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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').
  1. EP250304a: SVOM/VT optical observation
  2. EP250311a/GRB 250311A: EP-FXT follow-up observation
  3. ATCA detection of the radio counterpart of GRB 250309B-AT2025dws
  4. EP250302a: Chandra X-ray Detection
  5. GRB 250312A: Swift-XRT refined Analysis
  6. Fermi Gamma-ray Burst Monitor trigger 763509110/250312911 is not a GRB
  7. Fermi trigger No 763509110: Global MASTER-Net observations report
  8. Fermi GRB 250312B: Global MASTER-Net observations report
  9. GRB 250312A: Enhanced Swift-XRT position
  10. GRB 250312B: Fermi GBM Final Localization
  11. LIGO/Virgo/KAGRA S250304cb: Upper limits from Swift/BAT-GUANO
  12. GRB 250226B: Fermi GBM Observation
  13. Swift GRB 250312A: Global MASTER-Net observations report
  14. GRB 250302A: Fermi GBM Observation
  15. GRB 250309B/AT2025dws: Daochen/RC-10 optical counterpart observation
  16. GRB 250312A: Swift detection of a burst
  17. GRB 241213A: VIRT Optical Upper Limit
  18. GRB 241228A: VIRT Optical Upper Limit
  19. GRB 250311A/EP250311a: Optical upper limits with Kinder observations
  20. GRB 250223B: Fermi GBM Observation
  21. GRB 250311A: Swift-XRT observations
  22. GRB 250228A: Fermi GBM Observation
  23. GRB 230509B: 1.3m DFOT Optical observations
  24. IceCube-250309A: Upper limits from a search for additional neutrino events in IceCube
  25. EP250311a: Global MASTER-Net observations report
  26. GRB 250308A: Swift/BAT-GUANO localization skymap of a short burst
  27. GRB 250302A: Swift/BAT-GUANO localization skymap of a burst
  28. GRB 250228A: Swift/BAT-GUANO localization skymap of a likely short burst
  29. GRB 250226B: Swift/BAT-GUANO localization skymap of a likely long GRB
  30. GRB 250226A: Swift/BAT-GUANO localization skymap of a long GRB
  31. GRB 250223B: Swift/BAT-GUANO localization skymap of a short burst
  32. GRB 250309B: PRIME near-infrared detection
  33. EP250304a: Chandra detection
  34. GRB 250225B: Swift-BAT refined analysis
  35. GRB 250311A/EP250311a: TRT optical upper limit
  36. IceCube-250309A: MITSuME Akeno and Seimei/TriCCS optical observations
  37. GRB 250311A: Tiled Swift observations
  38. EP250311a/GRB 250311A: EP-WXT detection
  39. GRB 250308A: CALET Gamma-Ray Burst Monitor detection
  40. GRB 250311B: SVOM detection of a burst
  41. GRB 250309B: SVOM/VT optical observation
  42. GRB 250311A/MAXI J1457-026: MAXI/GSC detection
  43. The EP-WXT trigger 01709132425 is not a real source
  44. GRB 250309B / AT2025dws: further SAO RAS optical observations
  45. IceCube-250309A: Upper limits from Fermi-GBM Observations
  46. EP250308a: 1.6m Mephisto optical upper limits
  47. Konus-Wind detection of GRB 250309B
  48. GRB 250309B / AT2025dws: KMTNet-CTIO optical observations
  49. IPN triangulation of GRB 250308A (short)
  50. IPN triangulation of GRB 250309B
  51. IceCube-241224A: MASTER detection of PKS 1217+02 blazar flare with Zhirkov effect
  52. GRB 250309B/AT2025dws : COLIBRÍ Detection of the Optical Counterpart
  53. GRB 250309B: Swift-XRT refined Analysis
  54. GRB 250309B / IceCube-250309A: GECAM-B observations
  55. GRB 250309B / AT2025dws: OSIRIS+/GTC spectroscopy z=1.898
  56. Liverpool Telecope observations of AT 2025dws / GRB 250309B
  57. GRB 250309B / AT2025dws: SAO RAS optical observations
  58. GRB 250309B / AT2025dws: Swift-UVOT detection
  59. AT 2025dws, likely optical counterpart of GRB 250309B: LCO confirmation of fast fading
  60. GRB 250309B: Fermi GBM Observation
  61. Fermi GRB 250309B: Global MASTER-Net observations report
  62. Fermi GRB 250309A: Global MASTER-Net observations report
  63. GRB250309B: One candidate counterpart from the Zwicky Transient Facility
  64. IceCube-250309A: No candidates from the Zwicky Transient Facility
  65. Fermi-LAT gamma-ray observations of IceCube-250309A
  66. GRB 250308A: SVOM/GRM detection of QPO in the tail emission
  67. GRB 250309B: Fermi GBM Final Localization
  68. Correction to GCN 39633 - Swift is observing GRB 250309B/IceCube-250309A!
  69. GRB 230509B: Tiled Swift observations
  70. GRB 250308A: SVOM/GRM observation of a bright short burst
  71. IceCube-250309A - IceCube observation of a high-energy neutrino candidate track-like event
  72. IceCube Alert 250309.32: Global MASTER-Net observations report
  73. GRB 250309B: BALROG localization (Fermi Trigger 763198715 / GRB 250309318)
  74. EP250308a: Global MASTER-Net observations report
  75. EP250308a: GSP optical upper limit
  76. EP250308a: FTW optical and NIR upper limits
  77. EP250308a: Einstein Probe detection of an X-ray transient
  78. EP250308a: NOT optical upper limit
  79. GRB 250309A: Fermi GBM Final Real-time Localization
  80. GRB 250306A: EIRSAT-1 GMOD detection
  81. The EP-WXT trigger 01709132387 is likely a flaring star
  82. Fermi GRB 250307A: Global MASTER-Net observations report
  83. Konus-Wind detection of GRB 250306A
  84. GRB 250307A: Fermi GBM Final Real-time Localization
  85. GRB 250306A: Swift-BAT refined analysis
  86. GRB 250306A: NuSTAR detection of the prompt emission
  87. EP250304a: MeerKAT detection of a possible radio counterpart
  88. IceCube-241016A: MASTER flaring blazar 5BZU J073038.29-320820.2 with Zhirkov effect
  89. GRB 250305A: AstroSat CZTI detection
  90. EP250302a:Xinglong optical observations
  91. GRB 250306A: AstroSat CZTI detection
  92. Fermi trigger No 762963055: Global MASTER-Net observations report
  93. Fermi Gamma-ray Burst Monitor trigger 762963055/250306591 is not a GRB
  94. Swift GRB 250306A: Global MASTER-Net observations report
  95. LIGO/Virgo/KAGRA S250207bg: Update-5 NED Galaxies in the Localization Volume
  96. GRB 250306A: Swift detection of a burst
  97. LIGO/Virgo/KAGRA S250207bg: Updated Sky localization
  98. GRB250101A: Radio upper limits from VLA observations
  99. LIGO/Virgo/KAGRA S250306ej: Retraction of GW compact binary merger candidate
  100. GRB 250305A: SVOM/GRM observation of a burst

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