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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. LIGO/Virgo/KAGRA S250227e: Identification of a GW compact binary merger candidate
  2. Fermi GRB 250226B: Global MASTER-Net observations report
  3. LIGO/Virgo/KAGRA S250226dl: Identification of a GW compact binary merger candidate
  4. GRB 250226B: Fermi GBM Final Real-time Localization
  5. GRB 250225B: Fermi GBM Observation
  6. GRB 250221A: ATCA Detections and Upper Limits
  7. GRB 250225B: REM NIR upper limits
  8. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: Updated Sky localization and Coincidence with External Event
  9. Konus-Wind detection of GRB 250225B
  10. LIGO/Virgo/KAGRA S250223dk: DECam optical detections of Swift X-ray sources
  11. EP250223a: CrAO ZTSH optical observation
  12. GRB 250225B: VLT optical and near-infrared candidate counterpart
  13. GRB 250225B: VLT/FORS2 candidate optical afterglow
  14. GRB 250225B: SVOM/GRM observation of a long burst
  15. GRB 250226A: GECAM-B detection
  16. GRB 250221A: EP-FXT detection of the X-ray afterglow
  17. GRB 250214A: SVOM/GRM observation
  18. EP250226a/GRB 250226A: GSP detects optical counterpart
  19. EP250226a/GRB 250226A: COLIBRÍ/DDRAGO Detection of the Optical Counterpart
  20. EP250226a / GRB 250226A: VLT/X-shooter redshift of z = 3.315
  21. EP250226a / GRB 250226A: TRT optical counterpart observation
  22. LIGO/Virgo S250223dk: Swift XRT observations, 7 X-ray sources
  23. EP250226a: Global MASTER-Net observations report
  24. Swift GRB 250225B: Global MASTER-Net observations report
  25. EP250226a/GRB 250226A: EP-WXT detection and FXT follow-up observation of an X-ray transient
  26. Fermi GRB 250226A: Global MASTER-Net observations report
  27. Fermi trigger No 762205158: Global MASTER-Net observations report
  28. GRB 250226A: Fermi GBM Final Real-time Localization
  29. EP250225a: Global MASTER-Net observations report
  30. EP250225a: GSP optical upper limit
  31. EP250223a: GMG Optical Observation
  32. EP250225a: Einstein Probe detected of a fast X-ray transient
  33. Fermi GRB 250225A: Global MASTER-Net observations report
  34. GRB 250225B: Swift detection of a burst
  35. EP250223a: GROWTH-India Telescope optical observations
  36. GRB 250221A: Swift-BAT refined analysis
  37. GRB 250223C: SVOM/GRM observation of a long burst
  38. EP250215A: J band upper limit by SYSU 80cm telescope
  39. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: DECam GW-MMADS candidates
  40. GRB 250225A: Fermi GBM Final Real-time Localization
  41. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: AstroSat CZTI non-detection and upper limits
  42. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: Magellan upper limits.
  43. EP250223a: Kinder optical follow-up observations
  44. GRB 250207a: ATCA Radio Upper Limits
  45. LIGO/Virgo/KAGRA S250223dk: DECam DESGW Candidates
  46. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: Upper limits from Fermi-GBM Observations
  47. GRB 250119B: VZLUSAT-2 detection
  48. GRB 250223C: Fermi GBM Final Real-time Localization
  49. GOTO observations of LVK S250223dk/Swift-BAT RAVEN alert
  50. GRB 250202B: VZLUSAT-2 detection
  51. GRB 250219A: EP-FXT afterglow detection
  52. EP250223a: GOTO optical afterglow detections
  53. GRB 250222A: SVOM/GRM observation of a burst
  54. EP250223a: COLIBRÍ/DDRAGO Detection of the Optical Counterpart and Slow Fading
  55. GRB 250210A: VZLUSAT-2 detection
  56. GRB 250206A: VZLUSAT-2 detection
  57. EP250223a: REM NIR upper limit
  58. EP250223a: TRT optical afterglow observation
  59. EP250223a: refined analysis of the EP-WXT and FXT observations
  60. EP250223a: 1.6m Mephisto and 50cm array observations
  61. GRB 250221A: TNOT detection of the optical counterpart
  62. EP250223a: SVOM/VT optical observation
  63. LIGO/Virgo/KAGRA S250223dk: DDOTI Upper Limits on the Optical Counterpart
  64. 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
  65. The EP-WXT trigger 01709131882 is likely a flaring star
  66. EP250223a: OASDG optical observations
  67. EP250223a: LCO detection of the afterglow
  68. EP250223a: early optical detection by BOOTES-4
  69. EP250223a: NOT redshift z = 2.756
  70. EP250223a: Swift/XRT localization
  71. EP250223a: NOT optical afterglow candidate
  72. GRB 250223B: Fermi GBM Final Localization
  73. EP250223a: Global MASTER-Net observations report
  74. GRB 250221A: VLA radio detection
  75. Fermi GRB 250223A: Global MASTER-Net observations report
  76. Fermi trigger No 762020305: Global MASTER-Net observations report
  77. GRB 250223A: Fermi GBM Final Real-time Localization
  78. EP250223a: Einstein Probe detection of an X-ray transient
  79. LIGO/Virgo/KAGRA S250206dm: Upper limits from IceCube neutrino searches
  80. GRB 250221A: continued Assy optical observations, brightening afterglow confirmation
  81. GRB 250221A: continued Mondy optical observations, brightening afterglow
  82. GRB 250221A: Optical counterpart detection by LCO.
  83. GRB 250221A: Mondy optical observations
  84. Konus-Wind detection of GRB 250221A
  85. GRB 250221A: Assy optical observations
  86. EP250220a: FTW optical and NIR observations and upper limits
  87. EP250220a: EP-FXT follow-up observations
  88. GRB 250219A: NUTTelA-TAO / BSTI Optical Limits
  89. GRB 250221A: VLT/X-shooter redshift z = 0.768
  90. GRB 250221A: GRANDMA/TAROT Detection
  91. Fermi trigger No 761805304: Global MASTER-Net observations report
  92. Fermi Gamma-ray Burst Monitor trigger 761867337/250221909 is not a GRB
  93. GRB 250221A: Swift-XRT refined Analysis
  94. GRB 250221A: NOT optical observations
  95. GRB 250221A: 1.6m Mephisto optical detection
  96. LIGO/Virgo/KAGRA S250221gb: Retraction of GW compact binary merger candidate
  97. GRB 250221A: AKO Optical Upper Limit
  98. GRB 250221A: Swift/UVOT Detection
  99. EP250220a: Liverpool Telescope upper limits
  100. GRB 250219A: GRANDMA/Kilonova-Catcher upper limits

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