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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. LAT GRB260226.44: Global MASTER-Net observations report
  2. Fermi GRB 260226A: Global MASTER-Net observations report
  3. GRB 260226A: AstroSat CZTI detection of bright long burst
  4. EP260214a: VLA 6 GHz detection
  5. GRB 260226A: Fermi-LAT detection of a bright burst
  6. GRB 260226A???: BALROG localization (Fermi Trigger 793795080 / GRB 260226443)
  7. EP260224a: LCO optical upper limits
  8. GRB260225A: SVOM/ECLAIRs refined position
  9. GRB 260226A: Fermi GBM Final Real-time Localization
  10. GRB 260225A: EP-FXT follow-up observation
  11. GRB 260225A: SVOM/VT optical observation
  12. GRB 260225A: SVOM/COLIBRÍ (FM-GFT) Detection of an Optical Counterpart Candidate
  13. GRB 260225C: Fermi GBM Final Real-time Localization
  14. GRB 260223A: Fermi GBM Observation
  15. GRB 260225A: SVOM/VT optical upper limits
  16. GRB 260225B: Fermi GBM Final Real-time Localization
  17. EP260126a: VLA 6 GHz detection
  18. EP260223a: Liverpool Telescope upper limits
  19. GRB 260225A: SVOM/COLIBRÍ (FM-GFT) optical upper limits
  20. GRB 260225A: SVOM detection of a burst
  21. EP260224a: Einstein Probe detection of an X-ray transient
  22. EP 260225.148: COLIBRÍ Confirmation of flaring star
  23. EP260223a: Xinglong optical upper limit
  24. The EP-WXT trigger 01709258631 is likely a flaring star
  25. GRB 260223A: Glowbug gamma-ray detection
  26. EP260213a: Mephisto optical upper limits
  27. EP260223a: EP-FXT follow-up observation
  28. sb26021801: SVOM/VT optical upper limits
  29. GRB 260223A: COLIBRÍ optical afterglow decay confirmation
  30. sb26021801: SVOM/C-GFT upper limit
  31. EP260223a: COLIBRÍ optical upper limits
  32. EP260223a: Einstein Probe detection of an X-ray transient
  33. GRB 260223A: SVOM/VT optical observation
  34. GRB 260223A: SVOM/GRM observation
  35. GRB 260223A: COLIBRÍ further optical observations and a brightening
  36. EP260221a: Optical upper limit with Kinder observations
  37. GRB 260223A: COLIBRÍ optical observations
  38. GRB 260223A: DDOTI Optical Candidate
  39. GRB 260223A: BALROG localization (Fermi Trigger 793512674 / GRB 260223174)
  40. Fermi GRB 260223A: Global MASTER-Net observations report
  41. GRB 260223A: Fermi GBM Final Real-time Localization
  42. EP260221a: Liverpool Telescope detection of COLIBRÍ counterpart candidate
  43. EP260221a: COLIBRÍ optical counterpart candidate
  44. EP260221a: Gemini South z-band upper limit
  45. GRB 260222A: Fermi GBM Final Real-time Localization
  46. EP260221a: Global MASTER-Net observations report
  47. EP260221a: EP-FXT follow-up observation
  48. Fermi GRB 260221B: Global MASTER-Net observations report
  49. GRB 260221B: Fermi GBM Final Real-time Localization
  50. EP-WXT01709258519: Xinglong optical upper limit
  51. EP260221a: Xinglong optical upper limit
  52. Fermi GRB 260221A: Global MASTER-Net observations report
  53. ZTF26aaglqak/AT2026dbl: COLIBRÍ Optical Observations
  54. GRB 260221A: Fermi GBM Final Real-time Localization
  55. EP260221a: GOTO optical upper limit
  56. EP260221a: COLIBRÍ optical upper limit
  57. SVOM alert sb26021801: LCO optical upper limit
  58. EP260221a: Einstein Probe detection of an X-ray transient
  59. The EP-WXT trigger 01709258519 is likely caused by Mrk 421
  60. GRB 260219A: AstroSat CZTI detection
  61. IceCube-260217A: Upper limits from a search for additional neutrino events in IceCube
  62. GRB 260219A: GECAM-B observation of a long burst
  63. Fermi GRB 260219A: Global MASTER-Net observations report
  64. GRB 260219A: Fermi GBM Final Real-time Localization
  65. SVOM alert sb26021801: LAST optical upper limit
  66. sb26021801: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  67. IceCube Alert 260217A: Global MASTER-Net observations report
  68. Fermi-LAT Gamma-ray Observations of IceCube-260217A
  69. GRB 260217A: Fermi GBM Final Localization
  70. GRB 260214B/EP260214b: SVOM/ECLAIRs detection through targeted search
  71. sb26021801: SVOM detection of a long faint X-ray transient
  72. The EP-WXT trigger 01709258455 is likely a flaring star
  73. EP-WXT 01709258455: NOT optical upper limits
  74. EP260214b: Mondy optical observations
  75. EP260214b: 1.3m DFOT optical upper limit
  76. EP260210a: Mondy optical upper limits
  77. Konus-Wind detection of GRB 260212A
  78. GRB 260208A: AbAO and Terskol optical upper limits
  79. GRB 260208A: continued Mondy optical observations
  80. IPN triangulation of GRB 260212A
  81. IceCube-260217A - IceCube observation of a high-energy neutrino candidate track-like event
  82. GRB 260213A: GECAM-B observation of a short burst
  83. GRB 260216A: Fermi Gamma-ray Burst Monitor trigger 792969362/260216886 is not a GRB
  84. GRB 260216A: Fermi GBM Final Real-time Localization
  85. EP260214b: Liverpool Telescope optical observations
  86. GRB 260206A: probable hard X-ray burst from 4U 0513-40
  87. EP260214b: Optical upper limit with Kinder observations
  88. EP260214a: Optical upper limits with Kinder observations
  89. EP260214b: EP-FXT follow-up observation
  90. EP260214a / GRB 260214A: Fermi-GBM Sub-Threshold Detection
  91. EP260214b: DDOTI Optical Detection
  92. EP260214b: GROWTH-India Telescope optical upper limit
  93. EP260214a: VLT near-infrared observation
  94. EP260214b: SVOM/VT optical observation
  95. EP260214a: NOT optical upper limits
  96. EP260214a: COLIBRÍ optical upper limits
  97. EP260214b: OHP/T120 optical observations
  98. EP260214a: refined analysis of the EP-FXT observation
  99. EP260214b: LCO optical counterpart detection
  100. EP260214b: VLT/X-shooter spectroscopic redshift z = 1.208

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