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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').
  1. GRB 250221A: VLA radio detection
  2. Fermi GRB 250223A: Global MASTER-Net observations report
  3. Fermi trigger No 762020305: Global MASTER-Net observations report
  4. GRB 250223A: Fermi GBM Final Real-time Localization
  5. EP250223a: Einstein Probe detection of an X-ray transient
  6. LIGO/Virgo/KAGRA S250206dm: Upper limits from IceCube neutrino searches
  7. GRB 250221A: continued Assy optical observations, brightening afterglow confirmation
  8. GRB 250221A: continued Mondy optical observations, brightening afterglow
  9. GRB 250221A: Optical counterpart detection by LCO.
  10. GRB 250221A: Mondy optical observations
  11. Konus-Wind detection of GRB 250221A
  12. GRB 250221A: Assy optical observations
  13. EP250220a: FTW optical and NIR observations and upper limits
  14. EP250220a: EP-FXT follow-up observations
  15. GRB 250219A: NUTTelA-TAO / BSTI Optical Limits
  16. GRB 250221A: VLT/X-shooter redshift z = 0.768
  17. GRB 250221A: GRANDMA/TAROT Detection
  18. Fermi trigger No 761805304: Global MASTER-Net observations report
  19. Fermi Gamma-ray Burst Monitor trigger 761867337/250221909 is not a GRB
  20. GRB 250221A: Swift-XRT refined Analysis
  21. GRB 250221A: NOT optical observations
  22. GRB 250221A: 1.6m Mephisto optical detection
  23. LIGO/Virgo/KAGRA S250221gb: Retraction of GW compact binary merger candidate
  24. GRB 250221A: AKO Optical Upper Limit
  25. GRB 250221A: Swift/UVOT Detection
  26. EP250220a: Liverpool Telescope upper limits
  27. GRB 250219A: GRANDMA/Kilonova-Catcher upper limits
  28. GRB 250221A: REM optical/NIR afterglow detection
  29. IceCube-250207A: MASTER flaring blazar QSOJ0854+2006 with Zhirkov effect
  30. GRB 250221A: Enhanced Swift-XRT position
  31. LIGO/Virgo/KAGRA S250221eb: Retraction of GW compact binary merger candidate
  32. EP250220a: 1.6m Mephisto observations
  33. EP250220a: Liverpool Telescope optical upper limits
  34. EP250220a: Optical upper limit with Kinder observations
  35. SVOM trigger sb25022102 is not an astrophysical event
  36. SVOM/sb25022102: SVOM detection of an X-ray transient
  37. GRB 250221A: COLIBRÍ/DDRAGO Confirmation of a Bright Optical Counterpart
  38. GRB 250221A: Swift detection of a burst with an optical counterpart
  39. Swift GRB250221.15: Global MASTER-Net OT detection
  40. Swift GRB250221.15: Global MASTER-Net observations report
  41. EP250220a: Xinglong optical upper limit
  42. Fermi Gamma-ray Burst Monitor trigger 761788229/250220993 is not a GRB
  43. GRB 250220B: Fermi GBM Final Real-time Localization
  44. Fermi Gamma-ray Burst Monitor trigger 761782146/250220923 is not a GRB
  45. GRB 250220A: Fermi GBM Final Real-time Localization
  46. EP250220a: Global MASTER-Net observations report
  47. EP250220a: EP-WXT detection of a fast X-ray transient
  48. Konus-Wind detection of GRB 250217C (short)
  49. GRB 250219A: Swift/UVOT Upper Limits
  50. GRB 250219A: OHP/T193 optical upper limit
  51. GRB 250219A: NOT optical observations
  52. GRB 250219A: COLIBRÍ/DDRAGO Detection of the Optical Counterpart
  53. GRB 250219A: 1.6m Mephisto optical upper limits
  54. GRB 250219A: SVOM/VT optical counterpart
  55. GRB 250219A: Swift-XRT observations
  56. LIGO/Virgo/KAGRA S250206dm: Upper limits from MSU cubesats observations
  57. GRB 250219A: Swift ToO observations
  58. GRB 250219A: SVOM detection of a burst
  59. Konus-Wind detection of GRB 250215A / EP250215a
  60. SVOM/sb25021804: COLIBRÍ/DDRAGO Confirmation of Variability
  61. GRB 250217C: Swift-XRT observations
  62. SVOM/sb25021804: QSO variability in Liverpool Telescope observations
  63. GRB 250217C: COLIBRÍ/DDRAGO Upper Limits on the Optical Counterpart
  64. GRB 250217C: DDOTI Upper Limits on the Optical Afterglow
  65. GRB 250217C: SVOM/GRM observation
  66. GRB 250217C: Tiled Swift observations
  67. GRB 250217C: Fermi GBM Observation
  68. GRB 250215A / EP250215A: Encouraging Follow-up Observations of a BdHN I with a Rest-Frame Duration 2.3 s at z=4.61
  69. IPN triangulation of GRB 250217C (short)
  70. Transient SVOM/sb25021804: COLIBRÍ/DDRAGO Optical Upper Limits on the Optical Counterpart
  71. SVOM/sb25021804: SVOM detection of a long X-ray transient
  72. GRB 250213A: Swift-XRT observations
  73. LIGO/Virgo/KAGRA S250206dm: AZT-33IK Target Optical Observations
  74. GRB 250216A: AstroSat CZTI detection
  75. GRB 250217C: AstroSat CZTI detection of a short burst
  76. Fermi GRB 250217C: Global MASTER-Net observations report
  77. GRB 250217C: Fermi GBM Final Real-time Localization
  78. IceCube-Cascade 250215A: Upper limits from a search for additional neutrino events in IceCube
  79. LIGO/Virgo/KAGRA S250206dm: observation in AbAO, optical transient near NED/GLADE+ galaxy WISEA J021210.14+514821.7
  80. Fermi GRB 250217A: Global MASTER-Net observations report
  81. GRANDMA/OPD observations of GRB250215A
  82. GRB 250217B: Fermi GBM Final Real-time Localization
  83. The EP-WXT trigger 01709131775 is likely a flaring star
  84. GRB 250217A: Fermi GBM Final Real-time Localization
  85. Fermi GRB 250216A: Global MASTER-Net observations report
  86. GRB 250215A / EP250215a: LCO detection of the afterglow
  87. GRB 250216A: Fermi GBM Final Real-time Localization
  88. EP250212a: FTW optical and NIR upper limits
  89. GRB 250215A: Swift/UVOT Upper Limits
  90. GRB 250215A: COLIBRÍ/DDRAGO Optical Upper Limits on the Afterglow
  91. EP250215a / GRB 250215A : GTC redshift z = 4.61
  92. GRB 250215A: Fermi GBM Observation
  93. EP250215a / GRB 250215A : NOT optical observations
  94. GRB 250215A/EP250215a: 1.6m Mephisto optical observation report
  95. GRB 250215A / EP250215a: Gemini-South optical observation of a likely rebrightening
  96. LIGO/Virgo/KAGRA S250206dm: MASTER LC AT2025bbo
  97. GRB 250213A: COLIBRÍ/DDRAGO Optical Upper Limits on the Afterglow
  98. GRB 250215A: Swift-XRT refined Analysis
  99. GRB 250215A: SVOM/GRM observation
  100. EP250215a / GRB 250215A: AstroSat CZTI detection

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