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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"

28100 results found.

  1. GRB 250210A: VZLUSAT-2 detection
  2. GRB 250206A: VZLUSAT-2 detection
  3. EP250223a: REM NIR upper limit
  4. EP250223a: TRT optical afterglow observation
  5. EP250223a: refined analysis of the EP-WXT and FXT observations
  6. EP250223a: 1.6m Mephisto and 50cm array observations
  7. GRB 250221A: TNOT detection of the optical counterpart
  8. EP250223a: SVOM/VT optical observation
  9. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO trigger with ID 762004910: Identification of a GW compact binary merger candidate possibly associated with a sub-threshold Swift/BAT-GUANO trigger
  10. EP250223a: OASDG optical observations
  11. EP250223a: LCO detection of the afterglow
  12. EP250223a: early optical detection by BOOTES-4
  13. EP250223a: NOT redshift z = 2.756
  14. EP250223a: Swift/XRT localization
  15. EP250223a: NOT optical afterglow candidate
  16. GRB 250223B: Fermi GBM Final Localization
  17. GRB 250221A: VLA radio detection
  18. GRB 250223A: Fermi GBM Final Real-time Localization
  19. EP250223a: Einstein Probe detection of an X-ray transient
  20. GRB 250221A: continued Assy optical observations, brightening afterglow confirmation
  21. GRB 250221A: continued Mondy optical observations, brightening afterglow
  22. GRB 250221A: Optical counterpart detection by LCO.
  23. GRB 250221A: Mondy optical observations
  24. Konus-Wind detection of GRB 250221A
  25. GRB 250221A: Assy optical observations
  26. EP250220a: EP-FXT follow-up observations
  27. GRB 250219A: NUTTelA-TAO / BSTI Optical Limits
  28. GRB 250221A: VLT/X-shooter redshift z = 0.768
  29. GRB 250221A: GRANDMA/TAROT Detection
  30. GRB 250221A: Swift-XRT refined Analysis
  31. GRB 250221A: NOT optical observations
  32. GRB 250221A: 1.6m Mephisto optical detection
  33. GRB 250221A: AKO Optical Upper Limit
  34. GRB 250221A: Swift/UVOT Detection
  35. GRB 250219A: GRANDMA/Kilonova-Catcher upper limits
  36. GRB 250221A: REM optical/NIR afterglow detection
  37. GRB 250221A: Enhanced Swift-XRT position
  38. EP250220a: Liverpool Telescope optical upper limits
  39. EP250220a: Optical upper limit with Kinder observations
  40. SVOM trigger sb25022102 is not an astrophysical event
  41. SVOM/sb25022102: SVOM detection of an X-ray transient
  42. GRB 250221A: Swift detection of a burst with an optical counterpart
  43. Swift GRB250221.15: Global MASTER-Net OT detection
  44. EP250220a: Xinglong optical upper limit
  45. GRB 250220B: Fermi GBM Final Real-time Localization
  46. GRB 250220A: Fermi GBM Final Real-time Localization
  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. GRB 250219A: Swift ToO observations
  57. GRB 250219A: SVOM detection of a burst
  58. Konus-Wind detection of GRB 250215A / EP250215a
  59. GRB 250217C: Swift-XRT observations
  60. SVOM/sb25021804: QSO variability in Liverpool Telescope observations
  61. GRB 250217C: COLIBRÍ/DDRAGO Upper Limits on the Optical Counterpart
  62. GRB 250217C: DDOTI Upper Limits on the Optical Afterglow
  63. GRB 250217C: Tiled Swift observations
  64. GRB 250215A / EP250215A: Encouraging Follow-up Observations of a BdHN I with a Rest-Frame Duration 2.3 s at z=4.61
  65. IPN triangulation of GRB 250217C (short)
  66. Transient SVOM/sb25021804: COLIBRÍ/DDRAGO Optical Upper Limits on the Optical Counterpart
  67. SVOM/sb25021804: SVOM detection of a long X-ray transient
  68. GRB 250213A: Swift-XRT observations
  69. GRB 250216A: AstroSat CZTI detection
  70. GRB 250217C: AstroSat CZTI detection of a short burst
  71. GRB 250217C: Fermi GBM Final Real-time Localization
  72. GRANDMA/OPD observations of GRB250215A
  73. GRB 250217B: Fermi GBM Final Real-time Localization
  74. GRB 250217A: Fermi GBM Final Real-time Localization
  75. GRB 250215A / EP250215a: LCO detection of the afterglow
  76. GRB 250216A: Fermi GBM Final Real-time Localization
  77. GRB 250215A: Swift/UVOT Upper Limits
  78. GRB 250215A: COLIBRÍ/DDRAGO Optical Upper Limits on the Afterglow
  79. EP250215a / GRB 250215A : GTC redshift z = 4.61
  80. GRB 250215A: Fermi GBM Observation
  81. EP250215a / GRB 250215A : NOT optical observations
  82. GRB 250215A/EP250215a: 1.6m Mephisto optical observation report
  83. GRB 250215A / EP250215a: Gemini-South optical observation of a likely rebrightening
  84. GRB 250213A: COLIBRÍ/DDRAGO Optical Upper Limits on the Afterglow
  85. GRB 250215A: Swift-XRT refined Analysis
  86. EP250215a / GRB 250215A: AstroSat CZTI detection
  87. EP250215A/GRB 250215A: INTEGRAL SPI-ACS detection
  88. EP250215a: EP-WXT detection and FXT follow-up observation of an X-ray transient
  89. GRB 250215A: Fermi GBM Final Real-time Localization
  90. EP250207b: Xinglong optical upper limit
  91. GRB 250213A: Swift ToO observations
  92. GRB 250214A: Fermi GBM Final Real-time Localization
  93. EP250212a: Xinglong optical upper limit
  94. GRB 250213A: SVOM detection of a burst
  95. GRB 250205A: VIRT Optical Upper Limit
  96. GRB 250205A: Leavitt Observatory optical upper limit
  97. GRB 250210A: GRBAlpha detection
  98. EP250207B: Chandra localization of the X-ray counterpart
  99. LIGO/Virgo/KAGRA S250206dm: FTW observations of counterpart candidates AT2025bbo and AT2025bcx, and of NED galaxies
  100. EP250212a: Liverpool Telescope optical upper limits

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