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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"

39162 results found.

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

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