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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"

19746 results found.

  1. GRB 260506B: AstroSat CZTI detection
  2. IceCube-260504A: Upper limits from a search for additional neutrino events in IceCube
  3. EP260507a: REM optical/NIR observations
  4. EP260507a: refined analysis of the EP-WXT and EP-FXT observations
  5. GRB 260507B / EP260507a: Fermi-GBM Sub-Threshold Detection
  6. EP260507a: COLIBRÍ optical observations
  7. EP260507a: NOT optical observations
  8. EP260507a: further Liverpool Telescope observations
  9. EP260507a: Liverpool Telescope optical upper limits
  10. EP260507a: TRT optical counterpart detection
  11. EP260507a: Kinder optical counterpart candidate
  12. EP260507a: LCO optical counterpart
  13. EP260507a: Einstein Probe detection of an X-ray transient
  14. GRB 260504B: SVOM/ECLAIRs refined analysis
  15. EP260502a is likely a flaring star
  16. GRB 260503A: GECAM-B observation of a burst
  17. GRB 260421B: radio observation with the VLA
  18. Konus-Wind detection of a burst from SGR 1E1841-045 on 2026 May 2
  19. Fermi-LAT Gamma-ray Observations of IceCube-260504A
  20. GRB 260430B: AstroSat CZTI detection of a long burst
  21. GRB 260502A: SVOM/GRM observation of a short GRB
  22. GRB 260503A: SVOM/GRM observation of a GRB
  23. GRB 260504B: REM optical/NIR observations
  24. GRB 260504B: LCO z-band upper limit
  25. SVOM GRB 260504B: MASTER-OAFA optical observations
  26. GRB 260504B: SVOM detection of a short burst
  27. GRB 260504A: Fermi GBM Final Real-time Localization
  28. SVOM/GRM observation of a bright burst from SGR 1E1841-045
  29. EP260502a: Einstein Probe detection of an X-ray transient
  30. GRB 260429A: SVOM/GRM observation of a short burst
  31. SN 2026kid: Optical follow-up with small-aperture telescopes in Spain and China
  32. EP260430a: refined analysis of the EP-WXT and follow-up EP-FXT observations
  33. GRB 260429B / EP260429a: COLIBRÍ optical upper limit
  34. EP260429a: LCO optical upper limits
  35. EP260430a: LCO optical upper limits
  36. GRB 260430A / EP260430a: COLIBRÍ optical upper limit
  37. EP260430a: Einstein Probe detection of an X-ray transient
  38. EP260429a: EP-WXT detection of a fast X-ray transient
  39. GRB 260428A: SVOM/GRM observation of a possible short burst with extended emission
  40. IceCube-260425A: Upper limits from a search for additional neutrino events in IceCube
  41. GRB 260428A: AstroSat CZTI detection
  42. EP260416a: Mondy and Terskol optical upper limits
  43. GRB 260424B: COLIBRÍ optical upper limit
  44. Fermi-LAT Gamma-ray Observations of IceCube-260425A
  45. EP260321a/SN 2026gzf: spectroscopy at Mondy observatory
  46. GRB 260401A: cubesat Avion detection
  47. EP260321a: Upper limits from ATCA radio observations
  48. GRB 260421B: Kilonova-Catcher optical afterglow detection
  49. EP260416a: Mondy optical observations
  50. GRB 260421B: SVOM/ECLAIRs refined analysis
  51. GRB 260421B: 3.6m DOT optical observation
  52. EP260416a: ZTSh R band observations
  53. IceCube-Cascade 260418A: Upper limits from a search for additional neutrino events in IceCube
  54. GRB 260421B: SVOM/GRM observation
  55. GRB260421B: J band upper limit by SYSU 80cm infrared telescope
  56. GOTO26djh/AT2026jpw: ATCA radio detection
  57. GRB 260421B: J-band upper limit with WINTER
  58. GRB 260421B: LCO optical counterpart detection
  59. GRB 260412A: SVOM/ECLAIRs refined analysis
  60. GRB 260421B: SVOM/VT optical observations
  61. EP260416a: J band upper limit by SYSU 80cm infrared telescope
  62. GRB 260310A: Late-time Chandra X-ray Detection
  63. EP260416a: 1.3m DFOT optical observation
  64. GRB 260421B: VLT/X-shooter spectroscopic redshift z = 2.115
  65. GRB 260421B: LCO optical afterglow confirmation
  66. GRB 260421B: SVOM/COLIBRÍ (FM-GFT) optical detection of a candidate counterpart
  67. GRB 260421B: TRT optical counterpart detection
  68. GRB 260421B: SVOM detection of a long burst
  69. EP260321a: VLA radio follow-up
  70. GRB 260412A: LCOGT Optical Upper Limits
  71. EP260416a: Optical follow-up observations with Kinder
  72. GOTO26djh/AT2026jpw: CrAO and Mondy optical observations of the transient
  73. GRB 260417A: SVOM/GRM observation
  74. EP260321A/AT2026gzf: Optical observation from 1.3m DFOT
  75. EP260417a: GROWTH-India Telescope optical upper limit
  76. EP260417b: GROWTH-India Telescope optical upper limit
  77. EP260416a: Ondrejov D50 optical detection
  78. EP260417a/GRB 260417A: refined analysis of the EP-WXT and follow-up EP-FXT observations
  79. EP260416a: GMG Optical Observation
  80. EP260416a: LCO observations confirm end of flaring phase
  81. EP260324a / AT2026hir: Further multiband optical follow-up with the PKU 60cm Telescope
  82. EP260417a: TRT optical counterpart detection
  83. EP260417a: Einstein Probe detection of an X-ray transient
  84. EP260416a: refined analysis of the EP-WXT and autonomous EP-FXT observations
  85. EP260417b: Einstein Probe detection of a fast X-ray transient
  86. EP260416a: KAIT optical upper limit
  87. EP260416a: COLIBRÍ confirmation of the optical rebrightening
  88. EP260416a: WFST optical observations and rebrightening
  89. GOTO26djh/AT2026jpw: ZTSh R,I bands observations of the transient
  90. GOTO26djh/AT2026jpw: SVOM/VT optical observation
  91. EP260416a: COLIBRÍ optical counterpart candidate
  92. COLIBRI optical observations of the transient GOTO26djh/AT2026jpw
  93. EP260416a: Einstein Probe detection of an X-ray transient
  94. GOTO26djh/AT2026jpw : MASTER OT observation
  95. GOTO26djh/AT2026jpw transient: SAO RAS optical observations
  96. NOT r-band observations of the transient GOTO26djh/AT2026jpw
  97. GOTO discovery of fast-fading transient GOTO26djh/AT2026jpw, a candidate orphan afterglow
  98. EP260409a: Early NIR limits from MIRAGE on the MDM 1.3m telescope
  99. EP260321a: CMO SAI J,K observations
  100. GRB 260412A: Insight-HXMT/HE detection

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