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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. EP260327a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  2. EP260327a: SVOM/VT optical upper limits
  3. SMA Detection of GRB 260310A / AT 2026fgk
  4. GRB 260307B: ATCA Radio Upper Limits
  5. EP260327a: WINTER J-band upper limit
  6. EP260327a: COLIBRÍ optical upper limits
  7. GRB 260327A: AstroSat CZTI detection of a long burst
  8. EP260327a: Gemini-North optical upper limits
  9. EP260324a: GROWTH-India Telescope optical observation
  10. EP260327a: Global MASTER-Net observations report
  11. EP260327a: Einstein Probe detection of an X-ray transient
  12. GRB 260310A / AT 2026fgk: COLIBRÍ photometric evidence of the emerging supernova
  13. GRB 260310A: OSIRIS+/GTC spectroscopic detection of the associated BL-Ic, SN 2026fgk
  14. The EP-WXT trigger 01709259173 is likely a flaring star
  15. GRB 260310A / AT2026fgk: Late-time infrared detection with MIRAGE on the MDM 1.3m telescope
  16. IPN triangulation of GRB 260320A
  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. GRB 260325A: Fermi GBM Final Localization
  22. GRB 260326A: Fermi GBM Final Real-time Localization
  23. EP260321a: Upper limits from a neutrino search with IceCube
  24. Fermi Gamma-ray Burst Monitor trigger 796145512/260325647 is not a GRB
  25. GRB 260310A/AT2026fgk: Kilonova-Catcher late optical afterglow detection at about 15 days post trigger time
  26. IPN triangulation of GRB 260316B
  27. EP260321a: J-band observations by the SYSU 80 cm infrared telescope
  28. GRID detection of GRB 260320A
  29. EP260321a: Gemini-South confirmation of a supernova (duplicate submission)
  30. EP260321a: Gemini-South confirmation of a supernova
  31. Fermi Gamma-ray Burst Monitor trigger 796060650/260324665 is not a GRB
  32. EP260321a: VLT/FORS2 spectroscopy confirmation of an associated type Ic-BL supernova SN 2026gzf
  33. GRB 260310A: LBT optical observations
  34. EP260321A: Mondy optical observations
  35. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limits at the FXT positions
  36. EP-WXT trigger 01709259112: confirmation of a stellar flare by BOOTES-5 & BOOTES-7
  37. GRB 260316B: CALET Gamma-Ray Burst Monitor detection
  38. The EP-WXT trigger 01709259112 is likely a flaring star
  39. Fermi GRB 260323A: Global MASTER-Net observations report
  40. GRB 260323A: Fermi GBM Final Real-time Localization
  41. GRB260310A: Palomar 60-inch photometry of an extremely bright late-time afterglow with a temporal break at 8 days
  42. GRB 260310A/AT2026fgk: Detection of temporal steepening in Einstein Probe X-ray data
  43. GRB 260322A: Fermi GBM Final Localization
  44. GRB 260320A: Glowbug gamma-ray detection
  45. EP260321a / AT2026gzf: VLT/X-shooter detection of supernova-like spectral features at z = 0.0344
  46. EP260321a: COLIBRÍ further optical observations and brightening
  47. Fermi Gamma-ray Burst Monitor trigger 795918973/260323025 is not a GRB
  48. EP260321a: Continued brightening from Kinder follow-up of the emerging supernova candidate
  49. EP260214b: ATCA 6 GHz detection
  50. EP260321a: Early TRT rising followed by JinShan decaying and then re-rising
  51. GRB 260321A: EP-FXT follow-up observation
  52. The EP-WXT trigger 01709259045 is likely a flaring star
  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. GRB 260321A: SVOM detection of a burst
  67. EP260321a: Kinder observations detect a blue variable star and set limits on a source from the z =0.034 galaxy within the error circle
  68. EP260321a: Global MASTER-Net observations report
  69. EP260321a: Einstein Probe detection of an X-ray transient
  70. GRB 260310A / AT2026fgk: ABObservatory and NOCTIS new optical observations
  71. GRB 260318A: Glowbug gamma-ray detection
  72. GRB 260310A / AT 2026fgk: KAIT optical observations
  73. GRB 260320A: NuSTAR detection of prompt emission
  74. GRB 260310A / AT2026fgk: NuSTAR follow-up detection
  75. EP-WXT trigger 01709258989: KAIT confirmation of a stellar flare
  76. GRB 260310A / AT 2026fgk: FTW optical and NIR observations show no rebrightening
  77. GRB 260310A: no evidence of re-brightening up to 9.6 days in optical observation at Mondy
  78. GRB 260310A / AT 2026fgk: COLIBRÍ evidence of a late rebrightening
  79. GRB 260310A/AT2026fgk: LBT near-infrared observations
  80. NOEMA Detection of GRB 260310A / AT 2026fgk
  81. EP-WXT trigger 01709258989: confirmation of a stellar flare by BOOTES-7
  82. GRB 260318A: SVOM/GRM observation
  83. The EP-WXT trigger 01709258989 is likely a flaring star
  84. GRB 260310A: classification as long GRB based on Eiso, Ep, and T_90
  85. GRB 260318A: GECAM-B observation
  86. GRB260310A/AT2026fgk: Further optical observation from 1.3m DFOT
  87. Fermi GRB 260318A: Global MASTER-Net observations report
  88. GRB 260318A: Fermi GBM Final Real-time Localization
  89. IceCube-260315A: No Candidate Transients from the Zwicky Transient Facility
  90. Fermi Gamma-ray Burst Monitor trigger 795096033/260312500 (GRB 260313A) is unlikely to be a GRB
  91. GRB 260316A / EP260316a: COLIBRÍ optical followup of counterpart candidate
  92. GRB 260310A / AT 2026fgk: radio detection with the VLA
  93. GRB 260310A / AT2026fgk: SVOM/VT optical observations
  94. GRB 260310A / AT2026fgk: LCO optical observations
  95. IceCube-260315A/AT2026fpm: EP-FXT follow-up observation
  96. GRB 260317A: Fermi GBM Final Localization
  97. GRB 260316B: GECAM-B observation
  98. GRB 260316B: SVOM/GRM observation
  99. EP260316a / GRB 260316A: SVOM/VT optical upper limits
  100. EP260316a: COLIBRÍ faint optical counterpart candidate

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