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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"

39163 results found.

  1. GRB 250902A: VZLUSAT-2 detection
  2. GRB 250903A: Swift-XRT observations
  3. GRB 250830C: VZLUSAT-2 detection
  4. GRB 250903A: VLT X-shooter spectroscopic redshift z = 1.590
  5. GRB 250903A: EP-FXT counterpart detection
  6. GRB 250902A: GECAM-B detection
  7. GRB 250903A: LCO optical observation
  8. GRB 250903A: LCO optical afterglow detection
  9. GRB 250903A: SVOM/VT optical confirmation with VHF data
  10. EP250901a: Mondy, Assy and SAO RAS optical limits
  11. Subject GRB 250903A: SVOM/MXT afterglow detection
  12. GRB 250903A: TRT optical counterpart detection
  13. GRB 250902B: AstroSat CZTI detection
  14. GRB 250903A: SVOM detection of a burst
  15. EP250903a: Global MASTER-Net observations report
  16. EP250903a: TRT optical observations
  17. EP 250827B: Detection of supernova counterpart by LCO.
  18. EP250827b / AT 2025wkm: TRT optical observations
  19. EP250827b: NOT spectroscopic observations and AT 2025wkm classification as a broad-lined type-Ic supernova
  20. GRB 250902B: SVOM/GRM observation
  21. GRB 250831A (SVOM trigger sb25083102): KAIT confirmation of stellar flare
  22. Fermi GRB 250902B: Global MASTER-Net observations report
  23. GRB 250902A: Fermi GBM Detection
  24. GRB 250901A: Swift/UVOT Upper Limit
  25. GRB 250902B: Fermi GBM Final Real-time Localization
  26. GRB 250830B: Swift-XRT afterglow detection
  27. GRB 250831A (SVOM trigger sb25083102): confirmation of a stellar flare by SVOM/VT
  28. GRB 250902A: SVOM/GRM observation
  29. GRB 250901A: EP-FXT follow-up observation
  30. GRB 250901A: NOT optical observations
  31. GRB 250902A: Fermi GBM Final Real-time Localization
  32. GRB 250901A: SVOM/VT optical afterglow with VHF data
  33. GRB 250901A: Swift-XRT afterglow detection
  34. GRB 250901A: LCO optical upper limit
  35. EP250831a: NOT optical observations and tentative afterglow candidate
  36. GRB 250901A: SVOM detection of a burst
  37. GRB 250831B: SVOM/GRM observation
  38. GRB 250830C: Insight-HXMT detection
  39. EP250901a: Mephisto optical upper limits
  40. GRB 250830C: GECAM-B detection
  41. EP250901a: Global MASTER-Net observations report
  42. GRB 250830C: AstroSat CZTI detection of a long burst
  43. IceCube Alert 250831.75: Global MASTER-Net observations report
  44. EP250831a: Global MASTER-Net observations report
  45. IceCube-250831A - IceCube observation of a high-energy neutrino candidate track-like event
  46. GRB 250831A (SVOM trigger sb25083102) is likely an outburst from star G 272-61
  47. GRB 250831A: Swift-XRT counterpart detection
  48. GRB 250831A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  49. GRB 250831A: SVOM/VT upper limit with VHF data
  50. GRB 250831A: SVOM detection of a soft burst
  51. GRB 250830B: Swift-XRT observations
  52. EP250830a: Global MASTER-Net observations report
  53. EP250830a/GRB 250830B: Einstein Probe detection of an X-ray transient and Swift/XRT follow-up
  54. GRB 250830B: Swift ToO observations
  55. GRB 250830B: MAXI/GSC detection
  56. GRB 250830A / MAXI J0853+337: MAXI/GSC detection
  57. GRB 250828B: Swift-BAT refined analysis
  58. GRB 250808B: SVOM detection of a burst through offline search
  59. Swift GRB 250828B: Global MASTER-Net observations report
  60. EP250828a: Global MASTER-Net observations report
  61. EP-WXT trigger 01709200800 : KAIT optical observations
  62. EP250828a: KAIT optical upper limit
  63. EP250828a: NOT optical counterpart confirmation
  64. GRB 250828B: Swift detection of a burst
  65. GRB 250828A: Fermi GBM Final Localization
  66. GRID detection of GRB 250824A
  67. Fermi GRB 250827A: Global MASTER-Net observations report
  68. EP250827a: confirmation of optical rebrightening with LCO
  69. EP250827a: GOTO observation of the optical afterglow
  70. GRB 250826A: SVOM/GRM observation
  71. GRB 250827A: Fermi GBM Final Real-time Localization
  72. EP250827A: An optical rebrightening was detected by LCO.
  73. EP250827a: TRT optical observations
  74. EP250827a / GRB 250827A: MASTER-OAFA OT observation
  75. EP250827a: Global MASTER-Net observations report
  76. Fermi GRB 250826A: Global MASTER-Net observations report
  77. GRB 250806A: HiPERCAM/GTC limits on a possible supernova
  78. LIGO/Virgo/KAGRA S250818k: SAO RAS BTA z-band observations of AT2025ulz
  79. Fermi trigger No 777883624: Global MASTER-Net observations report
  80. Fermi Gamma-ray Burst Monitor trigger 777883624/250826283 is not a GRB
  81. GRB 250826A: Fermi GBM Final Real-time Localization
  82. Fermi GRB 250824B: Global MASTER-Net observations report
  83. GRB 250823A: Swift-BAT refined analysis
  84. GRB 250821B: AstroSat CZTI detection
  85. GRB 250819A: AstroSat CZTI detection
  86. GRB 250821B: Insight-HXMT detection
  87. GRB 250823A: Swift-XRT refined Analysis
  88. GRB 250824B: Fermi GBM Final Real-time Localization
  89. GRB 250823A: COLIBRÍ optical observations
  90. GRB 250823A: SVOM/VT optical observation
  91. GRB 250824A: Fermi GBM Final Real-time Localization
  92. GRB 250823A: Swift/UVOT Detection
  93. GRB 250823A: NOT optical observations
  94. LIGO/Virgo/KAGRA S250818k: COLIBRÍ confirmation of rebrightening of AT2025ulz
  95. GRB 250823A: Fermi GBM Observation
  96. GRB 250818B: MeerKAT Detection
  97. GRB 250823A: Enhanced Swift-XRT position
  98. GRB 250823A: LCOGT Optical Detection
  99. GRB 250823A: BOOTES6/DPRT early optical detection
  100. GRB 250823A: Liverpool Telescope optical detection

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