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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"

27001 results found.

  1. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limits at the FXT positions
  2. EP-WXT trigger 01709259112: confirmation of a stellar flare by BOOTES-5 & BOOTES-7
  3. Fermi GRB 260323A: Global MASTER-Net observations report
  4. GRB260310A: Palomar 60-inch photometry of an extremely bright late-time afterglow with a temporal break at 8 days
  5. GRB 260320A: Glowbug gamma-ray detection
  6. EP260321a: COLIBRÍ further optical observations and brightening
  7. EP260321a: Continued brightening from Kinder follow-up of the emerging supernova candidate
  8. EP260321a: Early TRT rising followed by JinShan decaying and then re-rising
  9. GRB 260321A: EP-FXT follow-up observation
  10. EP260321a: GOTO detection of blue variable source
  11. EP260321a: VLT imaging and spectroscopy show the variable source to be at z = 0.0343
  12. EP260321a: further Kinder optical observations
  13. GRB 260321A: SVOM/VT optical upper limits
  14. EP260321a: Las Cumbres upper limit
  15. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  16. EP260321a: COLIBRÍ optical upper limit on any supernova shock breakout emission
  17. EP260321a: refined analysis of the EP-WXT and EP-FXT observations, implying a possible supernova shock breakout candidate
  18. EP260321a: SVOM/VT optical upper limit
  19. Fermi GBM Sub-Threshold Detection of GRB 260321A
  20. EP260321a: Kinder observations detect a blue variable star and set limits on a source from the z =0.034 galaxy within the error circle
  21. EP260321a: Global MASTER-Net observations report
  22. EP260321a: Einstein Probe detection of an X-ray transient
  23. GRB 260318A: Glowbug gamma-ray detection
  24. GRB 260310A / AT 2026fgk: KAIT optical observations
  25. GRB 260320A: NuSTAR detection of prompt emission
  26. EP-WXT trigger 01709258989: KAIT confirmation of a stellar flare
  27. GRB 260310A: no evidence of re-brightening up to 9.6 days in optical observation at Mondy
  28. GRB 260310A / AT 2026fgk: COLIBRÍ evidence of a late rebrightening
  29. EP-WXT trigger 01709258989: confirmation of a stellar flare by BOOTES-7
  30. GRB 260318A: SVOM/GRM observation
  31. GRB 260310A: classification as long GRB based on Eiso, Ep, and T_90
  32. GRB260310A/AT2026fgk: Further optical observation from 1.3m DFOT
  33. Fermi GRB 260318A: Global MASTER-Net observations report
  34. GRB 260316A / EP260316a: COLIBRÍ optical followup of counterpart candidate
  35. GRB 260310A / AT 2026fgk: radio detection with the VLA
  36. GRB 260310A / AT2026fgk: SVOM/VT optical observations
  37. GRB 260310A / AT2026fgk: LCO optical observations
  38. GRB 260316B: SVOM/GRM observation
  39. EP260316a / GRB 260316A: SVOM/VT optical upper limits
  40. EP260316a: COLIBRÍ faint optical counterpart candidate
  41. Fermi-LAT Gamma-ray Observations of IceCube-260315A
  42. EP260316a: refined analysis of the EP-WXT and EP-FXT observations
  43. IceCube-260315A: Upper limits from a search for additional neutrino events in IceCube
  44. EP260316a: Xinglong optical upper limit
  45. EP260316a: optical upper limit with Kinder observations
  46. EP260316a / GRB 260316A : Fermi-GBM Sub-Threshold Detection
  47. GRB 260314A: Glowbug gamma-ray detection
  48. The EP-WXT trigger 00199258890 (EP260316a): a correction to the trigger time and FXT automatic follow-up
  49. IceCube-260315A: COLIBRÍ optical observations
  50. EP260314a: Xinglong optical upper limit
  51. EP260314a: optical upper limit with Kinder observations
  52. IceCube Alert-260315A/AT2026fpm Automatic MASTER optical blue counterpart candidate
  53. GRB 260310A / AT2026fgk: 1.3m DFOT optical observations
  54. GRB 260310A / AT 2026fgk: iTelescope optical observations
  55. EP260314a: COLIBRÍ optical upper limit
  56. EP260314a: refined analysis of the EP-WXT and EP-FXT observations
  57. EP260314a: Global MASTER-Net observations report
  58. EP260314a: SVOM/VT optical candidate
  59. Fermi trigger No 795185313: Global MASTER-Net observations report
  60. IceCube Alert 260315A: Global MASTER-Net observations report
  61. EP260314a: Einstein Probe detection of an X-ray transient
  62. GRB 260310A / AT2026fgk: SAO RAS optical observations
  63. GRB 260310A / AT2026fgk: Multiband optical follow-up with Kinder observations
  64. GRB 260310A / AT 2026fgk: COLIBRÍ continuing optical observations
  65. Fermi GRB 260314A: Global MASTER-Net observations report
  66. Fermi GRB 260313A: Global MASTER-Net observations report
  67. GRB 260310A/AT 2026fgk: WINTER NIR Detections
  68. GRB 260310A/AT 2026fgk: J-band observations by the SYSU 80 cm infrared telescope
  69. GRB 260310A/AT 2026fgk: DDOTI Optical Detection
  70. GRB 260312B: AstroSat CZTI detection
  71. GRB 260310A / AT2026fgk: OSIRIS+/GTC spectroscopy confirms redshift z = 0.153
  72. GRB 260310A / AT 2026fgk: COLIBRÍ optical observations
  73. GRB 260310A / AT2026fgk : MASTER OT rebrightening during 7h observations
  74. GRB 260312B: Glowbug gamma-ray detection
  75. GRB 260310A: Fermi GBM Observation
  76. GRB 260310A: potential optical counterpart
  77. Fermi GRB 260312B: Global MASTER-Net observations report
  78. Fermi GRB 260311B: Global MASTER-Net observations report
  79. GRB 260312B: BALROG localization (Fermi Trigger 795001611 / GRB 260312407)
  80. GRB 260131A/B: radio detection with the VLA
  81. EP260302a: MeerKAT radio counterpart
  82. GRB 260308A: SVOM/GRM observation of a short GRB
  83. EP260306a: Mondy optical upper limit
  84. Fermi GRB 260310B: Global MASTER-Net observations report
  85. Fermi GRB 260310A: Global MASTER-Net observations report
  86. GRB 260208A: radio detection with the VLA
  87. GRB 260307A: Glowbug gamma-ray detection
  88. Fermi GBM Sub-Threshold Detection of GRB 260307B
  89. GRB 260307B: Mephisto optical upper limits
  90. GRB 260307B: possible NOT optical counterpart
  91. GRB 260307B: SVOM/VT upper limit with X band data analysis
  92. Fermi GRB 260307A: Global MASTER-Net observations report
  93. GRB260307B: GROWTH-India Telescope optical upper limit
  94. GRB 260307B: SVOM/VT optical candidate
  95. GRB 260307B: SVOM/C-GFT upper limit
  96. GRB 260307B: SVOM detection of a burst
  97. EP260306a: refined analysis of the EP-WXT and EP-FXT observations
  98. GRB 260207A: TESS Detection and Possible VLA Counterpart
  99. EP260302a: SVOM/VT optical observation
  100. EP260306a: Gemini-North redshift z = 4.773

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