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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 250225B: Fermi GBM Observation
  2. GRB 250221A: ATCA Detections and Upper Limits
  3. GRB 250225B: REM NIR upper limits
  4. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: Updated Sky localization and Coincidence with External Event
  5. Konus-Wind detection of GRB 250225B
  6. LIGO/Virgo/KAGRA S250223dk: DECam optical detections of Swift X-ray sources
  7. EP250223a: CrAO ZTSH optical observation
  8. GRB 250225B: VLT optical and near-infrared candidate counterpart
  9. GRB 250225B: VLT/FORS2 candidate optical afterglow
  10. GRB 250225B: SVOM/GRM observation of a long burst
  11. GRB 250226A: GECAM-B detection
  12. GRB 250221A: EP-FXT detection of the X-ray afterglow
  13. GRB 250214A: SVOM/GRM observation
  14. EP250226a/GRB 250226A: GSP detects optical counterpart
  15. EP250226a/GRB 250226A: COLIBRÍ/DDRAGO Detection of the Optical Counterpart
  16. EP250226a / GRB 250226A: VLT/X-shooter redshift of z = 3.315
  17. EP250226a / GRB 250226A: TRT optical counterpart observation
  18. LIGO/Virgo S250223dk: Swift XRT observations, 7 X-ray sources
  19. EP250226a: Global MASTER-Net observations report
  20. Swift GRB 250225B: Global MASTER-Net observations report
  21. EP250226a/GRB 250226A: EP-WXT detection and FXT follow-up observation of an X-ray transient
  22. Fermi GRB 250226A: Global MASTER-Net observations report
  23. Fermi trigger No 762205158: Global MASTER-Net observations report
  24. GRB 250226A: Fermi GBM Final Real-time Localization
  25. EP250225a: Global MASTER-Net observations report
  26. EP250225a: GSP optical upper limit
  27. EP250223a: GMG Optical Observation
  28. EP250225a: Einstein Probe detected of a fast X-ray transient
  29. Fermi GRB 250225A: Global MASTER-Net observations report
  30. GRB 250225B: Swift detection of a burst
  31. EP250223a: GROWTH-India Telescope optical observations
  32. GRB 250221A: Swift-BAT refined analysis
  33. GRB 250223C: SVOM/GRM observation of a long burst
  34. EP250215A: J band upper limit by SYSU 80cm telescope
  35. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: DECam GW-MMADS candidates
  36. GRB 250225A: Fermi GBM Final Real-time Localization
  37. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: AstroSat CZTI non-detection and upper limits
  38. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: Magellan upper limits.
  39. EP250223a: Kinder optical follow-up observations
  40. GRB 250207a: ATCA Radio Upper Limits
  41. LIGO/Virgo/KAGRA S250223dk: DECam DESGW Candidates
  42. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: Upper limits from Fermi-GBM Observations
  43. GRB 250119B: VZLUSAT-2 detection
  44. GRB 250223C: Fermi GBM Final Real-time Localization
  45. GOTO observations of LVK S250223dk/Swift-BAT RAVEN alert
  46. GRB 250202B: VZLUSAT-2 detection
  47. GRB 250219A: EP-FXT afterglow detection
  48. EP250223a: GOTO optical afterglow detections
  49. GRB 250222A: SVOM/GRM observation of a burst
  50. EP250223a: COLIBRÍ/DDRAGO Detection of the Optical Counterpart and Slow Fading
  51. GRB 250210A: VZLUSAT-2 detection
  52. GRB 250206A: VZLUSAT-2 detection
  53. EP250223a: REM NIR upper limit
  54. EP250223a: TRT optical afterglow observation
  55. EP250223a: refined analysis of the EP-WXT and FXT observations
  56. EP250223a: 1.6m Mephisto and 50cm array observations
  57. GRB 250221A: TNOT detection of the optical counterpart
  58. EP250223a: SVOM/VT optical observation
  59. LIGO/Virgo/KAGRA S250223dk: DDOTI Upper Limits on the Optical Counterpart
  60. 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
  61. The EP-WXT trigger 01709131882 is likely a flaring star
  62. EP250223a: OASDG optical observations
  63. EP250223a: LCO detection of the afterglow
  64. EP250223a: early optical detection by BOOTES-4
  65. EP250223a: NOT redshift z = 2.756
  66. EP250223a: Swift/XRT localization
  67. EP250223a: NOT optical afterglow candidate
  68. GRB 250223B: Fermi GBM Final Localization
  69. EP250223a: Global MASTER-Net observations report
  70. GRB 250221A: VLA radio detection
  71. Fermi GRB 250223A: Global MASTER-Net observations report
  72. Fermi trigger No 762020305: Global MASTER-Net observations report
  73. GRB 250223A: Fermi GBM Final Real-time Localization
  74. EP250223a: Einstein Probe detection of an X-ray transient
  75. LIGO/Virgo/KAGRA S250206dm: Upper limits from IceCube neutrino searches
  76. GRB 250221A: continued Assy optical observations, brightening afterglow confirmation
  77. GRB 250221A: continued Mondy optical observations, brightening afterglow
  78. GRB 250221A: Optical counterpart detection by LCO.
  79. GRB 250221A: Mondy optical observations
  80. Konus-Wind detection of GRB 250221A
  81. GRB 250221A: Assy optical observations
  82. EP250220a: FTW optical and NIR observations and upper limits
  83. EP250220a: EP-FXT follow-up observations
  84. GRB 250219A: NUTTelA-TAO / BSTI Optical Limits
  85. GRB 250221A: VLT/X-shooter redshift z = 0.768
  86. GRB 250221A: GRANDMA/TAROT Detection
  87. Fermi trigger No 761805304: Global MASTER-Net observations report
  88. Fermi Gamma-ray Burst Monitor trigger 761867337/250221909 is not a GRB
  89. GRB 250221A: Swift-XRT refined Analysis
  90. GRB 250221A: NOT optical observations
  91. GRB 250221A: 1.6m Mephisto optical detection
  92. LIGO/Virgo/KAGRA S250221gb: Retraction of GW compact binary merger candidate
  93. GRB 250221A: AKO Optical Upper Limit
  94. GRB 250221A: Swift/UVOT Detection
  95. EP250220a: Liverpool Telescope upper limits
  96. GRB 250219A: GRANDMA/Kilonova-Catcher upper limits
  97. GRB 250221A: REM optical/NIR afterglow detection
  98. IceCube-250207A: MASTER flaring blazar QSOJ0854+2006 with Zhirkov effect
  99. GRB 250221A: Enhanced Swift-XRT position
  100. LIGO/Virgo/KAGRA S250221eb: Retraction of GW compact binary merger candidate

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