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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. GRB 260310A: OSIRIS+/GTC spectroscopic detection of the associated BL-Ic, SN 2026fgk
  2. The EP-WXT trigger 01709259173 is likely a flaring star
  3. GRB 260310A / AT2026fgk: Late-time infrared detection with MIRAGE on the MDM 1.3m telescope
  4. IPN triangulation of GRB 260320A
  5. EP260324a: ZTF discovery of the optical counterpart ZTF26aapviim/AT2026hir
  6. GRB 260310A / AT2026fgk: R- and I-band observations with the PKU 60 cm optical telescope
  7. GRB 260326A: Fermi GBM Detection
  8. EP260321a: JinShan near-infrared observations
  9. GRB 260325A: Fermi GBM Final Localization
  10. GRB 260326A: Fermi GBM Final Real-time Localization
  11. EP260321a: Upper limits from a neutrino search with IceCube
  12. Fermi Gamma-ray Burst Monitor trigger 796145512/260325647 is not a GRB
  13. GRB 260310A/AT2026fgk: Kilonova-Catcher late optical afterglow detection at about 15 days post trigger time
  14. IPN triangulation of GRB 260316B
  15. EP260321a: J-band observations by the SYSU 80 cm infrared telescope
  16. GRID detection of GRB 260320A
  17. EP260321a: Gemini-South confirmation of a supernova (duplicate submission)
  18. EP260321a: Gemini-South confirmation of a supernova
  19. Fermi Gamma-ray Burst Monitor trigger 796060650/260324665 is not a GRB
  20. EP260321a: VLT/FORS2 spectroscopy confirmation of an associated type Ic-BL supernova SN 2026gzf
  21. GRB 260310A: LBT optical observations
  22. EP260321A: Mondy optical observations
  23. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limits at the FXT positions
  24. EP-WXT trigger 01709259112: confirmation of a stellar flare by BOOTES-5 & BOOTES-7
  25. GRB 260316B: CALET Gamma-Ray Burst Monitor detection
  26. The EP-WXT trigger 01709259112 is likely a flaring star
  27. Fermi GRB 260323A: Global MASTER-Net observations report
  28. GRB 260323A: Fermi GBM Final Real-time Localization
  29. GRB260310A: Palomar 60-inch photometry of an extremely bright late-time afterglow with a temporal break at 8 days
  30. GRB 260310A/AT2026fgk: Detection of temporal steepening in Einstein Probe X-ray data
  31. GRB 260322A: Fermi GBM Final Localization
  32. GRB 260320A: Glowbug gamma-ray detection
  33. EP260321a / AT2026gzf: VLT/X-shooter detection of supernova-like spectral features at z = 0.0344
  34. EP260321a: COLIBRÍ further optical observations and brightening
  35. Fermi Gamma-ray Burst Monitor trigger 795918973/260323025 is not a GRB
  36. EP260321a: Continued brightening from Kinder follow-up of the emerging supernova candidate
  37. EP260214b: ATCA 6 GHz detection
  38. EP260321a: Early TRT rising followed by JinShan decaying and then re-rising
  39. GRB 260321A: EP-FXT follow-up observation
  40. The EP-WXT trigger 01709259045 is likely a flaring star
  41. EP260321a: ZTF and Rubin detections of the candidate optical counterpart to EP260321a
  42. EP260321a: GOTO detection of blue variable source
  43. EP260321a: VLT imaging and spectroscopy show the variable source to be at z = 0.0343
  44. EP260321a: further Kinder optical observations
  45. GRB 260321A: SVOM/VT optical upper limits
  46. EP260321a: Las Cumbres upper limit
  47. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  48. GRB 260320A: Insight-HXMT/HE detection
  49. EP260321a: COLIBRÍ optical upper limit on any supernova shock breakout emission
  50. EP260321a: refined analysis of the EP-WXT and EP-FXT observations, implying a possible supernova shock breakout candidate
  51. EP260321a: SVOM/VT optical upper limit
  52. GRB 260310A: continued optical observation at Mondy
  53. Fermi GBM Sub-Threshold Detection of GRB 260321A
  54. GRB 260321A: SVOM detection of a burst
  55. EP260321a: Kinder observations detect a blue variable star and set limits on a source from the z =0.034 galaxy within the error circle
  56. EP260321a: Global MASTER-Net observations report
  57. EP260321a: Einstein Probe detection of an X-ray transient
  58. GRB 260310A / AT2026fgk: ABObservatory and NOCTIS new optical observations
  59. GRB 260318A: Glowbug gamma-ray detection
  60. GRB 260310A / AT 2026fgk: KAIT optical observations
  61. GRB 260320A: NuSTAR detection of prompt emission
  62. GRB 260310A / AT2026fgk: NuSTAR follow-up detection
  63. EP-WXT trigger 01709258989: KAIT confirmation of a stellar flare
  64. GRB 260310A / AT 2026fgk: FTW optical and NIR observations show no rebrightening
  65. GRB 260310A: no evidence of re-brightening up to 9.6 days in optical observation at Mondy
  66. GRB 260310A / AT 2026fgk: COLIBRÍ evidence of a late rebrightening
  67. GRB 260310A/AT2026fgk: LBT near-infrared observations
  68. NOEMA Detection of GRB 260310A / AT 2026fgk
  69. EP-WXT trigger 01709258989: confirmation of a stellar flare by BOOTES-7
  70. GRB 260318A: SVOM/GRM observation
  71. The EP-WXT trigger 01709258989 is likely a flaring star
  72. GRB 260310A: classification as long GRB based on Eiso, Ep, and T_90
  73. GRB 260318A: GECAM-B observation
  74. GRB260310A/AT2026fgk: Further optical observation from 1.3m DFOT
  75. Fermi GRB 260318A: Global MASTER-Net observations report
  76. GRB 260318A: Fermi GBM Final Real-time Localization
  77. IceCube-260315A: No Candidate Transients from the Zwicky Transient Facility
  78. Fermi Gamma-ray Burst Monitor trigger 795096033/260312500 (GRB 260313A) is unlikely to be a GRB
  79. GRB 260316A / EP260316a: COLIBRÍ optical followup of counterpart candidate
  80. GRB 260310A / AT 2026fgk: radio detection with the VLA
  81. GRB 260310A / AT2026fgk: SVOM/VT optical observations
  82. GRB 260310A / AT2026fgk: LCO optical observations
  83. IceCube-260315A/AT2026fpm: EP-FXT follow-up observation
  84. GRB 260317A: Fermi GBM Final Localization
  85. GRB 260316B: GECAM-B observation
  86. GRB 260316B: SVOM/GRM observation
  87. EP260316a / GRB 260316A: SVOM/VT optical upper limits
  88. EP260316a: COLIBRÍ faint optical counterpart candidate
  89. Fermi-LAT Gamma-ray Observations of IceCube-260315A
  90. GRB 260316B: AstroSat CZTI detection
  91. EP260316a: refined analysis of the EP-WXT and EP-FXT observations
  92. IceCube-260315A: Upper limits from a search for additional neutrino events in IceCube
  93. EP260316a: Xinglong optical upper limit
  94. GRB 260316B: Fermi GBM Final Real-time Localization
  95. EP260316a: optical upper limit with Kinder observations
  96. EP260316a / GRB 260316A : Fermi-GBM Sub-Threshold Detection
  97. GRB 260314A: Glowbug gamma-ray detection
  98. The EP-WXT trigger 00199258890 (EP260316a): a correction to the trigger time and FXT automatic follow-up
  99. IceCube-260315A: COLIBRÍ optical observations
  100. EP260314a: Xinglong optical upper limit

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