of the CV SS Cyg
  21. GRB 250625A: GTC/OSIRIS+ spectroscopic observations of the potential host galaxy
  22. GRB 250626A: Fermi GBM Final Real-time Localization
  23. Fermi Gamma-ray Burst Monitor trigger 772647532/250626680 is not a GRB
  24. GRB 250625A: Osservatorio Astronomico "Nastro Verde" optical observations: detection of an optical counterpart
  25. GRB 250625A: SVOM/C-GFT upper limit in early phase
  26. GRB 250625A: GECAM-B detection
  27. GRB 250625A: Swift/UVOT Upper Limits
  28. GRB 250625A: ABObservatory afterglow detection
  29. GRB 250625A: OHP/T193 optical detection
  30. GRB 250625A: COLIBRÍ optical observations
  31. GRB 250625A: Fermi-LAT detection
  32. GRB 250625A: Swift-XRT refined Analysis
  33. GRB 250625A: JinShan optical observations
  34. GRB250625A: Fermi GBM Observation
  35. Swift GRB 250625A: Global MASTER-Net observations report
  36. GRB 250625A: NOT z-band upper limit
  37. GRB 250625A: SVOM/VT optical confirmation
  38. GRB 250620B: Fermi GBM Observation
  39. GRB 250625A: SAO RAS possible optical afterglow
  40. GRB 250625A: Enhanced Swift-XRT position
  41. Fermi GRB 250625A: Global MASTER-Net observations report
  42. GRB 250625A: Swift detection of a burst
  43. GRB 250625A: Fermi GBM Final Real-time Localization
  44. GRB 250617B: Mondy and SAO RAS optical observations on 2025-06-23, 2025-06-24
  45. GRB 250620A: AstroSat CZTI detection
  46. The EP-WXT trigger 01709179396 is likely a flaring star CSTAR 38580
  47. GRB 241018A: Maidanak optical observations
  48. GRB 250620C: AstroSat CZTI detection
  49. Fermi GRB 250624A: Global MASTER-Net observations report
  50. GRB 250624A: Fermi GBM Final Real-time Localization
  51. sb25061207/GRB 250612D - SVOM/ECLAIRs refined analysis
  52. Fermi GRB 250623A: Global MASTER-Net observations report
  53. GRB 250623A: Fermi GBM Final Real-time Localization
  54. GRB 250521A: VZLUSAT-2 detection
  55. GRB 250617B: Swift-BAT refined analysis
  56. Fermi trigger No 772190032: Global MASTER-Net observations report
  57. Konus-Wind detection of GRB 250620C
  58. IPN triangulation of GRB 250620C (long/bright)
  59. GRB 250621B: SVOM/GRM detection of a possible magnetar X-ray burst
  60. GRB 250620C: SVOM/GRM observation
  61. GRB 250620A: SVOM/GRM observation of a short burst
  62. GRB250620A: Fermi GBM Observation
  63. GRB 250617B: Calapai Observatory, Massa S. Giorgio (Messina), optical observation.
  64. Fermi GRB 250621A: Global MASTER-Net observations report
  65. GRB 250619B: Fermi GBM Observation
  66. GRB 250621A: Fermi GBM Final Real-time Localization
  67. GRB 250620B: Swift/BAT-GUANO localization skymap of a burst
  68. GRB250620C: Fermi GBM Observation
  69. GRB 250506A - SVOM/ECLAIRs Refined analysis
  70. The EP-WXT trigger 01709179071 is likely a flaring star
  71. GRB 250620A: Swift/BAT-GUANO subthreshold detection of a possibly short burst
  72. GRB 250619B: Swift/BAT-GUANO localization skymap of a burst
  73. GRB 250620C: Fermi GBM Final Real-time Localization
  74. Fermi trigger No 772128434: Global MASTER-Net observations report
  75. GRB 250620B: Fermi GBM Final Real-time Localization
  76. GRB 250620A: Fermi GBM Final Real-time Localization
  77. EP-WXT trigger 01709179036: a new outburst of GRS 1739-278
  78. GRB 250617B: Nickel telescope optical observations
  79. GRB 250619B: Fermi GBM Final Real-time Localization
  80. Fermi trigger No 772058337: Global MASTER-Net observations report
  81. Fermi Gamma-ray Burst Monitor trigger 772058337/250619860 is not a GRB
  82. GRB 250615A: Kilonova-Catcher optical upper limits
  83. GRB 250619A: Fermi GBM Final Real-time Localization
  84. GRB 250617B: Assy AZT-20 Optical Observations
  85. GRB 250612A / Swift J1643.6−3854: Swift-BAT refined analysis
  86. Fermi GRB 250617A: Global MASTER-Net observations report
  87. GRB 250615A/EP250615a: FTW optical and NIR observations
  88. sb25061218/SVOM: OHP/T120 and OHP/T193 optical imaging and spectroscopic observations
  89. GRB 250617B: Swift/UVOT Detection
  90. GRB 250617B: Kilonova-Catcher optical afterglow detection
  91. GRB 250617B: VLT/X-shooter spectroscopic redshift z = 1.396
  92. GRB 250617B: COLIBRÍ optical observations
  93. GRB 250617B: NOT NIR observations of the afterglow
  94. GRB 250617B: Swift-XRT refined Analysis
  95. GRB 250617B: SVOM/VT optical observation
  96. GRB 250617B: NUTTelA-TAO early time optical observations
  97. Fermi trigger No 771886893: Global MASTER-Net observations report
  98. Swift GRB 250617B: Global MASTER-Net observations report
  99. GRB 250617B: GOTO optical upper limit
  100. GRB 250617B: Enhanced Swift-XRT position

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