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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. Liverpool Telecope observations of AT 2025dws / GRB 250309B
  2. GRB 250309B / AT2025dws: SAO RAS optical observations
  3. GRB 250309B / AT2025dws: Swift-UVOT detection
  4. AT 2025dws, likely optical counterpart of GRB 250309B: LCO confirmation of fast fading
  5. GRB 250309B: Fermi GBM Observation
  6. Fermi GRB 250309B: Global MASTER-Net observations report
  7. Fermi GRB 250309A: Global MASTER-Net observations report
  8. GRB250309B: One candidate counterpart from the Zwicky Transient Facility
  9. IceCube-250309A: No candidates from the Zwicky Transient Facility
  10. Fermi-LAT gamma-ray observations of IceCube-250309A
  11. GRB 250308A: SVOM/GRM detection of QPO in the tail emission
  12. GRB 250309B: Fermi GBM Final Localization
  13. Correction to GCN 39633 - Swift is observing GRB 250309B/IceCube-250309A!
  14. GRB 230509B: Tiled Swift observations
  15. GRB 250308A: SVOM/GRM observation of a bright short burst
  16. IceCube-250309A - IceCube observation of a high-energy neutrino candidate track-like event
  17. IceCube Alert 250309.32: Global MASTER-Net observations report
  18. GRB 250309B: BALROG localization (Fermi Trigger 763198715 / GRB 250309318)
  19. EP250308a: Global MASTER-Net observations report
  20. EP250308a: GSP optical upper limit
  21. EP250308a: FTW optical and NIR upper limits
  22. EP250308a: Einstein Probe detection of an X-ray transient
  23. EP250308a: NOT optical upper limit
  24. GRB 250309A: Fermi GBM Final Real-time Localization
  25. GRB 250306A: EIRSAT-1 GMOD detection
  26. The EP-WXT trigger 01709132387 is likely a flaring star
  27. Fermi GRB 250307A: Global MASTER-Net observations report
  28. Konus-Wind detection of GRB 250306A
  29. GRB 250307A: Fermi GBM Final Real-time Localization
  30. GRB 250306A: Swift-BAT refined analysis
  31. GRB 250306A: NuSTAR detection of the prompt emission
  32. EP250304a: MeerKAT detection of a possible radio counterpart
  33. IceCube-241016A: MASTER flaring blazar 5BZU J073038.29-320820.2 with Zhirkov effect
  34. GRB 250305A: AstroSat CZTI detection
  35. EP250302a:Xinglong optical observations
  36. GRB 250306A: AstroSat CZTI detection
  37. Fermi trigger No 762963055: Global MASTER-Net observations report
  38. Fermi Gamma-ray Burst Monitor trigger 762963055/250306591 is not a GRB
  39. Swift GRB 250306A: Global MASTER-Net observations report
  40. LIGO/Virgo/KAGRA S250207bg: Update-5 NED Galaxies in the Localization Volume
  41. GRB 250306A: Swift detection of a burst
  42. LIGO/Virgo/KAGRA S250207bg: Updated Sky localization
  43. GRB250101A: Radio upper limits from VLA observations
  44. LIGO/Virgo/KAGRA S250306ej: Retraction of GW compact binary merger candidate
  45. GRB 250305A: SVOM/GRM observation of a burst
  46. The EP-WXT trigger 01709132323 is likely a flaring star
  47. EP250304A: Upper limits from Fermi-GBM Observations
  48. Fermi GRB 250305A: Global MASTER-Net observations report
  49. Fermi-LAT Gamma-ray Observations of IceCube-250302A
  50. GRB 250305A: Fermi GBM Final Real-time Localization
  51. EP250302a: Optical Observations at CrAO and SAO RAS
  52. GRB 250219A: SVOM/C-GFT optical upper limit at early phase
  53. EP 250304A: Optical counterpart detection by LCO
  54. EP250302A: 1.3m DFOT optical afterglow detection
  55. IceCube-250302A: Upper limits from a search for additional neutrino events in IceCube
  56. EP250304a: refined analysis of the EP-WXT and EP-FXT observations
  57. Konus-Wind detection of GRB 250222A
  58. EP250304a: REM NIR upper limits
  59. IPN triangulation of GRB 250222A
  60. EP250304a: Swift/UVOT detection of an optical counterpart with a rising light curve
  61. EP250302a: Mondy Continued Optical Observations
  62. EP250304a: VLT/X-shooter redshift z = 0.200
  63. EP250304a: Swift-XRT detection of a fading X-ray source
  64. EP250304a: TRT optical counterpart detection
  65. LIGO/Virgo/KAGRA S250304cb: Identification of a GW compact binary merger candidate
  66. EP250304a: Global MASTER-Net observations report
  67. EP250304a: Einstein Probe detection of an X-ray transient
  68. The EP-WXT trigger 01709132212 is not a real source
  69. EP250302a: SVOM/VT optical observation
  70. LIGO/Virgo/KAGRA S250223dk and Swift/BAT-GUANO ID 762004910: Swift/UVOT Upper Limits
  71. EP250302a: SAO RAS optical observations
  72. EP250302a : GIT optical follow-up
  73. EP250302a: VLT/X-shooter redshift confirmation
  74. EP250225a: the candidate optical counterpart is an AGN
  75. EP250302a: Kinder optical follow-up observations
  76. LIGO/Virgo/KAGRA S250302av: 2 counterpart neutrino candidate events from an IceCube neutrino search
  77. EP250302a: Swift/UVOT detection
  78. EP250302a: NUTTelA-TAO Early Measurments
  79. EP250302a: optical observation from the INAF Asiago Observatory
  80. EP250302a: REM NIR upper limits
  81. IceCube-241113A: MASTER flaring blazar 5BZB J1311+0853 with Zhirkov effect
  82. EP250302a: Mondy Observations and Optical Light Curve
  83. EP250302a: VLT/MUSE optical redshift z = 1.131
  84. INTEGRAL: end of scientific operations
  85. EP250302A: VLT near-infrared observations
  86. EP250302A: VLT/X-shooter tentative redshift
  87. EP250302a: OHP/T193 optical and spectroscopic observations
  88. EP250302a: Global MASTER-Net observations report
  89. EP250302a: Xinglong F60B optical observation
  90. EP250302a: Swift-XRT observations of a fading X-ray source
  91. EP250302a: Einstein Probe detection of an X-ray transient
  92. EP250302a: SVOM/C-GFT optical observations
  93. GRB 250226A: GRANDMA Optical Observations
  94. EP250302a: Montarrenti Observatory optical detection
  95. Fermi GRB 250302A: Global MASTER-Net observations report
  96. EP250302a: FTW optical and NIR detection
  97. EP250302a: Nanshan/HMT optical counterpart detection
  98. IceCube-250302A - IceCube observation of a high-energy neutrino candidate track-like event
  99. GRB 250302A: Fermi GBM Final Real-time Localization
  100. GRB 250228A: Fermi GBM Final Localization

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