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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"

26179 results found.

  1. GRB 260316B: CALET Gamma-Ray Burst Monitor detection
  2. The EP-WXT trigger 01709259112 is likely a flaring star
  3. Fermi GRB 260323A: Global MASTER-Net observations report
  4. GRB 260323A: Fermi GBM Final Real-time Localization
  5. GRB 260310A/AT2026fgk: Detection of temporal steepening in Einstein Probe X-ray data
  6. GRB 260322A: Fermi GBM Final Localization
  7. EP260321a / AT2026gzf: VLT/X-shooter detection of supernova-like spectral features at z = 0.0344
  8. EP260321a: COLIBRÍ further optical observations and brightening
  9. Fermi Gamma-ray Burst Monitor trigger 795918973/260323025 is not a GRB
  10. EP260321a: Continued brightening from Kinder follow-up of the emerging supernova candidate
  11. EP260214b: ATCA 6 GHz detection
  12. EP260321a: Early TRT rising followed by JinShan decaying and then re-rising
  13. GRB 260321A: EP-FXT follow-up observation
  14. The EP-WXT trigger 01709259045 is likely a flaring star
  15. EP260321a: ZTF and Rubin detections of the candidate optical counterpart to EP260321a
  16. EP260321a: GOTO detection of blue variable source
  17. EP260321a: VLT imaging and spectroscopy show the variable source to be at z = 0.0343
  18. EP260321a: further Kinder optical observations
  19. GRB 260321A: SVOM/VT optical upper limits
  20. EP260321a: Las Cumbres upper limit
  21. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  22. EP260321a: COLIBRÍ optical upper limit on any supernova shock breakout emission
  23. EP260321a: refined analysis of the EP-WXT and EP-FXT observations, implying a possible supernova shock breakout candidate
  24. EP260321a: SVOM/VT optical upper limit
  25. Fermi GBM Sub-Threshold Detection of GRB 260321A
  26. GRB 260321A: SVOM detection of a burst
  27. EP260321a: Kinder observations detect a blue variable star and set limits on a source from the z =0.034 galaxy within the error circle
  28. EP260321a: Global MASTER-Net observations report
  29. EP260321a: Einstein Probe detection of an X-ray transient
  30. EP-WXT trigger 01709258989: KAIT confirmation of a stellar flare
  31. GRB 260310A / AT 2026fgk: FTW optical and NIR observations show no rebrightening
  32. GRB 260310A / AT 2026fgk: COLIBRÍ evidence of a late rebrightening
  33. GRB 260310A/AT2026fgk: LBT near-infrared observations
  34. EP-WXT trigger 01709258989: confirmation of a stellar flare by BOOTES-7
  35. GRB 260318A: SVOM/GRM observation
  36. The EP-WXT trigger 01709258989 is likely a flaring star
  37. GRB 260310A: classification as long GRB based on Eiso, Ep, and T_90
  38. GRB 260318A: GECAM-B observation
  39. GRB260310A/AT2026fgk: Further optical observation from 1.3m DFOT
  40. Fermi GRB 260318A: Global MASTER-Net observations report
  41. GRB 260318A: Fermi GBM Final Real-time Localization
  42. Fermi Gamma-ray Burst Monitor trigger 795096033/260312500 (GRB 260313A) is unlikely to be a GRB
  43. GRB 260316A / EP260316a: COLIBRÍ optical followup of counterpart candidate
  44. GRB 260310A / AT2026fgk: SVOM/VT optical observations
  45. GRB 260310A / AT2026fgk: LCO optical observations
  46. IceCube-260315A/AT2026fpm: EP-FXT follow-up observation
  47. GRB 260317A: Fermi GBM Final Localization
  48. GRB 260316B: GECAM-B observation
  49. GRB 260316B: SVOM/GRM observation
  50. EP260316a / GRB 260316A: SVOM/VT optical upper limits
  51. EP260316a: COLIBRÍ faint optical counterpart candidate
  52. GRB 260316B: AstroSat CZTI detection
  53. EP260316a: refined analysis of the EP-WXT and EP-FXT observations
  54. EP260316a: Xinglong optical upper limit
  55. GRB 260316B: Fermi GBM Final Real-time Localization
  56. EP260316a / GRB 260316A : Fermi-GBM Sub-Threshold Detection
  57. The EP-WXT trigger 00199258890 (EP260316a): a correction to the trigger time and FXT automatic follow-up
  58. IceCube-260315A: COLIBRÍ optical observations
  59. EP260314a: Xinglong optical upper limit
  60. IceCube Alert-260315A/AT2026fpm Automatic MASTER optical blue counterpart candidate
  61. GRB 260310A / AT2026fgk: 1.3m DFOT optical observations
  62. GRB 260310A / AT2026fgk: ABObservatory and NOCTIS optical observations
  63. GRB 260310A / AT 2026fgk: iTelescope optical observations
  64. EP260314a: COLIBRÍ optical upper limit
  65. GRID detection of GRB 260312B
  66. EP260314a: refined analysis of the EP-WXT and EP-FXT observations
  67. EP260314a: BOOTES-6/DPR optical upper limits at early times
  68. EP260314a: Global MASTER-Net observations report
  69. EP260314a: SVOM/VT optical candidate
  70. Fermi trigger No 795185313: Global MASTER-Net observations report
  71. IceCube Alert 260315A: Global MASTER-Net observations report
  72. EP260314a: Einstein Probe detection of an X-ray transient
  73. The EP-WXT trigger 01709258851: Las Cumbres upper limit
  74. GRB 260314A: GECAM-B observation of a burst
  75. Fermi Gamma-ray Burst Monitor trigger 795185313/260314534 is not a GRB
  76. GRB 260310A / AT2026fgk: SAO RAS optical observations
  77. GRB 260310A / AT2026fgk: TNG NIR detection
  78. GRB 260310A / AT2026fgk: OASDG optical observations
  79. GRB 260310A / AT 2026fgk: COLIBRÍ continuing optical observations
  80. GRB 260310A / AT2026fgk: further CAHA 1.23m telescope optical observations suggest shallow decay
  81. Fermi GRB 260314A: Global MASTER-Net observations report
  82. Fermi GRB 260313A: Global MASTER-Net observations report
  83. GRB 260314A: Fermi GBM Final Real-time Localization
  84. GRB 260310A/AT 2026fgk: WINTER NIR Detections
  85. GRB 260313A: A Correction to the Fermi GBM Final Localization
  86. GRB 260310A/AT 2026fgk: J-band observations by the SYSU 80 cm infrared telescope
  87. GRB 260310A/AT 2026fgk: DDOTI Optical Detection
  88. GRB 260310A: NOT optical polarimetry
  89. Swift BAT trigger 1500295: A solar flare
  90. GRB 260313A: Fermi GBM Final Real-time Localization
  91. Swift BAT trigger 1500287: A solar flare
  92. GRB 260310A / AT2026fgk: OSIRIS+/GTC spectroscopy confirms redshift z = 0.153
  93. GRB 260307A: CALET Gamma-Ray Burst Monitor detection
  94. GRB 260310A / AT 2026fgk: COLIBRÍ optical observations
  95. GRB 260310A / AT2026fgk: CAHA 1.23m telescope optical observations
  96. GRB260310A / AT2026fgk: P200 Spectroscopy
  97. GRB 260310A: Fermi GBM Observation
  98. Fermi GRB 260312B: Global MASTER-Net observations report
  99. Fermi GRB 260311B: Global MASTER-Net observations report
  100. Swift BAT trigger 1500148: A solar flare

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