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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: Mondy optical observations
  2. Konus-Wind detection of GRB 250221A
  3. GRB 250221A: Assy optical observations
  4. EP250220a: FTW optical and NIR observations and upper limits
  5. EP250220a: EP-FXT follow-up observations
  6. GRB 250219A: NUTTelA-TAO / BSTI Optical Limits
  7. GRB 250221A: VLT/X-shooter redshift z = 0.768
  8. GRB 250221A: GRANDMA/TAROT Detection
  9. Fermi trigger No 761805304: Global MASTER-Net observations report
  10. Fermi Gamma-ray Burst Monitor trigger 761867337/250221909 is not a GRB
  11. GRB 250221A: Swift-XRT refined Analysis
  12. GRB 250221A: NOT optical observations
  13. GRB 250221A: 1.6m Mephisto optical detection
  14. LIGO/Virgo/KAGRA S250221gb: Retraction of GW compact binary merger candidate
  15. GRB 250221A: AKO Optical Upper Limit
  16. GRB 250221A: Swift/UVOT Detection
  17. EP250220a: Liverpool Telescope upper limits
  18. GRB 250219A: GRANDMA/Kilonova-Catcher upper limits
  19. GRB 250221A: REM optical/NIR afterglow detection
  20. IceCube-250207A: MASTER flaring blazar QSOJ0854+2006 with Zhirkov effect
  21. GRB 250221A: Enhanced Swift-XRT position
  22. LIGO/Virgo/KAGRA S250221eb: Retraction of GW compact binary merger candidate
  23. EP250220a: 1.6m Mephisto observations
  24. EP250220a: Liverpool Telescope optical upper limits
  25. EP250220a: Optical upper limit with Kinder observations
  26. SVOM trigger sb25022102 is not an astrophysical event
  27. SVOM/sb25022102: SVOM detection of an X-ray transient
  28. GRB 250221A: COLIBRÍ/DDRAGO Confirmation of a Bright Optical Counterpart
  29. GRB 250221A: Swift detection of a burst with an optical counterpart
  30. Swift GRB250221.15: Global MASTER-Net OT detection
  31. Swift GRB250221.15: Global MASTER-Net observations report
  32. EP250220a: Xinglong optical upper limit
  33. Fermi Gamma-ray Burst Monitor trigger 761788229/250220993 is not a GRB
  34. GRB 250220B: Fermi GBM Final Real-time Localization
  35. Fermi Gamma-ray Burst Monitor trigger 761782146/250220923 is not a GRB
  36. GRB 250220A: Fermi GBM Final Real-time Localization
  37. EP250220a: Global MASTER-Net observations report
  38. EP250220a: EP-WXT detection of a fast X-ray transient
  39. Konus-Wind detection of GRB 250217C (short)
  40. GRB 250219A: Swift/UVOT Upper Limits
  41. GRB 250219A: OHP/T193 optical upper limit
  42. GRB 250219A: NOT optical observations
  43. GRB 250219A: COLIBRÍ/DDRAGO Detection of the Optical Counterpart
  44. GRB 250219A: 1.6m Mephisto optical upper limits
  45. GRB 250219A: SVOM/VT optical counterpart
  46. GRB 250219A: Swift-XRT observations
  47. LIGO/Virgo/KAGRA S250206dm: Upper limits from MSU cubesats observations
  48. GRB 250219A: Swift ToO observations
  49. GRB 250219A: SVOM detection of a burst
  50. Konus-Wind detection of GRB 250215A / EP250215a
  51. SVOM/sb25021804: COLIBRÍ/DDRAGO Confirmation of Variability
  52. GRB 250217C: Swift-XRT observations
  53. SVOM/sb25021804: QSO variability in Liverpool Telescope observations
  54. GRB 250217C: COLIBRÍ/DDRAGO Upper Limits on the Optical Counterpart
  55. GRB 250217C: DDOTI Upper Limits on the Optical Afterglow
  56. GRB 250217C: SVOM/GRM observation
  57. GRB 250217C: Tiled Swift observations
  58. GRB 250217C: Fermi GBM Observation
  59. GRB 250215A / EP250215A: Encouraging Follow-up Observations of a BdHN I with a Rest-Frame Duration 2.3 s at z=4.61
  60. IPN triangulation of GRB 250217C (short)
  61. Transient SVOM/sb25021804: COLIBRÍ/DDRAGO Optical Upper Limits on the Optical Counterpart
  62. SVOM/sb25021804: SVOM detection of a long X-ray transient
  63. GRB 250213A: Swift-XRT observations
  64. LIGO/Virgo/KAGRA S250206dm: AZT-33IK Target Optical Observations
  65. GRB 250216A: AstroSat CZTI detection
  66. GRB 250217C: AstroSat CZTI detection of a short burst
  67. Fermi GRB 250217C: Global MASTER-Net observations report
  68. GRB 250217C: Fermi GBM Final Real-time Localization
  69. IceCube-Cascade 250215A: Upper limits from a search for additional neutrino events in IceCube
  70. LIGO/Virgo/KAGRA S250206dm: observation in AbAO, optical transient near NED/GLADE+ galaxy WISEA J021210.14+514821.7
  71. Fermi GRB 250217A: Global MASTER-Net observations report
  72. GRANDMA/OPD observations of GRB250215A
  73. GRB 250217B: Fermi GBM Final Real-time Localization
  74. The EP-WXT trigger 01709131775 is likely a flaring star
  75. GRB 250217A: Fermi GBM Final Real-time Localization
  76. Fermi GRB 250216A: Global MASTER-Net observations report
  77. GRB 250215A / EP250215a: LCO detection of the afterglow
  78. GRB 250216A: Fermi GBM Final Real-time Localization
  79. EP250212a: FTW optical and NIR upper limits
  80. GRB 250215A: Swift/UVOT Upper Limits
  81. GRB 250215A: COLIBRÍ/DDRAGO Optical Upper Limits on the Afterglow
  82. EP250215a / GRB 250215A : GTC redshift z = 4.61
  83. GRB 250215A: Fermi GBM Observation
  84. EP250215a / GRB 250215A : NOT optical observations
  85. GRB 250215A/EP250215a: 1.6m Mephisto optical observation report
  86. GRB 250215A / EP250215a: Gemini-South optical observation of a likely rebrightening
  87. LIGO/Virgo/KAGRA S250206dm: MASTER LC AT2025bbo
  88. GRB 250213A: COLIBRÍ/DDRAGO Optical Upper Limits on the Afterglow
  89. GRB 250215A: Swift-XRT refined Analysis
  90. GRB 250215A: SVOM/GRM observation
  91. EP250215a / GRB 250215A: AstroSat CZTI detection
  92. GRB 250215A / EP250215a: SVOM/VT optical candidate comfirmation
  93. EP250215a: Global MASTER-Net observations report
  94. EP250215A/GRB 250215A: INTEGRAL SPI-ACS detection
  95. EP250215a / GRB 250215A (potentially): NOT likely optical counterpart
  96. EP250215a: EP-WXT detection and FXT follow-up observation of an X-ray transient
  97. Fermi GRB 250215A: Global MASTER-Net observations report
  98. GRB 250215A: Fermi GBM Final Real-time Localization
  99. Fermi trigger No 761206993: Global MASTER-Net observations report
  100. GRB 250213A：SVOM/VT optical candidate

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