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

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