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

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