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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"

26999 results found.

  1. Fermi GRB 260323A: Global MASTER-Net observations report
  2. GRB260310A: Palomar 60-inch photometry of an extremely bright late-time afterglow with a temporal break at 8 days
  3. GRB 260320A: Glowbug gamma-ray detection
  4. EP260321a: COLIBRÍ further optical observations and brightening
  5. EP260321a: Continued brightening from Kinder follow-up of the emerging supernova candidate
  6. EP260321a: Early TRT rising followed by JinShan decaying and then re-rising
  7. GRB 260321A: EP-FXT follow-up observation
  8. EP260321a: GOTO detection of blue variable source
  9. EP260321a: VLT imaging and spectroscopy show the variable source to be at z = 0.0343
  10. EP260321a: further Kinder optical observations
  11. GRB 260321A: SVOM/VT optical upper limits
  12. EP260321a: Las Cumbres upper limit
  13. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  14. EP260321a: COLIBRÍ optical upper limit on any supernova shock breakout emission
  15. EP260321a: refined analysis of the EP-WXT and EP-FXT observations, implying a possible supernova shock breakout candidate
  16. EP260321a: SVOM/VT optical upper limit
  17. Fermi GBM Sub-Threshold Detection of GRB 260321A
  18. EP260321a: Kinder observations detect a blue variable star and set limits on a source from the z =0.034 galaxy within the error circle
  19. EP260321a: Global MASTER-Net observations report
  20. EP260321a: Einstein Probe detection of an X-ray transient
  21. GRB 260318A: Glowbug gamma-ray detection
  22. GRB 260310A / AT 2026fgk: KAIT optical observations
  23. GRB 260320A: NuSTAR detection of prompt emission
  24. EP-WXT trigger 01709258989: KAIT confirmation of a stellar flare
  25. GRB 260310A: no evidence of re-brightening up to 9.6 days in optical observation at Mondy
  26. GRB 260310A / AT 2026fgk: COLIBRÍ evidence of a late rebrightening
  27. EP-WXT trigger 01709258989: confirmation of a stellar flare by BOOTES-7
  28. GRB 260318A: SVOM/GRM observation
  29. GRB 260310A: classification as long GRB based on Eiso, Ep, and T_90
  30. GRB260310A/AT2026fgk: Further optical observation from 1.3m DFOT
  31. Fermi GRB 260318A: Global MASTER-Net observations report
  32. GRB 260316A / EP260316a: COLIBRÍ optical followup of counterpart candidate
  33. GRB 260310A / AT 2026fgk: radio detection with the VLA
  34. GRB 260310A / AT2026fgk: SVOM/VT optical observations
  35. GRB 260310A / AT2026fgk: LCO optical observations
  36. GRB 260316B: SVOM/GRM observation
  37. EP260316a / GRB 260316A: SVOM/VT optical upper limits
  38. EP260316a: COLIBRÍ faint optical counterpart candidate
  39. Fermi-LAT Gamma-ray Observations of IceCube-260315A
  40. EP260316a: refined analysis of the EP-WXT and EP-FXT observations
  41. IceCube-260315A: Upper limits from a search for additional neutrino events in IceCube
  42. EP260316a: Xinglong optical upper limit
  43. EP260316a: optical upper limit with Kinder observations
  44. EP260316a / GRB 260316A : Fermi-GBM Sub-Threshold Detection
  45. GRB 260314A: Glowbug gamma-ray detection
  46. The EP-WXT trigger 00199258890 (EP260316a): a correction to the trigger time and FXT automatic follow-up
  47. IceCube-260315A: COLIBRÍ optical observations
  48. EP260314a: Xinglong optical upper limit
  49. EP260314a: optical upper limit with Kinder observations
  50. IceCube Alert-260315A/AT2026fpm Automatic MASTER optical blue counterpart candidate
  51. GRB 260310A / AT2026fgk: 1.3m DFOT optical observations
  52. GRB 260310A / AT 2026fgk: iTelescope optical observations
  53. EP260314a: COLIBRÍ optical upper limit
  54. EP260314a: refined analysis of the EP-WXT and EP-FXT observations
  55. EP260314a: Global MASTER-Net observations report
  56. EP260314a: SVOM/VT optical candidate
  57. Fermi trigger No 795185313: Global MASTER-Net observations report
  58. IceCube Alert 260315A: Global MASTER-Net observations report
  59. EP260314a: Einstein Probe detection of an X-ray transient
  60. GRB 260310A / AT2026fgk: SAO RAS optical observations
  61. GRB 260310A / AT2026fgk: Multiband optical follow-up with Kinder observations
  62. GRB 260310A / AT 2026fgk: COLIBRÍ continuing optical observations
  63. Fermi GRB 260314A: Global MASTER-Net observations report
  64. Fermi GRB 260313A: Global MASTER-Net observations report
  65. GRB 260310A/AT 2026fgk: WINTER NIR Detections
  66. GRB 260310A/AT 2026fgk: J-band observations by the SYSU 80 cm infrared telescope
  67. GRB 260310A/AT 2026fgk: DDOTI Optical Detection
  68. GRB 260312B: AstroSat CZTI detection
  69. GRB 260310A / AT2026fgk: OSIRIS+/GTC spectroscopy confirms redshift z = 0.153
  70. GRB 260310A / AT 2026fgk: COLIBRÍ optical observations
  71. GRB 260310A / AT2026fgk : MASTER OT rebrightening during 7h observations
  72. GRB 260312B: Glowbug gamma-ray detection
  73. GRB 260310A: Fermi GBM Observation
  74. GRB 260310A: potential optical counterpart
  75. Fermi GRB 260312B: Global MASTER-Net observations report
  76. Fermi GRB 260311B: Global MASTER-Net observations report
  77. GRB 260312B: BALROG localization (Fermi Trigger 795001611 / GRB 260312407)
  78. GRB 260131A/B: radio detection with the VLA
  79. EP260302a: MeerKAT radio counterpart
  80. GRB 260308A: SVOM/GRM observation of a short GRB
  81. EP260306a: Mondy optical upper limit
  82. Fermi GRB 260310B: Global MASTER-Net observations report
  83. Fermi GRB 260310A: Global MASTER-Net observations report
  84. GRB 260208A: radio detection with the VLA
  85. GRB 260307A: Glowbug gamma-ray detection
  86. Fermi GBM Sub-Threshold Detection of GRB 260307B
  87. GRB 260307B: Mephisto optical upper limits
  88. GRB 260307B: possible NOT optical counterpart
  89. GRB 260307B: SVOM/VT upper limit with X band data analysis
  90. Fermi GRB 260307A: Global MASTER-Net observations report
  91. GRB260307B: GROWTH-India Telescope optical upper limit
  92. GRB 260307B: SVOM/VT optical candidate
  93. GRB 260307B: SVOM/C-GFT upper limit
  94. GRB 260307B: SVOM detection of a burst
  95. EP260306a: refined analysis of the EP-WXT and EP-FXT observations
  96. GRB 260207A: TESS Detection and Possible VLA Counterpart
  97. EP260302a: SVOM/VT optical observation
  98. EP260306a: Gemini-North redshift z = 4.773
  99. EP260306a: SVOM/VT optical observation
  100. EP260302a: Gemini-South redshift z = 1.535

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