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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 250628B: SVOM/VT optical upper limit
  2. GRB 250628B: EP-FXT counterpart detection
  3. LIGO/Virgo/KAGRA S250629bs: Updated Sky localization
  4. GRB 250627A: Insight-HXMT detection
  5. GRB 250627A: SVOM/GRM detection of a short burst
  6. LIGO/Virgo/KAGRA S250629ae: Updated Sky localization
  7. LIGO/Virgo/KAGRA S250629bs: Identification of a GW compact binary merger candidate
  8. LIGO/Virgo/KAGRA S250628am: Identification of a GW compact binary merger candidate (duplicate submission)
  9. LIGO/Virgo/KAGRA S250629ae: Identification of a GW compact binary merger candidate
  10. LIGO/Virgo/KAGRA S250628am: Updated Sky localization
  11. GRB 250628A: REM optical/NIR upper limits
  12. GRB 250628C: Fermi GBM Final Real-time Localization
  13. LIGO/Virgo/KAGRA S250628am: Identification of a GW compact binary merger candidate
  14. GRB 250628B: SVOM detection of a long burst
  15. Fermi Gamma-ray Burst Monitor trigger 772811638/250628579 is not a GRB
  16. GRB 250625A: VLT/X-shooter spectroscopic observations at the afterglow position
  17. GRB 250628A: VLT/X-shooter upper limits
  18. GRB 250628A: Swift/UVOT Upper Limits
  19. GRB 250628A: Swift-XRT refined Analysis
  20. Fermi GRB 250626A: Global MASTER-Net observations report
  21. Swift GRB 250628A: Global MASTER-Net observations report
  22. GRB 250628A: Enhanced Swift-XRT position
  23. GRB 250628A: Swift detection of a burst
  24. GRB 250625A: Swift-BAT refined analysis
  25. GRB 250625A: Leavitt Observatory afterglow detection
  26. Fermi Gamma-ray Burst Monitor trigger 772732642/250627665 is not a GRB
  27. Fermi Gamma-ray Burst Monitor trigger 772720540/250627525 is not a GRB
  28. GRB 250625A: AbAO and INASAN Kislovodsk Optical Observations
  29. The EP-WXT trigger 01709179435 is likely a new outburst of the CV SS Cyg
  30. GRB 250625A: GTC/OSIRIS+ spectroscopic observations of the potential host galaxy
  31. GRB 250626A: Fermi GBM Final Real-time Localization
  32. Fermi Gamma-ray Burst Monitor trigger 772647532/250626680 is not a GRB
  33. GRB 250625A: Osservatorio Astronomico "Nastro Verde" optical observations: detection of an optical counterpart
  34. GRB 250625A: SVOM/C-GFT upper limit in early phase
  35. GRB 250625A: GECAM-B detection
  36. GRB 250625A: Swift/UVOT Upper Limits
  37. GRB 250625A: ABObservatory afterglow detection
  38. GRB 250625A: OHP/T193 optical detection
  39. GRB 250625A: COLIBRÍ optical observations
  40. GRB 250625A: Fermi-LAT detection
  41. GRB 250625A: Swift-XRT refined Analysis
  42. GRB 250625A: JinShan optical observations
  43. GRB250625A: Fermi GBM Observation
  44. Swift GRB 250625A: Global MASTER-Net observations report
  45. GRB 250625A: NOT z-band upper limit
  46. GRB 250625A: SVOM/VT optical confirmation
  47. GRB 250620B: Fermi GBM Observation
  48. GRB 250625A: SAO RAS possible optical afterglow
  49. GRB 250625A: Enhanced Swift-XRT position
  50. Fermi GRB 250625A: Global MASTER-Net observations report
  51. GRB 250625A: Swift detection of a burst
  52. GRB 250625A: Fermi GBM Final Real-time Localization
  53. GRB 250617B: Mondy and SAO RAS optical observations on 2025-06-23, 2025-06-24
  54. GRB 250620A: AstroSat CZTI detection
  55. The EP-WXT trigger 01709179396 is likely a flaring star CSTAR 38580
  56. GRB 241018A: Maidanak optical observations
  57. GRB 250620C: AstroSat CZTI detection
  58. Fermi GRB 250624A: Global MASTER-Net observations report
  59. GRB 250624A: Fermi GBM Final Real-time Localization
  60. sb25061207/GRB 250612D - SVOM/ECLAIRs refined analysis
  61. Fermi GRB 250623A: Global MASTER-Net observations report
  62. GRB 250623A: Fermi GBM Final Real-time Localization
  63. GRB 250521A: VZLUSAT-2 detection
  64. GRB 250617B: Swift-BAT refined analysis
  65. Fermi trigger No 772190032: Global MASTER-Net observations report
  66. Konus-Wind detection of GRB 250620C
  67. IPN triangulation of GRB 250620С (long/bright)
  68. GRB 250621B: SVOM/GRM detection of a possible magnetar X-ray burst
  69. GRB 250620C: SVOM/GRM observation
  70. GRB 250620A: SVOM/GRM observation of a short burst
  71. GRB250620A: Fermi GBM Observation
  72. GRB 250617B: Calapai Observatory, Massa S. Giorgio (Messina), optical observation.
  73. Fermi GRB 250621A: Global MASTER-Net observations report
  74. GRB 250619B: Fermi GBM Observation
  75. GRB 250621A: Fermi GBM Final Real-time Localization
  76. GRB 250620B: Swift/BAT-GUANO localization skymap of a burst
  77. GRB250620C: Fermi GBM Observation
  78. GRB 250506A - SVOM/ECLAIRs Refined analysis
  79. The EP-WXT trigger 01709179071 is likely a flaring star
  80. GRB 250620A: Swift/BAT-GUANO subthreshold detection of a possibly short burst
  81. GRB 250619B: Swift/BAT-GUANO localization skymap of a burst
  82. GRB 250620C: Fermi GBM Final Real-time Localization
  83. Fermi trigger No 772128434: Global MASTER-Net observations report
  84. GRB 250620B: Fermi GBM Final Real-time Localization
  85. GRB 250620A: Fermi GBM Final Real-time Localization
  86. EP-WXT trigger 01709179036: a new outburst of GRS 1739-278
  87. GRB 250617B: Nickel telescope optical observations
  88. GRB 250619B: Fermi GBM Final Real-time Localization
  89. Fermi trigger No 772058337: Global MASTER-Net observations report
  90. Fermi Gamma-ray Burst Monitor trigger 772058337/250619860 is not a GRB
  91. GRB 250615A: Kilonova-Catcher optical upper limits
  92. GRB 250619A: Fermi GBM Final Real-time Localization
  93. GRB 250617B: Assy AZT-20 Optical Observations
  94. GRB 250612A / Swift J1643.6−3854: Swift-BAT refined analysis
  95. Fermi GRB 250617A: Global MASTER-Net observations report
  96. GRB 250615A/EP250615a: FTW optical and NIR observations
  97. sb25061218/SVOM: OHP/T120 and OHP/T193 optical imaging and spectroscopic observations
  98. GRB 250617B: Swift/UVOT Detection
  99. GRB 250617B: Kilonova-Catcher optical afterglow detection
  100. GRB 250617B: VLT/X-shooter spectroscopic redshift z = 1.396

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