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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 250911A: Swift-XRT observations
  2. GRB 250911A: COLIBRÍ optical counterpart candidate
  3. GRB 250911A: Swift detection of a burst
  4. LIGO/Virgo/KAGRA S250906ca: Updated Sky localization
  5. GRB 250910B: BALROG localization (Fermi Trigger 779223130 / GRB 250910786)
  6. GRB 250910B: Fermi GBM Final Real-time Localization
  7. GRB 250910A / EP250910a: VLT/HAWK-I near-infrared observations
  8. EP250910a/GRB 250910A: EP-WXT detection of a fast X-ray transient
  9. GRB 250909B: AstroSat CZTI detection of a long burst
  10. GRB 250910A: SVOM/VT optical upper limit
  11. EP250908C: GROND observation of the fading optical counterpart
  12. GRB 250910A: LCO optical upper limit
  13. GRB 250909A: AstroSat CZTI detection
  14. GRB 250910A: SVOM/MXT possible afterglow detection
  15. GRB 250910A: SVOM detection of a faint burst
  16. LIGO/Virgo/KAGRA S250910b: Retraction of GW compact binary merger candidate
  17. GRB 250702B: Late time Chandra observations
  18. EP250908b/EP#01709240653: Swift/UVOT Detection
  19. EP#01709240653: Swift-XRT observations
  20. The EP-WXT trigger 01709240674 is triggered by the known source SS Cyg
  21. EP250908c: refined analysis of the EP-WXT and EP-FXT observations
  22. GRB 250907A: CALET Gamma-Ray Burst Monitor detection
  23. EP250908c: SVOM/VT optical observation
  24. EP250908c: VLT/FORS2 optical counterpart identification
  25. EP250908b: SVOM/VT optical candidate (Coordinate supplement for GCN 41758)
  26. EP250908b: SVOM/VT optical candidate
  27. The EP-WXT trigger EP250908a/01709240652 is not a real source
  28. EP250908c: Global MASTER-Net observations report
  29. Fermi GRB 250909A: Global MASTER-Net observations report
  30. EP250908c: Einstein Probe detection of an X-ray transient
  31. GRB 250909A: Fermi GBM Final Real-time Localization
  32. EP250908b: EP-WXT detection of a fast X-ray transient and EP-FXT observation
  33. EP#01709240652 (possibly EP250908a): FTW optical and NIR observations
  34. LIGO/Virgo/KAGRA S250908y: Identification of a GW compact binary merger candidate
  35. GRB 250907A: GECAM-B detection
  36. GRB 250905A: Swift-BAT refined analysis
  37. Fermi-LAT Gamma-ray Observations of IceCube-250905A
  38. GRB 250903A: Swift-XRT afterglow detection
  39. LIGO/Virgo/KAGRA S250906ca: Identification of a GW compact binary merger candidate
  40. IceCube-250905A: Upper limits from a search for additional neutrino events in IceCube
  41. SVOM/sb25090605: detection of an X-ray transient from the LMXB 4U 0513-40
  42. EP250905a: Liverpool Telescope i-band upper limits
  43. LIGO/Virgo/KAGRA S250830bp: DECam/SOAR GW-MMADS updates
  44. EP250905b: EP-FXT follow-up observation
  45. LIGO/Virgo/KAGRA S250830bp: DECam DESGW Epoch 2 Candidates
  46. EP250905a: Liverpool Telescope observations
  47. EP250905a: refined analysis of the EP-WXT and EP-FXT observations
  48. EP250905b: Global MASTER-Net observations report
  49. EP250905b: EP-WXT detection of a fast X-ray transient
  50. EP250905a: FTW one optical and multiple NIR counterpart candidates
  51. GRB 250905A: Swift-XRT refined Analysis
  52. EP250905a: JinShan likely optical counterpart detection
  53. IceCube-250905A - IceCube observation of a high-energy neutrino candidate track-like event
  54. GRB 250904A: Swift-BAT refined analysis
  55. IceCube Alert 250905.84: Global MASTER-Net observations report
  56. GRB 250905A: Swift/UVOT Upper Limits
  57. EP250905a: Global MASTER-Net observations report
  58. GRB 250901A - SVOM/ECLAIRs refined analysis
  59. EP250905a: Einstein Probe detection of an X-ray transient
  60. GRB 250905B: Fermi GBM Final Localization
  61. GRB250904A: Liverpool Telescope upper limits
  62. GRB 250905A: Enhanced Swift-XRT position
  63. GRB 250904A: Swift/UVOT Detection
  64. GRB 250903A: Swift/UVOT detection
  65. GRB 250904A: Swift-XRT refined Analysis
  66. LIGO/Virgo/KAGRA S250904cv: Updated Sky localization
  67. LIGO/Virgo/KAGRA S250904br: Updated Sky localization
  68. EP detected a brightening of LMXB 1ES 1735-26.9
  69. GRB 250905A: KAIT optical upper limit
  70. GRB 250905A: Swift detection of a burst
  71. Swift GRB250905.09: Global MASTER-Net observations report
  72. Swift GRB 250904A: Global MASTER-Net observations report
  73. GRB 250904A: Enhanced Swift-XRT position
  74. IceCube-Cascade 250903A: Upper limits from a search for additional neutrino events in IceCube
  75. GRB 250904A: TRT optical counterpart detection
  76. EP250827a and EP250827b: Upper limit from Fermi-GBM Observations
  77. GRB 250902B: CALET Gamma-Ray Burst Monitor detection
  78. GRB 250904A: Prompt enhanced Swift-XRT position
  79. EP250827b: Gemini Spectroscopic Confirmation of AT2025wkm as a Ic-BL Supernova
  80. GRB 250904A: Swift detection of a burst
  81. GRB 250902A: CALET Gamma-Ray Burst Monitor detection
  82. LIGO/Virgo/KAGRA S250904ae: Updated Sky localization
  83. GRB 250902A: VZLUSAT-2 detection
  84. LIGO/Virgo/KAGRA S250904cv: Identification of a GW compact binary merger candidate
  85. GRB 250903A: Swift-XRT observations
  86. EP250903a: Swift-XRT observations
  87. EP#01709201209: Swift-XRT observations
  88. EP250903a: retraction of the LCO candidate, and discovery of the likely counterpart
  89. EP-WXT trigger 01709201209: Liverpool Telescope upper limits
  90. GRB 250830C: VZLUSAT-2 detection
  91. EP250903a: refined analysis of the EP-WXT and EP-FXT observations
  92. LIGO/Virgo/KAGRA S250904br: Identification of a GW compact binary merger candidate
  93. GRB 250903A: VLT X-shooter spectroscopic redshift z = 1.590
  94. The EP-WXT trigger 01709201209 is likely a flaring star
  95. LIGO/Virgo/KAGRA S250904ae: Identification of a GW compact binary merger candidate
  96. GRB 250903A: EP-FXT counterpart detection
  97. GRB 250902A: GECAM-B detection
  98. GRB 250903A: LCO optical observation
  99. GRB 250903A: LCO optical afterglow detection
  100. GRB 250903A: SVOM/VT optical confirmation with VHF data

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