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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. EP260329a: Optical upper limit with Kinder observations
  2. EP260329b: LCO optical observations of the counterpart
  3. EP260329b: Einstein Probe detection of an X-ray transient
  4. EP260329a: Einstein Probe detection of an X-ray transient
  5. EP-WXT trigger 01709259209: TRT optical counterpart detection
  6. GRID detection of GRB 260326A
  7. GRB 260310A: Gemini-North Spectral Confirmation of Supernova Features
  8. EP260327a: SVOM/VT optical upper limits
  9. SMA Detection of GRB 260310A / AT 2026fgk
  10. EP260327a: WINTER J-band upper limit
  11. EP260327a: COLIBRÍ optical upper limits
  12. GRB 260327A: AstroSat CZTI detection of a long burst
  13. EP260327a: Gemini-North optical upper limits
  14. EP260324a: GROWTH-India Telescope optical observation
  15. EP260327a: Global MASTER-Net observations report
  16. GRB 260310A: OSIRIS+/GTC spectroscopic detection of the associated BL-Ic, SN 2026fgk
  17. GRB 260310A / AT2026fgk: Late-time infrared detection with MIRAGE on the MDM 1.3m telescope
  18. IPN triangulation of GRB 260320A
  19. EP260324a: ZTF discovery of the optical counterpart ZTF26aapviim/AT2026hir
  20. GRB 260310A / AT2026fgk: R- and I-band observations with the PKU 60 cm optical telescope
  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. GRID detection of GRB 260320A
  27. EP260321a: Gemini-South confirmation of a supernova (duplicate submission)
  28. EP260321a: Gemini-South confirmation of a supernova
  29. Fermi Gamma-ray Burst Monitor trigger 796060650/260324665 is not a GRB
  30. EP260321A: Mondy optical observations
  31. EP-WXT trigger 01709259112: confirmation of a stellar flare by BOOTES-5 & BOOTES-7
  32. GRB 260316B: CALET Gamma-Ray Burst Monitor detection
  33. Fermi GRB 260323A: Global MASTER-Net observations report
  34. GRB 260323A: Fermi GBM Final Real-time Localization
  35. GRB260310A: Palomar 60-inch photometry of an extremely bright late-time afterglow with a temporal break at 8 days
  36. GRB 260310A/AT2026fgk: Detection of temporal steepening in Einstein Probe X-ray data
  37. GRB 260322A: Fermi GBM Final Localization
  38. GRB 260320A: Glowbug gamma-ray detection
  39. Fermi Gamma-ray Burst Monitor trigger 795918973/260323025 is not a GRB
  40. EP260321a: Continued brightening from Kinder follow-up of the emerging supernova candidate
  41. EP260214b: ATCA 6 GHz detection
  42. GRB 260321A: EP-FXT follow-up observation
  43. The EP-WXT trigger 01709259045 is likely a flaring star
  44. EP260321a: ZTF and Rubin detections of the candidate optical counterpart to EP260321a
  45. EP260321a: VLT imaging and spectroscopy show the variable source to be at z = 0.0343
  46. EP260321a: further Kinder optical observations
  47. EP260321a: Las Cumbres upper limit
  48. GRB 260321A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  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. GRB 260310A: continued optical observation at Mondy
  52. Fermi GBM Sub-Threshold Detection of GRB 260321A
  53. GRB 260321A: SVOM detection of a burst
  54. EP260321a: Einstein Probe detection of an X-ray transient
  55. GRB 260310A / AT2026fgk: ABObservatory and NOCTIS new optical observations
  56. GRB 260310A / AT 2026fgk: KAIT optical observations
  57. GRB 260310A / AT2026fgk: NuSTAR follow-up detection
  58. GRB 260310A / AT 2026fgk: FTW optical and NIR observations show no rebrightening
  59. GRB 260310A: no evidence of re-brightening up to 9.6 days in optical observation at Mondy
  60. GRB 260310A / AT 2026fgk: COLIBRÍ evidence of a late rebrightening
  61. GRB 260318A: SVOM/GRM observation
  62. GRB 260310A: classification as long GRB based on Eiso, Ep, and T_90
  63. GRB260310A/AT2026fgk: Further optical observation from 1.3m DFOT
  64. Fermi GRB 260318A: Global MASTER-Net observations report
  65. IceCube-260315A: No Candidate Transients from the Zwicky Transient Facility
  66. Fermi Gamma-ray Burst Monitor trigger 795096033/260312500 (GRB 260313A) is unlikely to be a GRB
  67. GRB 260316A / EP260316a: COLIBRÍ optical followup of counterpart candidate
  68. GRB 260310A / AT2026fgk: SVOM/VT optical observations
  69. GRB 260310A / AT2026fgk: LCO optical observations
  70. IceCube-260315A/AT2026fpm: EP-FXT follow-up observation
  71. GRB 260317A: Fermi GBM Final Localization
  72. GRB 260316B: GECAM-B observation
  73. GRB 260316B: SVOM/GRM observation
  74. EP260316a: COLIBRÍ faint optical counterpart candidate
  75. Fermi-LAT Gamma-ray Observations of IceCube-260315A
  76. EP260316a: refined analysis of the EP-WXT and EP-FXT observations
  77. EP260316a: Xinglong optical upper limit
  78. GRB 260316B: Fermi GBM Final Real-time Localization
  79. EP260316a: optical upper limit with Kinder observations
  80. EP260316a / GRB 260316A : Fermi-GBM Sub-Threshold Detection
  81. GRB 260314A: Glowbug gamma-ray detection
  82. IceCube-260315A: COLIBRÍ optical observations
  83. EP260314a: Xinglong optical upper limit
  84. EP260314a: optical upper limit with Kinder observations
  85. GRB 260310A / AT2026fgk: ABObservatory and NOCTIS optical observations
  86. GRB 260310A / AT 2026fgk: iTelescope optical observations
  87. EP260314a: BOOTES-6/DPR optical upper limits at early times
  88. EP260314a: Global MASTER-Net observations report
  89. EP260314a: SVOM/VT optical candidate
  90. GRB 260314A: GECAM-B observation of a burst
  91. GRB 260310A / AT2026fgk: SAO RAS optical observations
  92. GRB 260310A/AT2026fgk: radio detection at 15GHz
  93. GRB 260310A / AT2026fgk: further CAHA 1.23m telescope optical observations suggest shallow decay
  94. Fermi GRB 260313A: Global MASTER-Net observations report
  95. GRB 260310A/AT 2026fgk: WINTER NIR Detections
  96. GRB 260310A/AT 2026fgk: DDOTI Optical Detection
  97. Swift BAT trigger 1500287: A solar flare
  98. GRB 260310A / AT2026fgk: OSIRIS+/GTC spectroscopy confirms redshift z = 0.153
  99. GRB 260307A: CALET Gamma-Ray Burst Monitor detection
  100. GRB 260310A / AT2026fgk : MASTER OT rebrightening during 7h observations

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