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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 250225A: Fermi GBM Final Real-time Localization
  2. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: AstroSat CZTI non-detection and upper limits
  3. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: Magellan upper limits.
  4. EP250223a: Kinder optical follow-up observations
  5. GRB 250207a: ATCA Radio Upper Limits
  6. LIGO/Virgo/KAGRA S250223dk: DECam DESGW Candidates
  7. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: Upper limits from Fermi-GBM Observations
  8. GRB 250119B: VZLUSAT-2 detection
  9. GRB 250223C: Fermi GBM Final Real-time Localization
  10. GOTO observations of LVK S250223dk/Swift-BAT RAVEN alert
  11. GRB 250202B: VZLUSAT-2 detection
  12. GRB 250219A: EP-FXT afterglow detection
  13. EP250223a: GOTO optical afterglow detections
  14. GRB 250222A: SVOM/GRM observation of a burst
  15. EP250223a: COLIBRÍ/DDRAGO Detection of the Optical Counterpart and Slow Fading
  16. GRB 250210A: VZLUSAT-2 detection
  17. GRB 250206A: VZLUSAT-2 detection
  18. EP250223a: REM NIR upper limit
  19. EP250223a: TRT optical afterglow observation
  20. EP250223a: refined analysis of the EP-WXT and FXT observations
  21. EP250223a: 1.6m Mephisto and 50cm array observations
  22. GRB 250221A: TNOT detection of the optical counterpart
  23. EP250223a: SVOM/VT optical observation
  24. LIGO/Virgo/KAGRA S250223dk: DDOTI Upper Limits on the Optical Counterpart
  25. 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
  26. The EP-WXT trigger 01709131882 is likely a flaring star
  27. EP250223a: OASDG optical observations
  28. EP250223a: LCO detection of the afterglow
  29. EP250223a: early optical detection by BOOTES-4
  30. EP250223a: NOT redshift z = 2.756
  31. EP250223a: Swift/XRT localization
  32. EP250223a: NOT optical afterglow candidate
  33. GRB 250223B: Fermi GBM Final Localization
  34. EP250223a: Global MASTER-Net observations report
  35. GRB 250221A: VLA radio detection
  36. Fermi GRB 250223A: Global MASTER-Net observations report
  37. Fermi trigger No 762020305: Global MASTER-Net observations report
  38. GRB 250223A: Fermi GBM Final Real-time Localization
  39. EP250223a: Einstein Probe detection of an X-ray transient
  40. LIGO/Virgo/KAGRA S250206dm: Upper limits from IceCube neutrino searches
  41. GRB 250221A: continued Assy optical observations, brightening afterglow confirmation
  42. GRB 250221A: continued Mondy optical observations, brightening afterglow
  43. GRB 250221A: Optical counterpart detection by LCO.
  44. GRB 250221A: Mondy optical observations
  45. Konus-Wind detection of GRB 250221A
  46. GRB 250221A: Assy optical observations
  47. EP250220a: FTW optical and NIR observations and upper limits
  48. EP250220a: EP-FXT follow-up observations
  49. GRB 250219A: NUTTelA-TAO / BSTI Optical Limits
  50. GRB 250221A: VLT/X-shooter redshift z = 0.768
  51. GRB 250221A: GRANDMA/TAROT Detection
  52. Fermi trigger No 761805304: Global MASTER-Net observations report
  53. Fermi Gamma-ray Burst Monitor trigger 761867337/250221909 is not a GRB
  54. GRB 250221A: Swift-XRT refined Analysis
  55. GRB 250221A: NOT optical observations
  56. GRB 250221A: 1.6m Mephisto optical detection
  57. LIGO/Virgo/KAGRA S250221gb: Retraction of GW compact binary merger candidate
  58. GRB 250221A: AKO Optical Upper Limit
  59. GRB 250221A: Swift/UVOT Detection
  60. EP250220a: Liverpool Telescope upper limits
  61. GRB 250219A: GRANDMA/Kilonova-Catcher upper limits
  62. GRB 250221A: REM optical/NIR afterglow detection
  63. IceCube-250207A: MASTER flaring blazar QSOJ0854+2006 with Zhirkov effect
  64. GRB 250221A: Enhanced Swift-XRT position
  65. LIGO/Virgo/KAGRA S250221eb: Retraction of GW compact binary merger candidate
  66. EP250220a: 1.6m Mephisto observations
  67. EP250220a: Liverpool Telescope optical upper limits
  68. EP250220a: Optical upper limit with Kinder observations
  69. SVOM trigger sb25022102 is not an astrophysical event
  70. SVOM/sb25022102: SVOM detection of an X-ray transient
  71. GRB 250221A: COLIBRÍ/DDRAGO Confirmation of a Bright Optical Counterpart
  72. GRB 250221A: Swift detection of a burst with an optical counterpart
  73. Swift GRB250221.15: Global MASTER-Net OT detection
  74. Swift GRB250221.15: Global MASTER-Net observations report
  75. EP250220a: Xinglong optical upper limit
  76. Fermi Gamma-ray Burst Monitor trigger 761788229/250220993 is not a GRB
  77. GRB 250220B: Fermi GBM Final Real-time Localization
  78. Fermi Gamma-ray Burst Monitor trigger 761782146/250220923 is not a GRB
  79. GRB 250220A: Fermi GBM Final Real-time Localization
  80. EP250220a: Global MASTER-Net observations report
  81. EP250220a: EP-WXT detection of a fast X-ray transient
  82. Konus-Wind detection of GRB 250217C (short)
  83. GRB 250219A: Swift/UVOT Upper Limits
  84. GRB 250219A: OHP/T193 optical upper limit
  85. GRB 250219A: NOT optical observations
  86. GRB 250219A: COLIBRÍ/DDRAGO Detection of the Optical Counterpart
  87. GRB 250219A: 1.6m Mephisto optical upper limits
  88. GRB 250219A: SVOM/VT optical counterpart
  89. GRB 250219A: Swift-XRT observations
  90. LIGO/Virgo/KAGRA S250206dm: Upper limits from MSU cubesats observations
  91. GRB 250219A: Swift ToO observations
  92. GRB 250219A: SVOM detection of a burst
  93. Konus-Wind detection of GRB 250215A / EP250215a
  94. SVOM/sb25021804: COLIBRÍ/DDRAGO Confirmation of Variability
  95. GRB 250217C: Swift-XRT observations
  96. SVOM/sb25021804: QSO variability in Liverpool Telescope observations
  97. GRB 250217C: COLIBRÍ/DDRAGO Upper Limits on the Optical Counterpart
  98. GRB 250217C: DDOTI Upper Limits on the Optical Afterglow
  99. GRB 250217C: SVOM/GRM observation
  100. GRB 250217C: Tiled Swift observations

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