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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. EP-WXT trigger 01709258652: 50cm Telescope multi-band observations
  2. EP260227a: further LCO observations
  3. EP260227a: SVOM/VT optical observation
  4. GRB 260228A: SVOM/VT optical upper limits
  5. GRB 260225D: SVOM/GRM observation
  6. EP260227A: 3.6m DOT optical afterglow detection
  7. GRB 260225B: SVOM/GRM observation
  8. GRB 260228A: SVOM detection of a burst
  9. EP260227a: FTW optical and NIR observations
  10. EP260227a: Liverpool Telescope optical observations
  11. EP260227a: LCOGT Optical Observations
  12. GRB 260226A: Asiago r-band upper limit
  13. EP260227a: Thai National Telescope observations
  14. EP260227a: likely GTC/OSIRIS+ redshift z = 2.714
  15. EP260227a: Liverpool Telescope observations
  16. EP260227a: COLIBRÍ optical observations
  17. EP260227a: NOT optical observations
  18. GRB 260225A: SVOM/VT optical continued observations and upper limit
  19. GRID detection of GRB 260223A
  20. EP260227a: Global MASTER-Net observations report
  21. EP260227a: Einstein Probe detection of an X-ray transient and refined analysis
  22. The EP-WXT trigger 01709258681 (EP260227a?): Las Cumbres follow-up observation of the optical counterpart
  23. EP/WXT trigger 01709258681 (EP260227a?): LCO candidate afterglow
  24. IceCube cascade alert 142200_1517143 retraction
  25. GRB 260226A: Insight-HXMT/HE detection of the very bright burst
  26. Konus-Wind detection of GRB 260226A
  27. GRB 260223A: 7DT detection and Medium-band SED of Afterglow
  28. EP260214a: VLT/FORS2 optical observations
  29. GRB 260225A: WINTER J-band upper limit
  30. GRB 260226A: CALET Gamma-Ray Burst Monitor detection
  31. GRB 260226A: COLIBRÍ optical upper limits
  32. GRB 260226A: LCOGT Optical Upper Limit
  33. EP-WXT trigger 01709258652: SVOM/C-GFT confirmation of a stellar flare
  34. GRB 260225D: Glowbug gamma-ray detection of a likely short burst
  35. GRB 260226A: Glowbug gamma-ray detection
  36. GRB 260226A: NuSTAR detection of bright prompt emission
  37. GRB 260226A : GROWTH-India Telescope optical observations
  38. GRB 260226A: LAST optical upper limit
  39. GRB 260226A: Fermi GBM observation
  40. GRB 260226A: Fermi-LAT refined analysis
  41. The EP-WXT trigger 01709258652 is likely a flaring star
  42. LAT GRB260226.44: Global MASTER-Net observations report
  43. Fermi GRB 260226A: Global MASTER-Net observations report
  44. GRB 260226A: AstroSat CZTI detection of bright long burst
  45. EP260214a: VLA 6 GHz detection
  46. GRB 260226A: Fermi-LAT detection of a bright burst
  47. GRB 260226A???: BALROG localization (Fermi Trigger 793795080 / GRB 260226443)
  48. EP260224a: LCO optical upper limits
  49. GRB260225A: SVOM/ECLAIRs refined position
  50. GRB 260226A: Fermi GBM Final Real-time Localization
  51. GRB 260225A: EP-FXT follow-up observation
  52. GRB 260225A: SVOM/VT optical observation
  53. GRB 260225A: SVOM/COLIBRÍ (FM-GFT) Detection of an Optical Counterpart Candidate
  54. GRB 260225C: Fermi GBM Final Real-time Localization
  55. GRB 260223A: Fermi GBM Observation
  56. GRB 260225A: SVOM/VT optical upper limits
  57. GRB 260225B: Fermi GBM Final Real-time Localization
  58. EP260126a: VLA 6 GHz detection
  59. EP260223a: Liverpool Telescope upper limits
  60. GRB 260225A: SVOM/COLIBRÍ (FM-GFT) optical upper limits
  61. GRB 260225A: SVOM detection of a burst
  62. EP260224a: Einstein Probe detection of an X-ray transient
  63. EP 260225.148: COLIBRÍ Confirmation of flaring star
  64. EP260223a: Xinglong optical upper limit
  65. The EP-WXT trigger 01709258631 is likely a flaring star
  66. GRB 260223A: Glowbug gamma-ray detection
  67. EP260213a: Mephisto optical upper limits
  68. EP260223a: EP-FXT follow-up observation
  69. sb26021801: SVOM/VT optical upper limits
  70. GRB 260223A: COLIBRÍ optical afterglow decay confirmation
  71. sb26021801: SVOM/C-GFT upper limit
  72. EP260223a: COLIBRÍ optical upper limits
  73. EP260223a: Einstein Probe detection of an X-ray transient
  74. GRB 260223A: SVOM/VT optical observation
  75. GRB 260223A: SVOM/GRM observation
  76. GRB 260223A: COLIBRÍ further optical observations and a brightening
  77. EP260221a: Optical upper limit with Kinder observations
  78. GRB 260223A: COLIBRÍ optical observations
  79. GRB 260223A: DDOTI Optical Candidate
  80. GRB 260223A: BALROG localization (Fermi Trigger 793512674 / GRB 260223174)
  81. Fermi GRB 260223A: Global MASTER-Net observations report
  82. GRB 260223A: Fermi GBM Final Real-time Localization
  83. EP260221a: Liverpool Telescope detection of COLIBRÍ counterpart candidate
  84. EP260221a: COLIBRÍ optical counterpart candidate
  85. EP260221a: Gemini South z-band upper limit
  86. GRB 260222A: Fermi GBM Final Real-time Localization
  87. EP260221a: Global MASTER-Net observations report
  88. EP260221a: EP-FXT follow-up observation
  89. Fermi GRB 260221B: Global MASTER-Net observations report
  90. GRB 260221B: Fermi GBM Final Real-time Localization
  91. EP-WXT01709258519: Xinglong optical upper limit
  92. EP260221a: Xinglong optical upper limit
  93. Fermi GRB 260221A: Global MASTER-Net observations report
  94. ZTF26aaglqak/AT2026dbl: COLIBRÍ Optical Observations
  95. GRB 260221A: Fermi GBM Final Real-time Localization
  96. EP260221a: GOTO optical upper limit
  97. EP260221a: COLIBRÍ optical upper limit
  98. SVOM alert sb26021801: LCO optical upper limit
  99. EP260221a: Einstein Probe detection of an X-ray transient
  100. The EP-WXT trigger 01709258519 is likely caused by Mrk 421

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