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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"

27324 results found.

  1. EP260329b: LCO optical observations of the counterpart
  2. GRB 260326A: Insight-HXMT/HE detection
  3. EP260329b: Einstein Probe detection of an X-ray transient
  4. EP260329a: Einstein Probe detection of an X-ray transient
  5. EP-WXT trigger 01709259209: TRT optical counterpart detection
  6. The EP-WXT trigger 01709259209 (EP260329b?): Las Cumbres discovery of the optical counterpart
  7. EP260327a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  8. EP260327a: SVOM/VT optical upper limits
  9. EP260327a: WINTER J-band upper limit
  10. EP260327a: COLIBRÍ optical upper limits
  11. EP260327a: Gemini-North optical upper limits
  12. EP260324a: GROWTH-India Telescope optical observation
  13. EP260327a: Global MASTER-Net observations report
  14. EP260327a: Einstein Probe detection of an X-ray transient
  15. GRB 260310A / AT 2026fgk: COLIBRÍ photometric evidence of the emerging supernova
  16. GRB 260310A / AT2026fgk: Late-time infrared detection with MIRAGE on the MDM 1.3m telescope
  17. EP260324a: ZTF discovery of the optical counterpart ZTF26aapviim/AT2026hir
  18. GRB 260310A / AT2026fgk: R- and I-band observations with the PKU 60 cm optical telescope
  19. GRB 260326A: Fermi GBM Detection
  20. EP260321a: JinShan near-infrared observations
  21. EP260321a: Upper limits from a neutrino search with IceCube
  22. GRB 260310A/AT2026fgk: Kilonova-Catcher late optical afterglow detection at about 15 days post trigger time
  23. EP260321a: J-band observations by the SYSU 80 cm infrared telescope
  24. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limits at the FXT positions
  25. EP-WXT trigger 01709259112: confirmation of a stellar flare by BOOTES-5 & BOOTES-7
  26. Fermi GRB 260323A: Global MASTER-Net observations report
  27. GRB260310A: Palomar 60-inch photometry of an extremely bright late-time afterglow with a temporal break at 8 days
  28. GRB 260320A: Glowbug gamma-ray detection
  29. EP260321a: COLIBRÍ further optical observations and brightening
  30. EP260321a: Continued brightening from Kinder follow-up of the emerging supernova candidate
  31. EP260321a: Early TRT rising followed by JinShan decaying and then re-rising
  32. GRB 260321A: EP-FXT follow-up observation
  33. EP260321a: GOTO detection of blue variable source
  34. EP260321a: VLT imaging and spectroscopy show the variable source to be at z = 0.0343
  35. EP260321a: further Kinder optical observations
  36. GRB 260321A: SVOM/VT optical upper limits
  37. EP260321a: Las Cumbres upper limit
  38. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  39. EP260321a: COLIBRÍ optical upper limit on any supernova shock breakout emission
  40. EP260321a: refined analysis of the EP-WXT and EP-FXT observations, implying a possible supernova shock breakout candidate
  41. EP260321a: SVOM/VT optical upper limit
  42. Fermi GBM Sub-Threshold Detection of GRB 260321A
  43. EP260321a: Kinder observations detect a blue variable star and set limits on a source from the z =0.034 galaxy within the error circle
  44. EP260321a: Global MASTER-Net observations report
  45. EP260321a: Einstein Probe detection of an X-ray transient
  46. GRB 260318A: Glowbug gamma-ray detection
  47. GRB 260310A / AT 2026fgk: KAIT optical observations
  48. GRB 260320A: NuSTAR detection of prompt emission
  49. EP-WXT trigger 01709258989: KAIT confirmation of a stellar flare
  50. GRB 260310A: no evidence of re-brightening up to 9.6 days in optical observation at Mondy
  51. GRB 260310A / AT 2026fgk: COLIBRÍ evidence of a late rebrightening
  52. EP-WXT trigger 01709258989: confirmation of a stellar flare by BOOTES-7
  53. GRB 260318A: SVOM/GRM observation
  54. GRB 260310A: classification as long GRB based on Eiso, Ep, and T_90
  55. GRB260310A/AT2026fgk: Further optical observation from 1.3m DFOT
  56. Fermi GRB 260318A: Global MASTER-Net observations report
  57. GRB 260316A / EP260316a: COLIBRÍ optical followup of counterpart candidate
  58. GRB 260310A / AT 2026fgk: radio detection with the VLA
  59. GRB 260310A / AT2026fgk: SVOM/VT optical observations
  60. GRB 260310A / AT2026fgk: LCO optical observations
  61. GRB 260316B: SVOM/GRM observation
  62. EP260316a / GRB 260316A: SVOM/VT optical upper limits
  63. EP260316a: COLIBRÍ faint optical counterpart candidate
  64. Fermi-LAT Gamma-ray Observations of IceCube-260315A
  65. EP260316a: refined analysis of the EP-WXT and EP-FXT observations
  66. IceCube-260315A: Upper limits from a search for additional neutrino events in IceCube
  67. EP260316a: Xinglong optical upper limit
  68. EP260316a: optical upper limit with Kinder observations
  69. EP260316a / GRB 260316A : Fermi-GBM Sub-Threshold Detection
  70. GRB 260314A: Glowbug gamma-ray detection
  71. The EP-WXT trigger 00199258890 (EP260316a): a correction to the trigger time and FXT automatic follow-up
  72. IceCube-260315A: COLIBRÍ optical observations
  73. EP260314a: Xinglong optical upper limit
  74. EP260314a: optical upper limit with Kinder observations
  75. IceCube Alert-260315A/AT2026fpm Automatic MASTER optical blue counterpart candidate
  76. GRB 260310A / AT2026fgk: 1.3m DFOT optical observations
  77. GRB 260310A / AT 2026fgk: iTelescope optical observations
  78. EP260314a: COLIBRÍ optical upper limit
  79. EP260314a: refined analysis of the EP-WXT and EP-FXT observations
  80. EP260314a: Global MASTER-Net observations report
  81. EP260314a: SVOM/VT optical candidate
  82. Fermi trigger No 795185313: Global MASTER-Net observations report
  83. IceCube Alert 260315A: Global MASTER-Net observations report
  84. EP260314a: Einstein Probe detection of an X-ray transient
  85. GRB 260310A / AT2026fgk: SAO RAS optical observations
  86. GRB 260310A / AT2026fgk: Multiband optical follow-up with Kinder observations
  87. GRB 260310A / AT 2026fgk: COLIBRÍ continuing optical observations
  88. Fermi GRB 260314A: Global MASTER-Net observations report
  89. Fermi GRB 260313A: Global MASTER-Net observations report
  90. GRB 260310A/AT 2026fgk: WINTER NIR Detections
  91. GRB 260310A/AT 2026fgk: J-band observations by the SYSU 80 cm infrared telescope
  92. GRB 260310A/AT 2026fgk: DDOTI Optical Detection
  93. GRB 260312B: AstroSat CZTI detection
  94. GRB 260310A / AT2026fgk: OSIRIS+/GTC spectroscopy confirms redshift z = 0.153
  95. GRB 260310A / AT 2026fgk: COLIBRÍ optical observations
  96. GRB 260310A / AT2026fgk : MASTER OT rebrightening during 7h observations
  97. GRB 260312B: Glowbug gamma-ray detection
  98. GRB 260310A: Fermi GBM Observation
  99. GRB 260310A: potential optical counterpart
  100. Fermi GRB 260312B: Global MASTER-Net observations report

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