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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 250311A: Swift-XRT observations
  2. GRB 250228A: Fermi GBM Observation
  3. GRB 250309B: 1.3m DFOT Optical observations
  4. IceCube-250309A: Upper limits from a search for additional neutrino events in IceCube
  5. EP250311a: Global MASTER-Net observations report
  6. GRB 250308A: Swift/BAT-GUANO localization skymap of a short burst
  7. GRB 250302A: Swift/BAT-GUANO localization skymap of a burst
  8. GRB 250228A: Swift/BAT-GUANO localization skymap of a likely short burst
  9. GRB 250226B: Swift/BAT-GUANO localization skymap of a likely long GRB
  10. GRB 250226A: Swift/BAT-GUANO localization skymap of a long GRB
  11. GRB 250223B: Swift/BAT-GUANO localization skymap of a short burst
  12. GRB 250309B: PRIME near-infrared detection
  13. EP250304a: Chandra detection
  14. GRB 250225B: Swift-BAT refined analysis
  15. GRB 250311A/EP250311a: TRT optical upper limit
  16. IceCube-250309A: MITSuME Akeno and Seimei/TriCCS optical observations
  17. GRB 250311A: Tiled Swift observations
  18. EP250311a/GRB 250311A: EP-WXT detection
  19. GRB 250308A: CALET Gamma-Ray Burst Monitor detection
  20. GRB 250311B: SVOM detection of a burst
  21. GRB 250309B: SVOM/VT optical observation
  22. GRB 250311A/MAXI J1457-026: MAXI/GSC detection
  23. The EP-WXT trigger 01709132425 is not a real source
  24. GRB 250309B / AT2025dws: further SAO RAS optical observations
  25. IceCube-250309A: Upper limits from Fermi-GBM Observations
  26. EP250308a: 1.6m Mephisto optical upper limits
  27. Konus-Wind detection of GRB 250309B
  28. GRB 250309B / AT2025dws: KMTNet-CTIO optical observations
  29. IPN triangulation of GRB 250308A (short)
  30. IPN triangulation of GRB 250309B
  31. IceCube-241224A: MASTER detection of PKS 1217+02 blazar flare with Zhirkov effect
  32. GRB 250309B/AT2025dws : COLIBRÍ Detection of the Optical Counterpart
  33. GRB 250309B: Swift-XRT refined Analysis
  34. GRB 250309B / IceCube-250309A: GECAM-B observations
  35. GRB 250309B / AT2025dws: OSIRIS+/GTC spectroscopy z=1.898
  36. Liverpool Telecope observations of AT 2025dws / GRB 250309B
  37. GRB 250309B / AT2025dws: SAO RAS optical observations
  38. GRB 250309B / AT2025dws: Swift-UVOT detection
  39. AT 2025dws, likely optical counterpart of GRB 250309B: LCO confirmation of fast fading
  40. GRB 250309B: Fermi GBM Observation
  41. Fermi GRB 250309B: Global MASTER-Net observations report
  42. Fermi GRB 250309A: Global MASTER-Net observations report
  43. GRB250309B: One candidate counterpart from the Zwicky Transient Facility
  44. IceCube-250309A: No candidates from the Zwicky Transient Facility
  45. Fermi-LAT gamma-ray observations of IceCube-250309A
  46. GRB 250308A: SVOM/GRM detection of QPO in the tail emission
  47. GRB 250309B: Fermi GBM Final Localization
  48. Correction to GCN 39633 - Swift is observing GRB 250309B/IceCube-250309A!
  49. GRB 230509B: Tiled Swift observations
  50. GRB 250308A: SVOM/GRM observation of a bright short burst
  51. IceCube-250309A - IceCube observation of a high-energy neutrino candidate track-like event
  52. IceCube Alert 250309.32: Global MASTER-Net observations report
  53. GRB 250309B: BALROG localization (Fermi Trigger 763198715 / GRB 250309318)
  54. EP250308a: Global MASTER-Net observations report
  55. EP250308a: GSP optical upper limit
  56. EP250308a: FTW optical and NIR upper limits
  57. EP250308a: Einstein Probe detection of an X-ray transient
  58. EP250308a: NOT optical upper limit
  59. GRB 250309A: Fermi GBM Final Real-time Localization
  60. GRB 250306A: EIRSAT-1 GMOD detection
  61. The EP-WXT trigger 01709132387 is likely a flaring star
  62. Fermi GRB 250307A: Global MASTER-Net observations report
  63. Konus-Wind detection of GRB 250306A
  64. GRB 250307A: Fermi GBM Final Real-time Localization
  65. GRB 250306A: Swift-BAT refined analysis
  66. GRB 250306A: NuSTAR detection of the prompt emission
  67. EP250304a: MeerKAT detection of a possible radio counterpart
  68. IceCube-241016A: MASTER flaring blazar 5BZU J073038.29-320820.2 with Zhirkov effect
  69. GRB 250305A: AstroSat CZTI detection
  70. EP250302a:Xinglong optical observations
  71. GRB 250306A: AstroSat CZTI detection
  72. Fermi trigger No 762963055: Global MASTER-Net observations report
  73. Fermi Gamma-ray Burst Monitor trigger 762963055/250306591 is not a GRB
  74. Swift GRB 250306A: Global MASTER-Net observations report
  75. LIGO/Virgo/KAGRA S250207bg: Update-5 NED Galaxies in the Localization Volume
  76. GRB 250306A: Swift detection of a burst
  77. LIGO/Virgo/KAGRA S250207bg: Updated Sky localization
  78. GRB250101A: Radio upper limits from VLA observations
  79. LIGO/Virgo/KAGRA S250306ej: Retraction of GW compact binary merger candidate
  80. GRB 250305A: SVOM/GRM observation of a burst
  81. The EP-WXT trigger 01709132323 is likely a flaring star
  82. EP250304A: Upper limits from Fermi-GBM Observations
  83. Fermi GRB 250305A: Global MASTER-Net observations report
  84. Fermi-LAT Gamma-ray Observations of IceCube-250302A
  85. GRB 250305A: Fermi GBM Final Real-time Localization
  86. EP250302a: Optical Observations at CrAO and SAO RAS
  87. GRB 250219A: SVOM/C-GFT optical upper limit at early phase
  88. EP 250304A: Optical counterpart detection by LCO
  89. EP250302A: 1.3m DFOT optical afterglow detection
  90. IceCube-250302A: Upper limits from a search for additional neutrino events in IceCube
  91. EP250304a: refined analysis of the EP-WXT and EP-FXT observations
  92. Konus-Wind detection of GRB 250222A
  93. EP250304a: REM NIR upper limits
  94. IPN triangulation of GRB 250222A
  95. EP250304a: Swift/UVOT detection of an optical counterpart with a rising light curve
  96. EP250302a: Mondy Continued Optical Observations
  97. EP250304a: VLT/X-shooter redshift z = 0.200
  98. EP250304a: Swift-XRT detection of a fading X-ray source
  99. EP250304a: TRT optical counterpart detection
  100. LIGO/Virgo/KAGRA S250304cb: Identification of a GW compact binary merger candidate

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