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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. EP250226a / GRB 250226A: TRT optical counterpart observation
  2. LIGO/Virgo S250223dk: Swift XRT observations, 7 X-ray sources
  3. EP250226a: Global MASTER-Net observations report
  4. Swift GRB 250225B: Global MASTER-Net observations report
  5. EP250226a/GRB 250226A: EP-WXT detection and FXT follow-up observation of an X-ray transient
  6. Fermi GRB 250226A: Global MASTER-Net observations report
  7. Fermi trigger No 762205158: Global MASTER-Net observations report
  8. GRB 250226A: Fermi GBM Final Real-time Localization
  9. EP250225a: Global MASTER-Net observations report
  10. EP250225a: GSP optical upper limit
  11. EP250223a: GMG Optical Observation
  12. EP250225a: Einstein Probe detected of a fast X-ray transient
  13. Fermi GRB 250225A: Global MASTER-Net observations report
  14. GRB 250225B: Swift detection of a burst
  15. EP250223a: GROWTH-India Telescope optical observations
  16. GRB 250221A: Swift-BAT refined analysis
  17. GRB 250223C: SVOM/GRM observation of a long burst
  18. EP250215A: J band upper limit by SYSU 80cm telescope
  19. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: DECam GW-MMADS candidates
  20. GRB 250225A: Fermi GBM Final Real-time Localization
  21. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: AstroSat CZTI non-detection and upper limits
  22. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: Magellan upper limits.
  23. EP250223a: Kinder optical follow-up observations
  24. GRB 250207a: ATCA Radio Upper Limits
  25. LIGO/Virgo/KAGRA S250223dk: DECam DESGW Candidates
  26. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: Upper limits from Fermi-GBM Observations
  27. GRB 250119B: VZLUSAT-2 detection
  28. GRB 250223C: Fermi GBM Final Real-time Localization
  29. GOTO observations of LVK S250223dk/Swift-BAT RAVEN alert
  30. GRB 250202B: VZLUSAT-2 detection
  31. GRB 250219A: EP-FXT afterglow detection
  32. EP250223a: GOTO optical afterglow detections
  33. GRB 250222A: SVOM/GRM observation of a burst
  34. EP250223a: COLIBRÍ/DDRAGO Detection of the Optical Counterpart and Slow Fading
  35. GRB 250210A: VZLUSAT-2 detection
  36. GRB 250206A: VZLUSAT-2 detection
  37. EP250223a: REM NIR upper limit
  38. EP250223a: TRT optical afterglow observation
  39. EP250223a: refined analysis of the EP-WXT and FXT observations
  40. EP250223a: 1.6m Mephisto and 50cm array observations
  41. GRB 250221A: TNOT detection of the optical counterpart
  42. EP250223a: SVOM/VT optical observation
  43. LIGO/Virgo/KAGRA S250223dk: DDOTI Upper Limits on the Optical Counterpart
  44. 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
  45. The EP-WXT trigger 01709131882 is likely a flaring star
  46. EP250223a: OASDG optical observations
  47. EP250223a: LCO detection of the afterglow
  48. EP250223a: early optical detection by BOOTES-4
  49. EP250223a: NOT redshift z = 2.756
  50. EP250223a: Swift/XRT localization
  51. EP250223a: NOT optical afterglow candidate
  52. GRB 250223B: Fermi GBM Final Localization
  53. EP250223a: Global MASTER-Net observations report
  54. GRB 250221A: VLA radio detection
  55. Fermi GRB 250223A: Global MASTER-Net observations report
  56. Fermi trigger No 762020305: Global MASTER-Net observations report
  57. GRB 250223A: Fermi GBM Final Real-time Localization
  58. EP250223a: Einstein Probe detection of an X-ray transient
  59. LIGO/Virgo/KAGRA S250206dm: Upper limits from IceCube neutrino searches
  60. GRB 250221A: continued Assy optical observations, brightening afterglow confirmation
  61. GRB 250221A: continued Mondy optical observations, brightening afterglow
  62. GRB 250221A: Optical counterpart detection by LCO.
  63. GRB 250221A: Mondy optical observations
  64. Konus-Wind detection of GRB 250221A
  65. GRB 250221A: Assy optical observations
  66. EP250220a: FTW optical and NIR observations and upper limits
  67. EP250220a: EP-FXT follow-up observations
  68. GRB 250219A: NUTTelA-TAO / BSTI Optical Limits
  69. GRB 250221A: VLT/X-shooter redshift z = 0.768
  70. GRB 250221A: GRANDMA/TAROT Detection
  71. Fermi trigger No 761805304: Global MASTER-Net observations report
  72. Fermi Gamma-ray Burst Monitor trigger 761867337/250221909 is not a GRB
  73. GRB 250221A: Swift-XRT refined Analysis
  74. GRB 250221A: NOT optical observations
  75. GRB 250221A: 1.6m Mephisto optical detection
  76. LIGO/Virgo/KAGRA S250221gb: Retraction of GW compact binary merger candidate
  77. GRB 250221A: AKO Optical Upper Limit
  78. GRB 250221A: Swift/UVOT Detection
  79. EP250220a: Liverpool Telescope upper limits
  80. GRB 250219A: GRANDMA/Kilonova-Catcher upper limits
  81. GRB 250221A: REM optical/NIR afterglow detection
  82. IceCube-250207A: MASTER flaring blazar QSOJ0854+2006 with Zhirkov effect
  83. GRB 250221A: Enhanced Swift-XRT position
  84. LIGO/Virgo/KAGRA S250221eb: Retraction of GW compact binary merger candidate
  85. EP250220a: 1.6m Mephisto observations
  86. EP250220a: Liverpool Telescope optical upper limits
  87. EP250220a: Optical upper limit with Kinder observations
  88. SVOM trigger sb25022102 is not an astrophysical event
  89. SVOM/sb25022102: SVOM detection of an X-ray transient
  90. GRB 250221A: COLIBRÍ/DDRAGO Confirmation of a Bright Optical Counterpart
  91. GRB 250221A: Swift detection of a burst with an optical counterpart
  92. Swift GRB250221.15: Global MASTER-Net OT detection
  93. Swift GRB250221.15: Global MASTER-Net observations report
  94. EP250220a: Xinglong optical upper limit
  95. Fermi Gamma-ray Burst Monitor trigger 761788229/250220993 is not a GRB
  96. GRB 250220B: Fermi GBM Final Real-time Localization
  97. Fermi Gamma-ray Burst Monitor trigger 761782146/250220923 is not a GRB
  98. GRB 250220A: Fermi GBM Final Real-time Localization
  99. EP250220a: Global MASTER-Net observations report
  100. EP250220a: EP-WXT detection of a fast X-ray transient

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