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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"

26983 results found.

  1. Fermi GBM Sub-Threshold Detection of GRB 260321A
  2. EP260321a: Kinder observations detect a blue variable star and set limits on a source from the z =0.034 galaxy within the error circle
  3. EP260321a: Global MASTER-Net observations report
  4. EP260321a: Einstein Probe detection of an X-ray transient
  5. GRB 260318A: Glowbug gamma-ray detection
  6. GRB 260310A / AT 2026fgk: KAIT optical observations
  7. GRB 260320A: NuSTAR detection of prompt emission
  8. EP-WXT trigger 01709258989: KAIT confirmation of a stellar flare
  9. GRB 260310A: no evidence of re-brightening up to 9.6 days in optical observation at Mondy
  10. GRB 260310A / AT 2026fgk: COLIBRÍ evidence of a late rebrightening
  11. EP-WXT trigger 01709258989: confirmation of a stellar flare by BOOTES-7
  12. GRB 260318A: SVOM/GRM observation
  13. GRB 260310A: classification as long GRB based on Eiso, Ep, and T_90
  14. GRB260310A/AT2026fgk: Further optical observation from 1.3m DFOT
  15. Fermi GRB 260318A: Global MASTER-Net observations report
  16. GRB 260316A / EP260316a: COLIBRÍ optical followup of counterpart candidate
  17. GRB 260310A / AT 2026fgk: radio detection with the VLA
  18. GRB 260310A / AT2026fgk: SVOM/VT optical observations
  19. GRB 260310A / AT2026fgk: LCO optical observations
  20. GRB 260316B: SVOM/GRM observation
  21. EP260316a / GRB 260316A: SVOM/VT optical upper limits
  22. EP260316a: COLIBRÍ faint optical counterpart candidate
  23. Fermi-LAT Gamma-ray Observations of IceCube-260315A
  24. EP260316a: refined analysis of the EP-WXT and EP-FXT observations
  25. IceCube-260315A: Upper limits from a search for additional neutrino events in IceCube
  26. EP260316a: Xinglong optical upper limit
  27. EP260316a: optical upper limit with Kinder observations
  28. EP260316a / GRB 260316A : Fermi-GBM Sub-Threshold Detection
  29. GRB 260314A: Glowbug gamma-ray detection
  30. The EP-WXT trigger 00199258890 (EP260316a): a correction to the trigger time and FXT automatic follow-up
  31. IceCube-260315A: COLIBRÍ optical observations
  32. EP260314a: Xinglong optical upper limit
  33. EP260314a: optical upper limit with Kinder observations
  34. IceCube Alert-260315A/AT2026fpm Automatic MASTER optical blue counterpart candidate
  35. GRB 260310A / AT2026fgk: 1.3m DFOT optical observations
  36. GRB 260310A / AT 2026fgk: iTelescope optical observations
  37. EP260314a: COLIBRÍ optical upper limit
  38. EP260314a: refined analysis of the EP-WXT and EP-FXT observations
  39. EP260314a: Global MASTER-Net observations report
  40. EP260314a: SVOM/VT optical candidate
  41. Fermi trigger No 795185313: Global MASTER-Net observations report
  42. IceCube Alert 260315A: Global MASTER-Net observations report
  43. EP260314a: Einstein Probe detection of an X-ray transient
  44. GRB 260310A / AT2026fgk: SAO RAS optical observations
  45. GRB 260310A / AT2026fgk: Multiband optical follow-up with Kinder observations
  46. GRB 260310A / AT 2026fgk: COLIBRÍ continuing optical observations
  47. Fermi GRB 260314A: Global MASTER-Net observations report
  48. Fermi GRB 260313A: Global MASTER-Net observations report
  49. GRB 260310A/AT 2026fgk: WINTER NIR Detections
  50. GRB 260310A/AT 2026fgk: J-band observations by the SYSU 80 cm infrared telescope
  51. GRB 260310A/AT 2026fgk: DDOTI Optical Detection
  52. GRB 260312B: AstroSat CZTI detection
  53. GRB 260310A / AT2026fgk: OSIRIS+/GTC spectroscopy confirms redshift z = 0.153
  54. GRB 260310A / AT 2026fgk: COLIBRÍ optical observations
  55. GRB 260310A / AT2026fgk : MASTER OT rebrightening during 7h observations
  56. GRB 260312B: Glowbug gamma-ray detection
  57. GRB 260310A: Fermi GBM Observation
  58. GRB 260310A: potential optical counterpart
  59. Fermi GRB 260312B: Global MASTER-Net observations report
  60. Fermi GRB 260311B: Global MASTER-Net observations report
  61. GRB 260312B: BALROG localization (Fermi Trigger 795001611 / GRB 260312407)
  62. GRB 260131A/B: radio detection with the VLA
  63. EP260302a: MeerKAT radio counterpart
  64. GRB 260308A: SVOM/GRM observation of a short GRB
  65. EP260306a: Mondy optical upper limit
  66. Fermi GRB 260310B: Global MASTER-Net observations report
  67. Fermi GRB 260310A: Global MASTER-Net observations report
  68. GRB 260208A: radio detection with the VLA
  69. GRB 260307A: Glowbug gamma-ray detection
  70. Fermi GBM Sub-Threshold Detection of GRB 260307B
  71. GRB 260307B: Mephisto optical upper limits
  72. GRB 260307B: possible NOT optical counterpart
  73. GRB 260307B: SVOM/VT upper limit with X band data analysis
  74. Fermi GRB 260307A: Global MASTER-Net observations report
  75. GRB260307B: GROWTH-India Telescope optical upper limit
  76. GRB 260307B: SVOM/VT optical candidate
  77. GRB 260307B: SVOM/C-GFT upper limit
  78. GRB 260307B: SVOM detection of a burst
  79. EP260306a: refined analysis of the EP-WXT and EP-FXT observations
  80. GRB 260207A: TESS Detection and Possible VLA Counterpart
  81. EP260302a: SVOM/VT optical observation
  82. EP260306a: Gemini-North redshift z = 4.773
  83. EP260306a: SVOM/VT optical observation
  84. EP260302a: Gemini-South redshift z = 1.535
  85. EP260306a: COLIBRÍ optical observations of the fading and red counterpart
  86. EP260306a: Einstein Probe detection of an X-ray transient
  87. EP260302a: Optical afterglow rebrightening
  88. GRB 260228A: further EP-FXT observations and X-ray afterglow confirmation
  89. GRB 260303A: 1.3m DFOT optical upper limit
  90. Fermi GRB 260305A: Global MASTER-Net observations report
  91. GRB 260303B: AstroSat CZTI detection
  92. GRB 260303A: SVOM/VT optical observations
  93. GRB 260303A: J-band observations with WINTER
  94. GRB 260303B: NuSTAR detection of prompt emission
  95. EP260302a: Global MASTER-Net observations report
  96. Fermi GRB 260303B: Global MASTER-Net observations report
  97. GRB 260303B: BALROG localization (Fermi Trigger 794237065 / GRB 260303559)
  98. EP260302a: analysis of the follow-up EP-FXT observation
  99. EP260302a: LCO observations
  100. EP260302a: BOOTES-7 optical counterpart detection at early times

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