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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"

2803 results found.

  1. Konus-Wind detection of GRB 260921A (possible merger-origin)
  2. GRB 260921A: Fermi GBM Observation
  3. Swift GRB 260921A: MASTER OT J094129.58+025052.5 possible optical counterpart detection with host galaxy (z=1.3)
  4. GRB 260921A: Swift detection of a burst
  5. EP260920b: COLIBRÍ optical observations
  6. GRB 260918A: SVOM detection of a burst
  7. GRB 260914A: SVOM/GRM observation
  8. GRB 260914A: SVOM/COLIBRÍ (FM-GFT) possible optical counterpart candidate
  9. GRB 260831B: SVOM detection of a possible burst
  10. GRB 260818B: 6 GHz VLA observations
  11. GRB 260818B: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate
  12. GRB 260807A: EP-FXT follow-up observations
  13. GRB 260822A: SVOM/COLIBRÍ (FM-GFT) possible optical counterpart candidate
  14. GRB 260818B: SVOM/ECLAIRs refined analysis
  15. GRB 260818A: SVOM/ECLAIRs refined analysis
  16. GRB 260818A: SVOM possible detection of a long and faint GRB
  17. EP260812b: GTC/OSIRIS+ tentative spectroscopic redshift z = 2.034
  18. GRB 260805D: SVOM/GRM detection of a possible magnetar burst
  19. EP260812a: NOT and Liverpool Telescope upper limits:
  20. EP260812b: Einstein Probe detection of an X-ray transient
  21. GRB 260317A: SVOM/ECLAIRs detection through offline targeted search and its possible association to magnetar 1E 1841-04.5
  22. GRB 260807A: SVOM/ECLAIRs refined analysis
  23. GRB 260808B: SVOM/ECLAIRs refined analysis
  24. GRB 260807A: SVOM possible detection of a faint burst
  25. GRB 260708A / SN 2026stf: Spectroscopic host redshift z = 0.055 and confirmation of an associated type Ic-BL supernova
  26. GRB 260802A / EP J223759.5+531421: SVOM/VT optical upper limit
  27. GRB 260802A/EP J223759.5+531421: SVOM detection of a possible magnetar burst
  28. GRB 260726A: SVOM ECLAIRs improved position and MXT possible detection of a counterpart
  29. IceCube-260722A: Classification of ZTF26abjbxfs/SN 2026vts as a Type Ia Supernova
  30. GRB 260706A: ATCA detection of possible radio counterpart
  31. GRB 260705A: ATCA radio observations
  32. GRB 260705A: Candidate Optical Counterpart from SOAR and Gemini-South and Possible Association with GRB 260705B
  33. GRB 260704A: SVOM/COLIBRÍ (FM-GFT) possible optical counterpart candidate
  34. GRB 260704A: SVOM detection of a possible GRB
  35. GRB 260618A: Fermi GBM Observation
  36. GRB 260618C: SVOM/ECLAIRs detection of a possible burst through on-ground search
  37. GRB 260610B: VLT/FORS2 spectroscopic observation suggests the non-thermal nature of the optical rebrightening
  38. GRB 260619A: SVOM possible detection of a faint burst
  39. Konus-Wind detection of GRB 260616A
  40. GRB 260610B / AT2026owq: SAO RAS optical observations of possible re-brightening
  41. GRB260616C: MAXI/GSC detection
  42. GRB 260610B / AT 2026owq: Possible re-brightening identified from Pan-STARRS observations
  43. GRB 260610B / AT2026owq: SVOM/VT optical observations
  44. GRB 260610B / AT 2026owq: COLIBRÍ optical observations
  45. GRB 260610B / AT2026owq: Early ATLAS observations
  46. GRB 260604C: GRANDMA further observations
  47. GRB 260604C: Mondy optical observations: evidence of a possible brightening
  48. GRB 260603A: SVOM/COLIBRÍ (FM-GFT) photometric redshift z = 3.57
  49. EP260602a: COLIBRÍ optical observations
  50. GRB 260601B/EP260601a: Insight-HXMT detection
