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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"

27564 results found.

  1. GRB 250221A: Enhanced Swift-XRT position
  2. EP250220a: Liverpool Telescope optical upper limits
  3. EP250220a: Optical upper limit with Kinder observations
  4. SVOM trigger sb25022102 is not an astrophysical event
  5. SVOM/sb25022102: SVOM detection of an X-ray transient
  6. GRB 250221A: Swift detection of a burst with an optical counterpart
  7. Swift GRB250221.15: Global MASTER-Net OT detection
  8. EP250220a: Xinglong optical upper limit
  9. GRB 250220B: Fermi GBM Final Real-time Localization
  10. GRB 250220A: Fermi GBM Final Real-time Localization
  11. EP250220a: EP-WXT detection of a fast X-ray transient
  12. Konus-Wind detection of GRB 250217C (short)
  13. GRB 250219A: Swift/UVOT Upper Limits
  14. GRB 250219A: OHP/T193 optical upper limit
  15. GRB 250219A: NOT optical observations
  16. GRB 250219A: COLIBRÍ/DDRAGO Detection of the Optical Counterpart
  17. GRB 250219A: 1.6m Mephisto optical upper limits
  18. GRB 250219A: SVOM/VT optical counterpart
  19. GRB 250219A: Swift-XRT observations
  20. GRB 250219A: Swift ToO observations
  21. GRB 250219A: SVOM detection of a burst
  22. Konus-Wind detection of GRB 250215A / EP250215a
  23. GRB 250217C: Swift-XRT observations
  24. SVOM/sb25021804: QSO variability in Liverpool Telescope observations
  25. GRB 250217C: COLIBRÍ/DDRAGO Upper Limits on the Optical Counterpart
  26. GRB 250217C: DDOTI Upper Limits on the Optical Afterglow
  27. GRB 250217C: Tiled Swift observations
  28. GRB 250215A / EP250215A: Encouraging Follow-up Observations of a BdHN I with a Rest-Frame Duration 2.3 s at z=4.61
  29. IPN triangulation of GRB 250217C (short)
  30. Transient SVOM/sb25021804: COLIBRÍ/DDRAGO Optical Upper Limits on the Optical Counterpart
  31. SVOM/sb25021804: SVOM detection of a long X-ray transient
  32. GRB 250213A: Swift-XRT observations
  33. GRB 250216A: AstroSat CZTI detection
  34. GRB 250217C: AstroSat CZTI detection of a short burst
  35. GRB 250217C: Fermi GBM Final Real-time Localization
  36. GRANDMA/OPD observations of GRB250215A
  37. GRB 250217B: Fermi GBM Final Real-time Localization
  38. GRB 250217A: Fermi GBM Final Real-time Localization
  39. GRB 250215A / EP250215a: LCO detection of the afterglow
  40. GRB 250216A: Fermi GBM Final Real-time Localization
  41. GRB 250215A: Swift/UVOT Upper Limits
  42. GRB 250215A: COLIBRÍ/DDRAGO Optical Upper Limits on the Afterglow
  43. EP250215a / GRB 250215A : GTC redshift z = 4.61
  44. GRB 250215A: Fermi GBM Observation
  45. EP250215a / GRB 250215A : NOT optical observations
  46. GRB 250215A/EP250215a: 1.6m Mephisto optical observation report
  47. GRB 250215A / EP250215a: Gemini-South optical observation of a likely rebrightening
  48. GRB 250213A: COLIBRÍ/DDRAGO Optical Upper Limits on the Afterglow
  49. GRB 250215A: Swift-XRT refined Analysis
  50. EP250215a / GRB 250215A: AstroSat CZTI detection
  51. EP250215A/GRB 250215A: INTEGRAL SPI-ACS detection
  52. EP250215a: EP-WXT detection and FXT follow-up observation of an X-ray transient
  53. GRB 250215A: Fermi GBM Final Real-time Localization
  54. EP250207b: Xinglong optical upper limit
  55. GRB 250213A: Swift ToO observations
  56. GRB 250214A: Fermi GBM Final Real-time Localization
  57. EP250212a: Xinglong optical upper limit
  58. GRB 250213A: SVOM detection of a burst
  59. GRB 250205A: VIRT Optical Upper Limit
  60. GRB 250205A: Leavitt Observatory optical upper limit
  61. GRB 250210A: GRBAlpha detection
  62. EP250207B: Chandra localization of the X-ray counterpart
  63. LIGO/Virgo/KAGRA S250206dm: FTW observations of counterpart candidates AT2025bbo and AT2025bcx, and of NED galaxies
  64. EP250212a: Liverpool Telescope optical upper limits
  65. EP250212a: EP-WXT detection and FXT follow-up observation of a fast X-ray transient
  66. GRB 250211A: Swift ToO observations
  67. GRB 250212A: Fermi GBM Final Real-time Localization
  68. GRB 250205A / EP250205A: radio detection with the VLA
  69. IceCube-250207A: One candidate from the Zwicky Transient Facility
  70. LIGO/Virgo/KAGRA S250206dm: Kinder confirmation of a possible artefact in AT 2025bbo
  71. Konus-Wind detection of GRB 250207A
  72. Konus-Wind detection of GRB 250206A
  73. EP250207b: Liverpool Telescope possible optical counterpart
  74. Gemini-South spectroscopic redshift of EP250207b host galaxy candidate (z=0.082)
  75. GRB 250207A: Skynet optical afterglow observations
  76. LIGO/Virgo/KAGRA S250206dm: Gemini-North spectroscopic observation of AT2025bbo and its host galaxy
  77. GRB 241128A: VIRT Optical Upper Limit
  78. GRB 250210A: INTEGRAL SPI-ACS detection
  79. GRB 250210A: AstroSat CZTI detection
  80. EP250207b: a new X-ray transient detected by Einstein Probe
  81. LIGO/Virgo/KAGRA S250206dm: MASTER detection AT2025bbo
  82. GRB 250209A: MAXI/GSC detection (possible detection of an X-ray flare from 1RXS J145110.3+310648)
  83. GRB 250210A: Fermi GBM Final Real-time Localization
  84. LIGO/Virgo/KAGRA S250206dm: Upper limits from GECAM Observations
  85. GRB 250204B: GRBAlpha detection
  86. GRB 250204A: GRBAlpha detection
  87. GRB 250207A: 1.3m DFOT Optical observations
  88. LIGO/Virgo/KAGRA S250206dm: WFST follow-up observations
  89. GRB 250206A: Swift-XRT observations
  90. LIGO/Virgo/KAGRA S250206dm: FRB 20250206A BOOTES-5 and 2.2m CAHA optical upper limits
  91. GRB 250129A: GRANDMA Continued Afterglow Detection
  92. LIGO/Virgo/KAGRA S250206dm: further Pan-STARRS observations and one candidate AT2025bbo
  93. GRB 250205A: 1.3m DFOT optical upper limit
  94. GRB 250206A: Tiled Swift observations
  95. GRB 250206A: EIRSAT-1 GMOD Detection
  96. GRB 250206A: Fermi-LAT detection
  97. GRB 250207B: Swift-XRT observations
  98. LIGO/Virgo/KAGRA S250206dm: Candidates from the Zwicky Transient Facility
  99. GRB 250208A: Fermi GBM Final Real-time Localization
  100. EP250207a: EP-WXT detection and XRT follow-up observation

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