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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"
  1. EP260321a: COLIBRÍ optical upper limit on any supernova shock breakout emission
  2. EP260321a: refined analysis of the EP-WXT and EP-FXT observations, implying a possible supernova shock breakout candidate
  3. EP260321a: SVOM/VT optical upper limit
  4. GRB 260310A: continued optical observation at Mondy
  5. Fermi GBM Sub-Threshold Detection of GRB 260321A
  6. GRB 260321A: SVOM detection of a burst
  7. EP260321a: Kinder observations detect a blue variable star and set limits on a source from the z =0.034 galaxy within the error circle
  8. EP260321a: Global MASTER-Net observations report
  9. EP260321a: Einstein Probe detection of an X-ray transient
  10. GRB 260310A / AT2026fgk: ABObservatory and NOCTIS new optical observations
  11. GRB 260318A: Glowbug gamma-ray detection
  12. GRB 260310A / AT 2026fgk: KAIT optical observations
  13. GRB 260320A: NuSTAR detection of prompt emission
  14. GRB 260310A / AT2026fgk: NuSTAR follow-up detection
  15. EP-WXT trigger 01709258989: KAIT confirmation of a stellar flare
  16. GRB 260310A / AT 2026fgk: FTW optical and NIR observations show no rebrightening
  17. GRB 260310A: no evidence of re-brightening up to 9.6 days in optical observation at Mondy
  18. GRB 260310A / AT 2026fgk: COLIBRÍ evidence of a late rebrightening
  19. GRB 260310A/AT2026fgk: LBT near-infrared observations
  20. NOEMA Detection of GRB 260310A / AT 2026fgk
  21. EP-WXT trigger 01709258989: confirmation of a stellar flare by BOOTES-7
  22. GRB 260318A: SVOM/GRM observation
  23. The EP-WXT trigger 01709258989 is likely a flaring star
  24. GRB 260310A: classification as long GRB based on Eiso, Ep, and T_90
  25. GRB 260318A: GECAM-B observation
  26. GRB260310A/AT2026fgk: Further optical observation from 1.3m DFOT
  27. Fermi GRB 260318A: Global MASTER-Net observations report
  28. GRB 260318A: Fermi GBM Final Real-time Localization
  29. IceCube-260315A: No Candidate Transients from the Zwicky Transient Facility
  30. Fermi Gamma-ray Burst Monitor trigger 795096033/260312500 (GRB 260313A) is unlikely to be a GRB
  31. GRB 260316A / EP260316a: COLIBRÍ optical followup of counterpart candidate
  32. GRB 260310A / AT 2026fgk: radio detection with the VLA
  33. GRB 260310A / AT2026fgk: SVOM/VT optical observations
  34. GRB 260310A / AT2026fgk: LCO optical observations
  35. IceCube-260315A/AT2026fpm: EP-FXT follow-up observation
  36. GRB 260317A: Fermi GBM Final Localization
  37. GRB 260316B: GECAM-B observation
  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. GRB 260316B: AstroSat CZTI detection
  43. EP260316a: refined analysis of the EP-WXT and EP-FXT observations
  44. IceCube-260315A: Upper limits from a search for additional neutrino events in IceCube
  45. EP260316a: Xinglong optical upper limit
  46. GRB 260316B: Fermi GBM Final Real-time Localization
  47. EP260316a: optical upper limit with Kinder observations
  48. EP260316a / GRB 260316A : Fermi-GBM Sub-Threshold Detection
  49. GRB 260314A: Glowbug gamma-ray detection
  50. The EP-WXT trigger 00199258890 (EP260316a): a correction to the trigger time and FXT automatic follow-up
  51. IceCube-260315A: COLIBRÍ optical observations
  52. EP260314a: Xinglong optical upper limit
  53. EP260314a: optical upper limit with Kinder observations
  54. IceCube Alert-260315A/AT2026fpm Automatic MASTER optical blue counterpart candidate
  55. GRB 260310A / AT2026fgk: 1.3m DFOT optical observations
  56. GRB 260310A / AT2026fgk: ABObservatory and NOCTIS optical observations
  57. GRB 260310A / AT 2026fgk: iTelescope optical observations
  58. EP260314a: COLIBRÍ optical upper limit
  59. GRID detection of GRB 260312B
  60. IceCube-260315A - IceCube observation of a high-energy neutrino candidate track-like event
  61. EP260314a: refined analysis of the EP-WXT and EP-FXT observations
  62. EP260314a: BOOTES-6/DPR optical upper limits at early times
  63. EP260314a: Global MASTER-Net observations report
  64. EP260314a: SVOM/VT optical candidate
  65. Fermi trigger No 795185313: Global MASTER-Net observations report
  66. IceCube Alert 260315A: Global MASTER-Net observations report
  67. EP260314a: Einstein Probe detection of an X-ray transient
  68. The EP-WXT trigger 01709258851: Las Cumbres upper limit
  69. GRB 260314A: GECAM-B observation of a burst
  70. Fermi Gamma-ray Burst Monitor trigger 795185313/260314534 is not a GRB
  71. GRB 260310A / AT2026fgk: SAO RAS optical observations
  72. GRB 260310A/AT2026fgk: radio detection at 15GHz
  73. GRB 260310A / AT2026fgk: TNG NIR detection
  74. GRB 260310A / AT2026fgk: OASDG optical observations
  75. GRB 260310A / AT2026fgk: Multiband optical follow-up with Kinder observations
  76. GRB 260310A / AT 2026fgk: COLIBRÍ continuing optical observations
  77. GRB 260310A / AT2026fgk: further CAHA 1.23m telescope optical observations suggest shallow decay
  78. Fermi GRB 260314A: Global MASTER-Net observations report
  79. Fermi GRB 260313A: Global MASTER-Net observations report
  80. GRB 260314A: Fermi GBM Final Real-time Localization
  81. GRB 260310A/AT 2026fgk: WINTER NIR Detections
  82. GRB 260313A: A Correction to the Fermi GBM Final Localization
  83. GRB 260310A: Einstein Probe Follow-up X-ray Telescope (FXT) Detection
  84. GRB 260310A/AT 2026fgk: J-band observations by the SYSU 80 cm infrared telescope
  85. GRB 260310B: Insight-HXMT/HE detection
  86. GRB 260310A/AT 2026fgk: DDOTI Optical Detection
  87. GRB 260310A: NOT optical polarimetry
  88. GRB 260312B: AstroSat CZTI detection
  89. Swift BAT trigger 1500295: A solar flare
  90. GRB 260313A: Fermi GBM Final Real-time Localization
  91. GRB 260310A/AT 2026fgk: Bok spectroscopic observation
  92. Swift BAT trigger 1500287: A solar flare
  93. GRB 260310A / AT2026fgk: OSIRIS+/GTC spectroscopy confirms redshift z = 0.153
  94. GRB 260308A: Insight-HXMT/HE detection
  95. GRB 260307A: CALET Gamma-Ray Burst Monitor detection
  96. GRB 260310A / AT 2026fgk: Location in the Epeak - Eiso diagram
  97. GRB 260310A / AT 2026fgk: COLIBRÍ optical observations
  98. GRB 260310A / AT2026fgk: CAHA 1.23m telescope optical observations
  99. GRB 260310A / AT2026fgk : MASTER OT rebrightening during 7h observations
  100. GRB260310A / AT2026fgk: P200 Spectroscopy

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