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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. EP250910a: Global MASTER-Net observations report
  2. EP250911a: Einstein Probe detection of an X-ray transient
  3. GRB 250404A / EP250404a: spectroscopic redshift at z = 1.88 (correction to GCN 40084)
  4. LIGO/Virgo/KAGRA S250911ac: Identification of a GW compact binary merger candidate
  5. GRB 250903A: SVOM/ECLAIRs refined analysis
  6. GRB 250911A: Enhanced Swift-XRT position
  7. GRB 250911A: Swift-XRT observations
  8. GRB 250911A: COLIBRÍ optical counterpart candidate
  9. GRB 250911A: Swift detection of a burst
  10. LIGO/Virgo/KAGRA S250906ca: Updated Sky localization
  11. GRB 250910B: BALROG localization (Fermi Trigger 779223130 / GRB 250910786)
  12. GRB 250910B: Fermi GBM Final Real-time Localization
  13. GRB 250910A / EP250910a: VLT/HAWK-I near-infrared observations
  14. EP250910a/GRB 250910A: EP-WXT detection of a fast X-ray transient
  15. GRB 250909B: AstroSat CZTI detection of a long burst
  16. GRB 250910A: SVOM/VT optical upper limit
  17. EP250908C: GROND observation of the fading optical counterpart
  18. GRB 250910A: LCO optical upper limit
  19. GRB 250909A: AstroSat CZTI detection
  20. GRB 250910A: SVOM/MXT possible afterglow detection
  21. GRB 250910A: SVOM detection of a faint burst
  22. LIGO/Virgo/KAGRA S250910b: Retraction of GW compact binary merger candidate
  23. GRB 250702B: Late time Chandra observations
  24. EP250908b/EP#01709240653: Swift/UVOT Detection
  25. EP#01709240653: Swift-XRT observations
  26. The EP-WXT trigger 01709240674 is triggered by the known source SS Cyg
  27. EP250908c: refined analysis of the EP-WXT and EP-FXT observations
  28. GRB 250907A: CALET Gamma-Ray Burst Monitor detection
  29. EP250908c: SVOM/VT optical observation
  30. EP250908c: VLT/FORS2 optical counterpart identification
  31. EP250908b: SVOM/VT optical candidate (Coordinate supplement for GCN 41758)
  32. EP250908b: SVOM/VT optical candidate
  33. The EP-WXT trigger EP250908a/01709240652 is not a real source
  34. EP250908c: Global MASTER-Net observations report
  35. Fermi GRB 250909A: Global MASTER-Net observations report
  36. EP250908c: Einstein Probe detection of an X-ray transient
  37. GRB 250909A: Fermi GBM Final Real-time Localization
  38. EP250908b: EP-WXT detection of a fast X-ray transient and EP-FXT observation
  39. EP#01709240652 (possibly EP250908a): FTW optical and NIR observations
  40. LIGO/Virgo/KAGRA S250908y: Identification of a GW compact binary merger candidate
  41. GRB 250907A: GECAM-B detection
  42. GRB 250905A: Swift-BAT refined analysis
  43. Fermi-LAT Gamma-ray Observations of IceCube-250905A
  44. GRB 250903A: Swift-XRT afterglow detection
  45. LIGO/Virgo/KAGRA S250906ca: Identification of a GW compact binary merger candidate
  46. IceCube-250905A: Upper limits from a search for additional neutrino events in IceCube
  47. SVOM/sb25090605: detection of an X-ray transient from the LMXB 4U 0513-40
  48. EP250905a: Liverpool Telescope i-band upper limits
  49. LIGO/Virgo/KAGRA S250830bp: DECam/SOAR GW-MMADS updates
  50. EP250905b: EP-FXT follow-up observation
  51. LIGO/Virgo/KAGRA S250830bp: DECam DESGW Epoch 2 Candidates
  52. EP250905a: Liverpool Telescope observations
  53. EP250905a: refined analysis of the EP-WXT and EP-FXT observations
  54. EP250905b: Global MASTER-Net observations report
  55. EP250905b: EP-WXT detection of a fast X-ray transient
  56. EP250905a: FTW one optical and multiple NIR counterpart candidates
  57. GRB 250905A: Swift-XRT refined Analysis
  58. EP250905a: JinShan likely optical counterpart detection
  59. IceCube-250905A - IceCube observation of a high-energy neutrino candidate track-like event
  60. GRB 250904A: Swift-BAT refined analysis
  61. IceCube Alert 250905.84: Global MASTER-Net observations report
  62. GRB 250905A: Swift/UVOT Upper Limits
  63. EP250905a: Global MASTER-Net observations report
  64. GRB 250901A - SVOM/ECLAIRs refined analysis
  65. EP250905a: Einstein Probe detection of an X-ray transient
  66. GRB 250905B: Fermi GBM Final Localization
  67. GRB250904A: Liverpool Telescope upper limits
  68. GRB 250905A: Enhanced Swift-XRT position
  69. GRB 250904A: Swift/UVOT Detection
  70. GRB 250903A: Swift/UVOT detection
  71. GRB 250904A: Swift-XRT refined Analysis
  72. LIGO/Virgo/KAGRA S250904cv: Updated Sky localization
  73. LIGO/Virgo/KAGRA S250904br: Updated Sky localization
  74. EP detected a brightening of LMXB 1ES 1735-26.9
  75. GRB 250905A: KAIT optical upper limit
  76. GRB 250905A: Swift detection of a burst
  77. Swift GRB250905.09: Global MASTER-Net observations report
  78. Swift GRB 250904A: Global MASTER-Net observations report
  79. GRB 250904A: Enhanced Swift-XRT position
  80. IceCube-Cascade 250903A: Upper limits from a search for additional neutrino events in IceCube
  81. GRB 250904A: TRT optical counterpart detection
  82. EP250827a and EP250827b: Upper limit from Fermi-GBM Observations
  83. GRB 250902B: CALET Gamma-Ray Burst Monitor detection
  84. GRB 250904A: Prompt enhanced Swift-XRT position
  85. EP250827b: Gemini Spectroscopic Confirmation of AT2025wkm as a Ic-BL Supernova
  86. GRB 250904A: Swift detection of a burst
  87. GRB 250902A: CALET Gamma-Ray Burst Monitor detection
  88. LIGO/Virgo/KAGRA S250904ae: Updated Sky localization
  89. GRB 250902A: VZLUSAT-2 detection
  90. LIGO/Virgo/KAGRA S250904cv: Identification of a GW compact binary merger candidate
  91. GRB 250903A: Swift-XRT observations
  92. EP250903a: Swift-XRT observations
  93. EP#01709201209: Swift-XRT observations
  94. EP250903a: retraction of the LCO candidate, and discovery of the likely counterpart
  95. EP-WXT trigger 01709201209: Liverpool Telescope upper limits
  96. GRB 250830C: VZLUSAT-2 detection
  97. EP250903a: refined analysis of the EP-WXT and EP-FXT observations
  98. LIGO/Virgo/KAGRA S250904br: Identification of a GW compact binary merger candidate
  99. GRB 250903A: VLT X-shooter spectroscopic redshift z = 1.590
  100. The EP-WXT trigger 01709201209 is likely a flaring star

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