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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. Fermi trigger No 762205158: Global MASTER-Net observations report
  2. GRB 250226A: Fermi GBM Final Real-time Localization
  3. EP250225a: Global MASTER-Net observations report
  4. EP250225a: GSP optical upper limit
  5. EP250223a: GMG Optical Observation
  6. EP250225a: Einstein Probe detected of a fast X-ray transient
  7. Fermi GRB 250225A: Global MASTER-Net observations report
  8. GRB 250225B: Swift detection of a burst
  9. EP250223a: GROWTH-India Telescope optical observations
  10. GRB 250221A: Swift-BAT refined analysis
  11. GRB 250223C: SVOM/GRM observation of a long burst
  12. EP250215A: J band upper limit by SYSU 80cm telescope
  13. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: DECam GW-MMADS candidates
  14. GRB 250225A: Fermi GBM Final Real-time Localization
  15. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: AstroSat CZTI non-detection and upper limits
  16. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: Magellan upper limits.
  17. EP250223a: Kinder optical follow-up observations
  18. GRB 250207a: ATCA Radio Upper Limits
  19. LIGO/Virgo/KAGRA S250223dk: DECam DESGW Candidates
  20. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: Upper limits from Fermi-GBM Observations
  21. GRB 250119B: VZLUSAT-2 detection
  22. GRB 250223C: Fermi GBM Final Real-time Localization
  23. GOTO observations of LVK S250223dk/Swift-BAT RAVEN alert
  24. GRB 250202B: VZLUSAT-2 detection
  25. GRB 250219A: EP-FXT afterglow detection
  26. EP250223a: GOTO optical afterglow detections
  27. GRB 250222A: SVOM/GRM observation of a burst
  28. EP250223a: COLIBRÍ/DDRAGO Detection of the Optical Counterpart and Slow Fading
  29. GRB 250210A: VZLUSAT-2 detection
  30. GRB 250206A: VZLUSAT-2 detection
  31. EP250223a: REM NIR upper limit
  32. EP250223a: TRT optical afterglow observation
  33. EP250223a: refined analysis of the EP-WXT and FXT observations
  34. EP250223a: 1.6m Mephisto and 50cm array observations
  35. GRB 250221A: TNOT detection of the optical counterpart
  36. EP250223a: SVOM/VT optical observation
  37. LIGO/Virgo/KAGRA S250223dk: DDOTI Upper Limits on the Optical Counterpart
  38. 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
  39. The EP-WXT trigger 01709131882 is likely a flaring star
  40. EP250223a: OASDG optical observations
  41. EP250223a: LCO detection of the afterglow
  42. EP250223a: early optical detection by BOOTES-4
  43. EP250223a: NOT redshift z = 2.756
  44. EP250223a: Swift/XRT localization
  45. EP250223a: NOT optical afterglow candidate
  46. GRB 250223B: Fermi GBM Final Localization
  47. EP250223a: Global MASTER-Net observations report
  48. GRB 250221A: VLA radio detection
  49. Fermi GRB 250223A: Global MASTER-Net observations report
  50. Fermi trigger No 762020305: Global MASTER-Net observations report
  51. GRB 250223A: Fermi GBM Final Real-time Localization
  52. EP250223a: Einstein Probe detection of an X-ray transient
  53. LIGO/Virgo/KAGRA S250206dm: Upper limits from IceCube neutrino searches
  54. GRB 250221A: continued Assy optical observations, brightening afterglow confirmation
  55. GRB 250221A: continued Mondy optical observations, brightening afterglow
  56. GRB 250221A: Optical counterpart detection by LCO.
  57. GRB 250221A: Mondy optical observations
  58. Konus-Wind detection of GRB 250221A
  59. GRB 250221A: Assy optical observations
  60. EP250220a: FTW optical and NIR observations and upper limits
  61. EP250220a: EP-FXT follow-up observations
  62. GRB 250219A: NUTTelA-TAO / BSTI Optical Limits
  63. GRB 250221A: VLT/X-shooter redshift z = 0.768
  64. GRB 250221A: GRANDMA/TAROT Detection
  65. Fermi trigger No 761805304: Global MASTER-Net observations report
  66. Fermi Gamma-ray Burst Monitor trigger 761867337/250221909 is not a GRB
  67. GRB 250221A: Swift-XRT refined Analysis
  68. GRB 250221A: NOT optical observations
  69. GRB 250221A: 1.6m Mephisto optical detection
  70. LIGO/Virgo/KAGRA S250221gb: Retraction of GW compact binary merger candidate
  71. GRB 250221A: AKO Optical Upper Limit
  72. GRB 250221A: Swift/UVOT Detection
  73. EP250220a: Liverpool Telescope upper limits
  74. GRB 250219A: GRANDMA/Kilonova-Catcher upper limits
  75. GRB 250221A: REM optical/NIR afterglow detection
  76. IceCube-250207A: MASTER flaring blazar QSOJ0854+2006 with Zhirkov effect
  77. GRB 250221A: Enhanced Swift-XRT position
  78. LIGO/Virgo/KAGRA S250221eb: Retraction of GW compact binary merger candidate
  79. EP250220a: 1.6m Mephisto observations
  80. EP250220a: Liverpool Telescope optical upper limits
  81. EP250220a: Optical upper limit with Kinder observations
  82. SVOM trigger sb25022102 is not an astrophysical event
  83. SVOM/sb25022102: SVOM detection of an X-ray transient
  84. GRB 250221A: COLIBRÍ/DDRAGO Confirmation of a Bright Optical Counterpart
  85. GRB 250221A: Swift detection of a burst with an optical counterpart
  86. Swift GRB250221.15: Global MASTER-Net OT detection
  87. Swift GRB250221.15: Global MASTER-Net observations report
  88. EP250220a: Xinglong optical upper limit
  89. Fermi Gamma-ray Burst Monitor trigger 761788229/250220993 is not a GRB
  90. GRB 250220B: Fermi GBM Final Real-time Localization
  91. Fermi Gamma-ray Burst Monitor trigger 761782146/250220923 is not a GRB
  92. GRB 250220A: Fermi GBM Final Real-time Localization
  93. EP250220a: Global MASTER-Net observations report
  94. EP250220a: EP-WXT detection of a fast X-ray transient
  95. Konus-Wind detection of GRB 250217C (short)
  96. GRB 250219A: Swift/UVOT Upper Limits
  97. GRB 250219A: OHP/T193 optical upper limit
  98. GRB 250219A: NOT optical observations
  99. GRB 250219A: COLIBRÍ/DDRAGO Detection of the Optical Counterpart
  100. GRB 250219A: 1.6m Mephisto optical upper limits

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