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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: Swift-XRT refined Analysis
  2. GRB 250221A: NOT optical observations
  3. GRB 250221A: 1.6m Mephisto optical detection
  4. LIGO/Virgo/KAGRA S250221gb: Retraction of GW compact binary merger candidate
  5. GRB 250221A: AKO Optical Upper Limit
  6. GRB 250221A: Swift/UVOT Detection
  7. EP250220a: Liverpool Telescope upper limits
  8. GRB 250219A: GRANDMA/Kilonova-Catcher upper limits
  9. GRB 250221A: REM optical/NIR afterglow detection
  10. IceCube-250207A: MASTER flaring blazar QSOJ0854+2006 with Zhirkov effect
  11. GRB 250221A: Enhanced Swift-XRT position
  12. LIGO/Virgo/KAGRA S250221eb: Retraction of GW compact binary merger candidate
  13. EP250220a: 1.6m Mephisto observations
  14. EP250220a: Liverpool Telescope optical upper limits
  15. EP250220a: Optical upper limit with Kinder observations
  16. SVOM trigger sb25022102 is not an astrophysical event
  17. SVOM/sb25022102: SVOM detection of an X-ray transient
  18. GRB 250221A: COLIBRÍ/DDRAGO Confirmation of a Bright Optical Counterpart
  19. GRB 250221A: Swift detection of a burst with an optical counterpart
  20. Swift GRB250221.15: Global MASTER-Net OT detection
  21. Swift GRB250221.15: Global MASTER-Net observations report
  22. EP250220a: Xinglong optical upper limit
  23. Fermi Gamma-ray Burst Monitor trigger 761788229/250220993 is not a GRB
  24. GRB 250220B: Fermi GBM Final Real-time Localization
  25. Fermi Gamma-ray Burst Monitor trigger 761782146/250220923 is not a GRB
  26. GRB 250220A: Fermi GBM Final Real-time Localization
  27. EP250220a: Global MASTER-Net observations report
  28. EP250220a: EP-WXT detection of a fast X-ray transient
  29. Konus-Wind detection of GRB 250217C (short)
  30. GRB 250219A: Swift/UVOT Upper Limits
  31. GRB 250219A: OHP/T193 optical upper limit
  32. GRB 250219A: NOT optical observations
  33. GRB 250219A: COLIBRÍ/DDRAGO Detection of the Optical Counterpart
  34. GRB 250219A: 1.6m Mephisto optical upper limits
  35. GRB 250219A: SVOM/VT optical counterpart
  36. GRB 250219A: Swift-XRT observations
  37. LIGO/Virgo/KAGRA S250206dm: Upper limits from MSU cubesats observations
  38. GRB 250219A: Swift ToO observations
  39. GRB 250219A: SVOM detection of a burst
  40. Konus-Wind detection of GRB 250215A / EP250215a
  41. SVOM/sb25021804: COLIBRÍ/DDRAGO Confirmation of Variability
  42. GRB 250217C: Swift-XRT observations
  43. SVOM/sb25021804: QSO variability in Liverpool Telescope observations
  44. GRB 250217C: COLIBRÍ/DDRAGO Upper Limits on the Optical Counterpart
  45. GRB 250217C: DDOTI Upper Limits on the Optical Afterglow
  46. GRB 250217C: SVOM/GRM observation
  47. GRB 250217C: Tiled Swift observations
  48. GRB 250217C: Fermi GBM Observation
  49. GRB 250215A / EP250215A: Encouraging Follow-up Observations of a BdHN I with a Rest-Frame Duration 2.3 s at z=4.61
  50. IPN triangulation of GRB 250217C (short)
  51. Transient SVOM/sb25021804: COLIBRÍ/DDRAGO Optical Upper Limits on the Optical Counterpart
  52. SVOM/sb25021804: SVOM detection of a long X-ray transient
  53. GRB 250213A: Swift-XRT observations
  54. LIGO/Virgo/KAGRA S250206dm: AZT-33IK Target Optical Observations
  55. GRB 250216A: AstroSat CZTI detection
  56. GRB 250217C: AstroSat CZTI detection of a short burst
  57. Fermi GRB 250217C: Global MASTER-Net observations report
  58. GRB 250217C: Fermi GBM Final Real-time Localization
  59. IceCube-Cascade 250215A: Upper limits from a search for additional neutrino events in IceCube
  60. LIGO/Virgo/KAGRA S250206dm: observation in AbAO, optical transient near NED/GLADE+ galaxy WISEA J021210.14+514821.7
  61. Fermi GRB 250217A: Global MASTER-Net observations report
  62. GRANDMA/OPD observations of GRB250215A
  63. GRB 250217B: Fermi GBM Final Real-time Localization
  64. The EP-WXT trigger 01709131775 is likely a flaring star
  65. GRB 250217A: Fermi GBM Final Real-time Localization
  66. Fermi GRB 250216A: Global MASTER-Net observations report
  67. GRB 250215A / EP250215a: LCO detection of the afterglow
  68. GRB 250216A: Fermi GBM Final Real-time Localization
  69. EP250212a: FTW optical and NIR upper limits
  70. GRB 250215A: Swift/UVOT Upper Limits
  71. GRB 250215A: COLIBRÍ/DDRAGO Optical Upper Limits on the Afterglow
  72. EP250215a / GRB 250215A : GTC redshift z = 4.61
  73. GRB 250215A: Fermi GBM Observation
  74. EP250215a / GRB 250215A : NOT optical observations
  75. GRB 250215A/EP250215a: 1.6m Mephisto optical observation report
  76. GRB 250215A / EP250215a: Gemini-South optical observation of a likely rebrightening
  77. LIGO/Virgo/KAGRA S250206dm: MASTER LC AT2025bbo
  78. GRB 250213A: COLIBRÍ/DDRAGO Optical Upper Limits on the Afterglow
  79. GRB 250215A: Swift-XRT refined Analysis
  80. GRB 250215A: SVOM/GRM observation
  81. EP250215a / GRB 250215A: AstroSat CZTI detection
  82. GRB 250215A / EP250215a: SVOM/VT optical candidate comfirmation
  83. EP250215a: Global MASTER-Net observations report
  84. EP250215A/GRB 250215A: INTEGRAL SPI-ACS detection
  85. EP250215a / GRB 250215A (potentially): NOT likely optical counterpart
  86. EP250215a: EP-WXT detection and FXT follow-up observation of an X-ray transient
  87. Fermi GRB 250215A: Global MASTER-Net observations report
  88. GRB 250215A: Fermi GBM Final Real-time Localization
  89. Fermi trigger No 761206993: Global MASTER-Net observations report
  90. GRB 250213A：SVOM/VT optical candidate
  91. Fermi Gamma-ray Burst Monitor trigger 761206993/250214266 is not a GRB
  92. EP250207b: Xinglong optical upper limit
  93. Fermi GRB 250214A: Global MASTER-Net observations report
  94. GRB 250213A: Swift ToO observations
  95. GRB 250214A: Fermi GBM Final Real-time Localization
  96. EP250212a: Xinglong optical upper limit
  97. LIGO/Virgo/KAGRA S250206dm: DECam GW-MMADS candidates
  98. GRB 250213A: SVOM detection of a burst
  99. EP250212a: Global MASTER-Net observations report
  100. GRB 250205A: VIRT Optical Upper Limit

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