  51. GRB 260601B/EP260601a: GECAM-B analysis suggests a possible long duration Type I burst
  52. GRB 260601B: GECAM-B detection of a burst probably associated with EP260601a
  53. GRB 260530B: SVOM/GRM detection of a possible bright short GRB
  54. EP260527a/GRB 260527A: optical upper limit with Kinder observations
  55. GRB 260527A/EP260527a: FTW optical and NIR observations
  56. GRB 260527A: GECAM-B detection of a short burst probably associated with EP260527a
  57. GRB 260516D: GOTO optical counterpart detection
  58. GRB 260516D: GROWTH-India Telescope optical detection
  59. GRB 260516D: SVOM possible detection of a burst
  60. EP260507a: Kinder optical counterpart candidate
  61. GRB 260310A / AT2026fgk: photometric monitoring and tentative maximum of a possible SN
  62. GRB 260504B: SVOM detection of a short burst
  63. GRB 260428A: SVOM/GRM observation of a possible short burst with extended emission
  64. GRB 260428A: GECAM-B detection of a possible long duration Type I burst
  65. EP260417a/GRB 260417A: refined analysis of the EP-WXT and follow-up EP-FXT observations
  66. GRB 260411B: COLIBRÍ optical observations
  67. GRB 260407B: SVOM/GRM detection of a possible magnetar X-ray burst
  68. EP260321a: uGMRT observations
  69. EP260329a: EP-FXT follow up observation
  70. EP260321a: Upper limits from a neutrino search with IceCube
  71. EP260321a: VLT imaging and spectroscopy show the variable source to be at z = 0.0343
  72. EP260321a: further Kinder optical observations
  73. EP260321a: refined analysis of the EP-WXT and EP-FXT observations, implying a possible supernova shock breakout candidate
  74. GRB 260310A / AT 2026fgk: COLIBRÍ evidence of a late rebrightening
  75. EP260314a: COLIBRÍ optical upper limit
  76. GRB 260310A / AT 2026fgk: COLIBRÍ continuing optical observations
  77. GRB 260310A/AT 2026fgk: Bok spectroscopic observation
  78. GRB 260310A / AT 2026fgk: COLIBRÍ optical observations
  79. GRB 260307B: possible NOT optical counterpart
  80. GRB 260207A: TESS Detection and Possible VLA Counterpart
  81. SVOM/sb26030408: SVOM detection of an X-ray transient likely associated with Beta Persei
  82. GRB 260303A: SVOM detection of a burst
  83. EP260214a: VLA 6 GHz detection
  84. GRB 260204A: SVOM/ECLAIRs refined analysis
  85. EP260128a: Liverpool Telescope optical observations and possible counterpart
  86. GRB 251208D: SVOM/ECLAIRs refined analysis
  87. GRB 251208D: SVOM/ECLAIRs refined analysis
  88. GRB 260109C: LCO optical upper limits
  89. Swift Trigger 1434591: possible GRB 260109C
  90. GRB 260103A: SVOM/GRM observation of a possible GRB
  91. GRB 251230A / EP251230a: further NOT optical observations revealing shallower decay or possible rebrightening
  92. GRB 251230A/EP251230a: Optical upper limit with Kinder observations
  93. IceCube-251225A - IceCube observation of a high-energy neutrino candidate track-like event
  94. GRB 251129A / EP251129a: VLA detection of a radio counterpart
  95. GRB 251219A: GECAM-B detection of a possible magnetar X-ray burst from SGR 1830-0645
  96. IceCube-251218A - IceCube observation of a high-energy neutrino candidate track-like event
  97. EP251214a: EP-WXT detection of an X-ray transient possibly associated with GRB 251214A
  98. IceCube-251210A - IceCube observation of a high-energy neutrino candidate track-like event
  99. GRB 251208D: SVOM possible detection of a faint burst
  100. Swift GRB 251205A : MASTER OT detection with host galaxy

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