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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. GRB 250221A: REM optical/NIR afterglow detection
  2. IceCube-250207A: MASTER flaring blazar QSOJ0854+2006 with Zhirkov effect
  3. GRB 250221A: Enhanced Swift-XRT position
  4. LIGO/Virgo/KAGRA S250221eb: Retraction of GW compact binary merger candidate
  5. EP250220a: 1.6m Mephisto observations
  6. EP250220a: Liverpool Telescope optical upper limits
  7. EP250220a: Optical upper limit with Kinder observations
  8. SVOM trigger sb25022102 is not an astrophysical event
  9. SVOM/sb25022102: SVOM detection of an X-ray transient
  10. GRB 250221A: COLIBRÍ/DDRAGO Confirmation of a Bright Optical Counterpart
  11. GRB 250221A: Swift detection of a burst with an optical counterpart
  12. Swift GRB250221.15: Global MASTER-Net OT detection
  13. Swift GRB250221.15: Global MASTER-Net observations report
  14. EP250220a: Xinglong optical upper limit
  15. Fermi Gamma-ray Burst Monitor trigger 761788229/250220993 is not a GRB
  16. GRB 250220B: Fermi GBM Final Real-time Localization
  17. Fermi Gamma-ray Burst Monitor trigger 761782146/250220923 is not a GRB
  18. GRB 250220A: Fermi GBM Final Real-time Localization
  19. EP250220a: Global MASTER-Net observations report
  20. EP250220a: EP-WXT detection of a fast X-ray transient
  21. Konus-Wind detection of GRB 250217C (short)
  22. GRB 250219A: Swift/UVOT Upper Limits
  23. GRB 250219A: OHP/T193 optical upper limit
  24. GRB 250219A: NOT optical observations
  25. GRB 250219A: COLIBRÍ/DDRAGO Detection of the Optical Counterpart
  26. GRB 250219A: 1.6m Mephisto optical upper limits
  27. GRB 250219A: SVOM/VT optical counterpart
  28. GRB 250219A: Swift-XRT observations
  29. LIGO/Virgo/KAGRA S250206dm: Upper limits from MSU cubesats observations
  30. GRB 250219A: Swift ToO observations
  31. GRB 250219A: SVOM detection of a burst
  32. Konus-Wind detection of GRB 250215A / EP250215a
  33. SVOM/sb25021804: COLIBRÍ/DDRAGO Confirmation of Variability
  34. GRB 250217C: Swift-XRT observations
  35. SVOM/sb25021804: QSO variability in Liverpool Telescope observations
  36. GRB 250217C: COLIBRÍ/DDRAGO Upper Limits on the Optical Counterpart
  37. GRB 250217C: DDOTI Upper Limits on the Optical Afterglow
  38. GRB 250217C: SVOM/GRM observation
  39. GRB 250217C: Tiled Swift observations
  40. GRB 250217C: Fermi GBM Observation
  41. GRB 250215A / EP250215A: Encouraging Follow-up Observations of a BdHN I with a Rest-Frame Duration 2.3 s at z=4.61
  42. IPN triangulation of GRB 250217C (short)
  43. Transient SVOM/sb25021804: COLIBRÍ/DDRAGO Optical Upper Limits on the Optical Counterpart
  44. SVOM/sb25021804: SVOM detection of a long X-ray transient
  45. GRB 250213A: Swift-XRT observations
  46. LIGO/Virgo/KAGRA S250206dm: AZT-33IK Target Optical Observations
  47. GRB 250216A: AstroSat CZTI detection
  48. GRB 250217C: AstroSat CZTI detection of a short burst
  49. Fermi GRB 250217C: Global MASTER-Net observations report
  50. GRB 250217C: Fermi GBM Final Real-time Localization
  51. IceCube-Cascade 250215A: Upper limits from a search for additional neutrino events in IceCube
  52. LIGO/Virgo/KAGRA S250206dm: observation in AbAO, optical transient near NED/GLADE+ galaxy WISEA J021210.14+514821.7
  53. Fermi GRB 250217A: Global MASTER-Net observations report
  54. GRANDMA/OPD observations of GRB250215A
  55. GRB 250217B: Fermi GBM Final Real-time Localization
  56. The EP-WXT trigger 01709131775 is likely a flaring star
  57. GRB 250217A: Fermi GBM Final Real-time Localization
  58. Fermi GRB 250216A: Global MASTER-Net observations report
  59. GRB 250215A / EP250215a: LCO detection of the afterglow
  60. GRB 250216A: Fermi GBM Final Real-time Localization
  61. EP250212a: FTW optical and NIR upper limits
  62. GRB 250215A: Swift/UVOT Upper Limits
  63. GRB 250215A: COLIBRÍ/DDRAGO Optical Upper Limits on the Afterglow
  64. EP250215a / GRB 250215A : GTC redshift z = 4.61
  65. GRB 250215A: Fermi GBM Observation
  66. EP250215a / GRB 250215A : NOT optical observations
  67. GRB 250215A/EP250215a: 1.6m Mephisto optical observation report
  68. GRB 250215A / EP250215a: Gemini-South optical observation of a likely rebrightening
  69. LIGO/Virgo/KAGRA S250206dm: MASTER LC AT2025bbo
  70. GRB 250213A: COLIBRÍ/DDRAGO Optical Upper Limits on the Afterglow
  71. GRB 250215A: Swift-XRT refined Analysis
  72. GRB 250215A: SVOM/GRM observation
  73. EP250215a / GRB 250215A: AstroSat CZTI detection
  74. GRB 250215A / EP250215a: SVOM/VT optical candidate comfirmation
  75. EP250215a: Global MASTER-Net observations report
  76. EP250215A/GRB 250215A: INTEGRAL SPI-ACS detection
  77. EP250215a / GRB 250215A (potentially): NOT likely optical counterpart
  78. EP250215a: EP-WXT detection and FXT follow-up observation of an X-ray transient
  79. Fermi GRB 250215A: Global MASTER-Net observations report
  80. GRB 250215A: Fermi GBM Final Real-time Localization
  81. Fermi trigger No 761206993: Global MASTER-Net observations report
  82. GRB 250213A：SVOM/VT optical candidate
  83. Fermi Gamma-ray Burst Monitor trigger 761206993/250214266 is not a GRB
  84. EP250207b: Xinglong optical upper limit
  85. Fermi GRB 250214A: Global MASTER-Net observations report
  86. GRB 250213A: Swift ToO observations
  87. GRB 250214A: Fermi GBM Final Real-time Localization
  88. EP250212a: Xinglong optical upper limit
  89. LIGO/Virgo/KAGRA S250206dm: DECam GW-MMADS candidates
  90. GRB 250213A: SVOM detection of a burst
  91. EP250212a: Global MASTER-Net observations report
  92. GRB 250205A: VIRT Optical Upper Limit
  93. GRB 250205A: Leavitt Observatory optical upper limit
  94. GRB 250210A: GRBAlpha detection
  95. EP250207B: Chandra localization of the X-ray counterpart
  96. LIGO/Virgo/KAGRA S250206dm: FTW observations of counterpart candidates AT2025bbo and AT2025bcx, and of NED galaxies
  97. EP250207b: VLA radio upper limits
  98. EP250212a: Liverpool Telescope optical upper limits
  99. EP250212a: EP-WXT detection and FXT follow-up observation of a fast X-ray transient
  100. GRB250101A: Radio upper limits from GMRT observations

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