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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"

28076 results found.

  1. GRB 250317B: GTC/OSIRIS+ spectroscopic redshift z=3.44
  2. GRB 250317C: GECAM-B detection
  3. GRB250312A: Swift/UVOT Upper Limits
  4. GRB 250317B: REM optical/NIR observations
  5. GRB 250317B: Swift-XRT observations
  6. GRB 250316A: Swift/UVOT Upper Limits
  7. GRB 250314A: REM optical/NIR upper limits
  8. GRB 250316A: AbAO AS-32 Optical Upper Limit
  9. EP 250317B: Fading optical counterpart detection by LCO
  10. GRB 250316A: Swift-XRT afterglow detection
  11. GRB 250317B: LCO detection of the fading optical afterglow
  12. GRB 250317B: refined SVOM/MXT analysis
  13. GRB 250317B: SVOM/VT detection of an optical candidate from VHF data
  14. GRB 250317B: SVOM/F-GFT (COLIBRÍ) Detection of a Fading Optical Counterpart
  15. GRB 250317B: SVOM detection of a burst / correction to GRB name of GCN 39752
  16. GRB 250317B: SVOM detection of a burst
  17. GRB 250316A: Swift-XRT observations
  18. GRB 250317A: Fermi GBM Final Real-time Localization
  19. GRB 250316A: Swift ToO observations
  20. GRB 250316A: Swift/BAT-GUANO arcminute localization of a burst
  21. GRB 250314A: GTC z-band upper limit and updated photo-z ~ 7.27
  22. GRB 250316A: Fermi GBM Final Real-time Localization
  23. GRB 250315A/EP250315A: Fermi-GBM Sub-Threshold Detection
  24. GRB 250314A: EP-FXT afterglow detection
  25. GRB 250314A: Swift/UVOT Upper Limits
  26. GRB 250312B: GRBAlpha detection
  27. GRB 250313.89 / Fermi trigger 763594063: bright OT AT 2025ehi detection
  28. GRB 250314A: Swift XRT Detection
  29. EP250315a: Einstein Probe detection of an X-ray transient
  30. SVOM/MXT upper limit on GRB 250314A
  31. GRB 250314A: SVOM/VT upper limit
  32. GRB 250314A: NOT near-infrared candidate counterpart
  33. GRB 250313A: Fermi GBM Detection
  34. GRB 250313A: CALET Gamma-Ray Burst Monitor detection
  35. GRB 250313A: Swift-XRT observations
  36. Konus-Wind detection of GRB 250313A
  37. Konus-Wind detection of GRB 250308A
  38. GRB 250314A: SVOM detection of a burst
  39. EP250311a/GRB 250311A: Correction to EP-WXT detection time
  40. FRB 20250206A: Nondetection of Repeating Bursts from FRB 20250206A with FAST
  41. GRB 250313A: AstroSat CZTI detection of a bright long burst
  42. IceCube-250309A: MASTER detection of J140105.33-091631.6 blazar flare with Zhirkov effect
  43. GRB 250313A: Fermi-LAT detection
  44. GRB 250313A: Swift ToO observations
  45. EP250304a: Pan-STARRS r and i-band imaging and photometry
  46. GRB 250309B: PRIME near-infrared upper limits in 2nd epoch
  47. GRB 250313A: Fermi GBM Final Real-time Localization
  48. EP250304a: SVOM/VT optical observation
  49. EP250311a/GRB 250311A: EP-FXT follow-up observation
  50. ATCA detection of the radio counterpart of GRB 250309B-AT2025dws
  51. EP250302a: Chandra X-ray Detection
  52. GRB 250312A: Swift-XRT refined Analysis
  53. GRB 250312A: Enhanced Swift-XRT position
  54. GRB 250312B: Fermi GBM Final Localization
  55. GRB 250312A: Swift detection of a burst
  56. GRB 241213A: VIRT Optical Upper Limit
  57. GRB 241228A: VIRT Optical Upper Limit
  58. GRB 250311A/EP250311a: Optical upper limits with Kinder observations
  59. GRB 250311A: Swift-XRT observations
  60. GRB 250309B: 1.3m DFOT Optical observations
  61. GRB 250309B: PRIME near-infrared detection
  62. EP250304a: Chandra detection
  63. GRB 250311A: Tiled Swift observations
  64. EP250311a/GRB 250311A: EP-WXT detection
  65. GRB 250308A: CALET Gamma-Ray Burst Monitor detection
  66. GRB 250311B: SVOM detection of a burst
  67. GRB 250311A/MAXI J1457-026: MAXI/GSC detection
  68. IceCube-250309A: Upper limits from Fermi-GBM Observations
  69. Konus-Wind detection of GRB 250309B
  70. IPN triangulation of GRB 250308A (short)
  71. IPN triangulation of GRB 250309B
  72. IceCube-241224A: MASTER detection of PKS 1217+02 blazar flare with Zhirkov effect
  73. GRB 250309B/AT2025dws : COLIBRÍ Detection of the Optical Counterpart
  74. GRB 250309B: Swift-XRT refined Analysis
  75. GRB 250309B / AT2025dws: OSIRIS+/GTC spectroscopy z=1.898
  76. Liverpool Telecope observations of AT 2025dws / GRB 250309B
  77. GRB 250309B / AT2025dws: SAO RAS optical observations
  78. GRB 250309B / AT2025dws: Swift-UVOT detection
  79. AT 2025dws, likely optical counterpart of GRB 250309B: LCO confirmation of fast fading
  80. GRB250309B: One candidate counterpart from the Zwicky Transient Facility
  81. IceCube-250309A: No candidates from the Zwicky Transient Facility
  82. Fermi-LAT gamma-ray observations of IceCube-250309A
  83. GRB 250308A: SVOM/GRM detection of QPO in the tail emission
  84. GRB 250309B: Fermi GBM Final Localization
  85. Correction to GCN 39633 - Swift is observing GRB 250309B/IceCube-250309A!
  86. GRB 230509B: Tiled Swift observations
  87. IceCube-250309A - IceCube observation of a high-energy neutrino candidate track-like event
  88. EP250308a: GSP optical upper limit
  89. EP250308a: Einstein Probe detection of an X-ray transient
  90. GRB 250309A: Fermi GBM Final Real-time Localization
  91. GRB 250306A: EIRSAT-1 GMOD detection
  92. Konus-Wind detection of GRB 250306A
  93. GRB 250307A: Fermi GBM Final Real-time Localization
  94. GRB 250306A: NuSTAR detection of the prompt emission
  95. EP250304a: MeerKAT detection of a possible radio counterpart
  96. GRB 250305A: AstroSat CZTI detection
  97. GRB 250306A: AstroSat CZTI detection
  98. GRB 250306A: Swift detection of a burst
  99. LIGO/Virgo/KAGRA S250306ej: Retraction of GW compact binary merger candidate
  100. GRB 250305A: Fermi GBM Final Real-time Localization

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