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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"

31671 results found.

  1. EP260329a: EP-FXT follow up observation
  2. EP260329a: NOT optical counterpart candidate
  3. EP260329b: Global MASTER-Net observations report
  4. GRB 260327A: Insight-HXMT/HE detection
  5. EP260329b: Optical follow-up with Kinder observations
  6. EP 260329b: COLIBRÍ optical observations
  7. EP260329a: Optical upper limit with Kinder observations
  8. EP260329b: LCO optical observations of the counterpart
  9. GRB 260326A: Insight-HXMT/HE detection
  10. EP260329b: Einstein Probe detection of an X-ray transient
  11. EP-WXT trigger 01709259209: TRT optical counterpart detection
  12. GRID detection of GRB 260326A
  13. GRB 260310A: Gemini-North Spectral Confirmation of Supernova Features
  14. EP260327a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  15. EP260327a: SVOM/VT optical upper limits
  16. SMA Detection of GRB 260310A / AT 2026fgk
  17. GRB 260307B: ATCA Radio Upper Limits
  18. EP260327a: WINTER J-band upper limit
  19. EP260327a: COLIBRÍ optical upper limits
  20. EP260327a: Gemini-North optical upper limits
  21. EP260324a: GROWTH-India Telescope optical observation
  22. EP260327a: Global MASTER-Net observations report
  23. GRB 260310A / AT 2026fgk: COLIBRÍ photometric evidence of the emerging supernova
  24. GRB 260310A: OSIRIS+/GTC spectroscopic detection of the associated BL-Ic, SN 2026fgk
  25. GRB 260310A / AT2026fgk: Late-time infrared detection with MIRAGE on the MDM 1.3m telescope
  26. IPN triangulation of GRB 260320A
  27. GRB 260310A / AT2026fgk: R- and I-band observations with the PKU 60 cm optical telescope
  28. GRB 260326A: Fermi GBM Detection
  29. EP260321a: JinShan near-infrared observations
  30. EP260321a: Upper limits from a neutrino search with IceCube
  31. GRB 260310A/AT2026fgk: Kilonova-Catcher late optical afterglow detection at about 15 days post trigger time
  32. IPN triangulation of GRB 260316B
  33. EP260321a: J-band observations by the SYSU 80 cm infrared telescope
  34. GRID detection of GRB 260320A
  35. EP260321a: Gemini-South confirmation of a supernova (duplicate submission)
  36. EP260321a: Gemini-South confirmation of a supernova
  37. EP260321a: VLT/FORS2 spectroscopy confirmation of an associated type Ic-BL supernova SN 2026gzf
  38. GRB 260310A: LBT optical observations
  39. EP260321A: Mondy optical observations
  40. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limits at the FXT positions
  41. EP-WXT trigger 01709259112: confirmation of a stellar flare by BOOTES-5 & BOOTES-7
  42. GRB 260316B: CALET Gamma-Ray Burst Monitor detection
  43. Fermi GRB 260323A: Global MASTER-Net observations report
  44. GRB260310A: Palomar 60-inch photometry of an extremely bright late-time afterglow with a temporal break at 8 days
  45. GRB 260310A/AT2026fgk: Detection of temporal steepening in Einstein Probe X-ray data
  46. GRB 260320A: Glowbug gamma-ray detection
  47. EP260321a / AT2026gzf: VLT/X-shooter detection of supernova-like spectral features at z = 0.0344
  48. EP260321a: COLIBRÍ further optical observations and brightening
  49. EP260321a: Continued brightening from Kinder follow-up of the emerging supernova candidate
  50. EP260214b: ATCA 6 GHz detection
  51. EP260321a: Early TRT rising followed by JinShan decaying and then re-rising
  52. GRB 260321A: EP-FXT follow-up observation
  53. EP260321a: ZTF and Rubin detections of the candidate optical counterpart to EP260321a
  54. EP260321a: GOTO detection of blue variable source
  55. EP260321a: VLT imaging and spectroscopy show the variable source to be at z = 0.0343
  56. EP260321a: further Kinder optical observations
  57. GRB 260321A: SVOM/VT optical upper limits
  58. EP260321a: Las Cumbres upper limit
  59. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  60. GRB 260320A: Insight-HXMT/HE detection
  61. EP260321a: COLIBRÍ optical upper limit on any supernova shock breakout emission
  62. EP260321a: refined analysis of the EP-WXT and EP-FXT observations, implying a possible supernova shock breakout candidate
  63. EP260321a: SVOM/VT optical upper limit
  64. GRB 260310A: continued optical observation at Mondy
  65. Fermi GBM Sub-Threshold Detection of GRB 260321A
  66. EP260321a: Kinder observations detect a blue variable star and set limits on a source from the z =0.034 galaxy within the error circle
  67. EP260321a: Global MASTER-Net observations report
  68. GRB 260310A / AT2026fgk: ABObservatory and NOCTIS new optical observations
  69. GRB 260318A: Glowbug gamma-ray detection
  70. GRB 260310A / AT 2026fgk: KAIT optical observations
  71. GRB 260320A: NuSTAR detection of prompt emission
  72. GRB 260310A / AT2026fgk: NuSTAR follow-up detection
  73. EP-WXT trigger 01709258989: KAIT confirmation of a stellar flare
  74. GRB 260310A / AT 2026fgk: FTW optical and NIR observations show no rebrightening
  75. GRB 260310A: no evidence of re-brightening up to 9.6 days in optical observation at Mondy
  76. GRB 260310A / AT 2026fgk: COLIBRÍ evidence of a late rebrightening
  77. GRB 260310A/AT2026fgk: LBT near-infrared observations
  78. NOEMA Detection of GRB 260310A / AT 2026fgk
  79. EP-WXT trigger 01709258989: confirmation of a stellar flare by BOOTES-7
  80. GRB 260318A: SVOM/GRM observation
  81. GRB 260310A: classification as long GRB based on Eiso, Ep, and T_90
  82. GRB 260318A: GECAM-B observation
  83. GRB260310A/AT2026fgk: Further optical observation from 1.3m DFOT
  84. Fermi GRB 260318A: Global MASTER-Net observations report
  85. IceCube-260315A: No Candidate Transients from the Zwicky Transient Facility
  86. Fermi Gamma-ray Burst Monitor trigger 795096033/260312500 (GRB 260313A) is unlikely to be a GRB
  87. GRB 260316A / EP260316a: COLIBRÍ optical followup of counterpart candidate
  88. GRB 260310A / AT 2026fgk: radio detection with the VLA
  89. GRB 260310A / AT2026fgk: SVOM/VT optical observations
  90. GRB 260310A / AT2026fgk: LCO optical observations
  91. IceCube-260315A/AT2026fpm: EP-FXT follow-up observation
  92. GRB 260316B: GECAM-B observation
  93. GRB 260316B: SVOM/GRM observation
  94. EP260316a / GRB 260316A: SVOM/VT optical upper limits
  95. EP260316a: COLIBRÍ faint optical counterpart candidate
  96. Fermi-LAT Gamma-ray Observations of IceCube-260315A
  97. GRB 260316B: AstroSat CZTI detection
  98. EP260316a: refined analysis of the EP-WXT and EP-FXT observations
  99. IceCube-260315A: Upper limits from a search for additional neutrino events in IceCube
  100. EP260316a: Xinglong optical upper limit

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