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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"

28103 results found.

  1. GRB 250309B: Swift-XRT refined Analysis
  2. GRB 250309B / AT2025dws: OSIRIS+/GTC spectroscopy z=1.898
  3. Liverpool Telecope observations of AT 2025dws / GRB 250309B
  4. GRB 250309B / AT2025dws: SAO RAS optical observations
  5. GRB 250309B / AT2025dws: Swift-UVOT detection
  6. AT 2025dws, likely optical counterpart of GRB 250309B: LCO confirmation of fast fading
  7. GRB250309B: One candidate counterpart from the Zwicky Transient Facility
  8. IceCube-250309A: No candidates from the Zwicky Transient Facility
  9. Fermi-LAT gamma-ray observations of IceCube-250309A
  10. GRB 250308A: SVOM/GRM detection of QPO in the tail emission
  11. GRB 250309B: Fermi GBM Final Localization
  12. Correction to GCN 39633 - Swift is observing GRB 250309B/IceCube-250309A!
  13. GRB 230509B: Tiled Swift observations
  14. IceCube-250309A - IceCube observation of a high-energy neutrino candidate track-like event
  15. EP250308a: GSP optical upper limit
  16. EP250308a: Einstein Probe detection of an X-ray transient
  17. GRB 250309A: Fermi GBM Final Real-time Localization
  18. GRB 250306A: EIRSAT-1 GMOD detection
  19. Konus-Wind detection of GRB 250306A
  20. GRB 250307A: Fermi GBM Final Real-time Localization
  21. GRB 250306A: NuSTAR detection of the prompt emission
  22. EP250304a: MeerKAT detection of a possible radio counterpart
  23. GRB 250305A: AstroSat CZTI detection
  24. GRB 250306A: AstroSat CZTI detection
  25. GRB 250306A: Swift detection of a burst
  26. LIGO/Virgo/KAGRA S250306ej: Retraction of GW compact binary merger candidate
  27. GRB 250305A: Fermi GBM Final Real-time Localization
  28. GRB 250219A: SVOM/C-GFT optical upper limit at early phase
  29. EP 250304A: Optical counterpart detection by LCO
  30. EP250302A: 1.3m DFOT optical afterglow detection
  31. Konus-Wind detection of GRB 250222A
  32. EP250304a: REM NIR upper limits
  33. IPN triangulation of GRB 250222A
  34. EP250304a: Swift/UVOT detection of an optical counterpart with a rising light curve
  35. EP250304a: Swift-XRT detection of a fading X-ray source
  36. EP250304a: TRT optical counterpart detection
  37. EP250304a: Einstein Probe detection of an X-ray transient
  38. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: Swift/UVOT Upper Limits
  39. EP250225a: the candidate optical counterpart is an AGN
  40. EP250302a: Swift/UVOT detection
  41. EP250302a: NUTTelA-TAO Early Measurments
  42. EP250302a: REM NIR upper limits
  43. EP250302a: Xinglong F60B optical observation
  44. EP250302a: Swift-XRT observations of a fading X-ray source
  45. EP250302a: Einstein Probe detection of an X-ray transient
  46. GRB 250226A: GRANDMA Optical Observations
  47. EP250302a: Montarrenti Observatory optical detection
  48. EP250302a: FTW optical and NIR detection
  49. EP250302a: Nanshan/HMT optical counterpart detection
  50. IceCube-250302A - IceCube observation of a high-energy neutrino candidate track-like event
  51. GRB 250302A: Fermi GBM Final Real-time Localization
  52. GRB 250228A: Fermi GBM Final Localization
  53. GRB 250225B: VLT near-infrared afterglow confirmation
  54. EP250228a: Optical observations with Kinder and Swift/UVOT
  55. Konus-Wind detection of GRB 250226A
  56. GRB 250225B: EIRSAT-1 GMOD Detection
  57. GRB 250225B: VLT/HAWKI near-infrared observations
  58. EP250227a: Optical upper limits with Kinder observations
  59. EP250227a: Einstein Probe detected of a fast X-ray transient
  60. EP250228a: updates on the EP observations
  61. EP250225a: EP-FXT follow-up observation
  62. EP250223a: J band upper limit by SYSU 80cm telescope
  63. EP250228a: Swift/XRT localisation
  64. EP250228a: Einstein Probe detection of an X-ray transient
  65. GRB 250226A / EP250226a: LCO detection of the afterglow
  66. GRB 250226B: INTEGRAL SPI-ACS and PICsIT detection
  67. EP250226a/GRB 250226A: INTEGRAL SPI-ACS and PICsIT detection
  68. GRB 250225B: INTEGRAL SPI-ACS detection
  69. EP250226a / GRB 250226A: SVOM/VT optical observations
  70. EP250225a: TRT optical upper limits
  71. LIGO/Virgo/KAGRA S250206dm: Upper limits from SVOM/GRM Observations
  72. LIGO/Virgo/KAGRA S250223dk: Insight-HXMT/HE sub-threshold detection of a burst (HEB 250223501)
  73. LIGO/Virgo/KAGRA S250227y: Retraction of GW compact binary merger candidate
  74. GRB 250226B: Fermi GBM Final Real-time Localization
  75. GRB 250221A: ATCA Detections and Upper Limits
  76. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: Updated Sky localization and Coincidence with External Event
  77. Konus-Wind detection of GRB 250225B
  78. LIGO/Virgo/KAGRA S250223dk: DECam optical detections of Swift X-ray sources
  79. GRB 250225B: VLT optical and near-infrared candidate counterpart
  80. GRB 250225B: VLT/FORS2 candidate optical afterglow
  81. GRB 250226A: GECAM-B detection
  82. GRB 250221A: EP-FXT detection of the X-ray afterglow
  83. EP250226a/GRB 250226A: GSP detects optical counterpart
  84. EP250226a/GRB 250226A: COLIBRÍ/DDRAGO Detection of the Optical Counterpart
  85. EP250226a / GRB 250226A: VLT/X-shooter redshift of z = 3.315
  86. LIGO/Virgo S250223dk: Swift XRT observations, 7 X-ray sources
  87. EP250226a/GRB 250226A: EP-WXT detection and FXT follow-up observation of an X-ray transient
  88. GRB 250226A: Fermi GBM Final Real-time Localization
  89. EP250225a: GSP optical upper limit
  90. EP250225a: Einstein Probe detected of a fast X-ray transient
  91. GRB 250225B: Swift detection of a burst
  92. EP250223a: GROWTH-India Telescope optical observations
  93. EP250215A: J band upper limit by SYSU 80cm telescope
  94. GRB 250225A: Fermi GBM Final Real-time Localization
  95. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: AstroSat CZTI non-detection and upper limits
  96. GRB 250207a: ATCA Radio Upper Limits
  97. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: Upper limits from Fermi-GBM Observations
  98. GRB 250119B: VZLUSAT-2 detection
  99. GRB 250223C: Fermi GBM Final Real-time Localization
  100. GRB 250202B: VZLUSAT-2 detection

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