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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"

32500 results found.

  1. EP250911a: SAO RAS optical observations
  2. EP250911a: Swift-XRT observations
  3. EP250911a: Optical detection with Kinder observations
  4. GRB 250911A: Swift/UVOT Detection
  5. GRB 250910A / EP250910a: Swift-XRT afterglow detection
  6. GRB 250910A / EP250910a: SVOM/VT afterglow confirmation
  7. GRB 250909B: Insight-HXMT detection
  8. GRB 250909B: SVOM/GRM observation
  9. LIGO/Virgo/KAGRA S250911ac: Updated Sky localization and Source Classification
  10. GRB 250910A / EP250910a : VLT/HAWK-I NIR counterpart discovery
  11. EP250911a: COLIBRÍ optical observations
  12. LIGO/Virgo/KAGRA S250908y: Updated Sky localization
  13. Fermi GRB 250910B: Global MASTER-Net observations report
  14. EP250911a: LCO optical counterpart discovery
  15. EP250910a: Global MASTER-Net observations report
  16. GRB 250404A / EP250404a: spectroscopic redshift at z = 1.88 (correction to GCN 40084)
  17. LIGO/Virgo/KAGRA S250911ac: Identification of a GW compact binary merger candidate
  18. GRB 250903A: SVOM/ECLAIRs refined analysis
  19. GRB 250911A: COLIBRÍ optical counterpart candidate
  20. LIGO/Virgo/KAGRA S250906ca: Updated Sky localization
  21. GRB 250910A / EP250910a: VLT/HAWK-I near-infrared observations
  22. EP250910a/GRB 250910A: EP-WXT detection of a fast X-ray transient
  23. GRB 250910A: SVOM/VT optical upper limit
  24. EP250908C: GROND observation of the fading optical counterpart
  25. GRB 250910A: LCO optical upper limit
  26. GRB 250909A: AstroSat CZTI detection
  27. GRB 250910A: SVOM/MXT possible afterglow detection
  28. GRB 250702B: Late time Chandra observations
  29. EP250908b/EP#01709240653: Swift/UVOT Detection
  30. EP250908c: refined analysis of the EP-WXT and EP-FXT observations
  31. GRB 250907A: CALET Gamma-Ray Burst Monitor detection
  32. EP250908c: SVOM/VT optical observation
  33. EP250908c: VLT/FORS2 optical counterpart identification
  34. EP250908b: SVOM/VT optical candidate (Coordinate supplement for GCN 41758)
  35. EP250908b: SVOM/VT optical candidate
  36. EP250908c: Global MASTER-Net observations report
  37. Fermi GRB 250909A: Global MASTER-Net observations report
  38. LIGO/Virgo/KAGRA S250908y: Identification of a GW compact binary merger candidate
  39. GRB 250905A: Swift-BAT refined analysis
  40. Fermi-LAT Gamma-ray Observations of IceCube-250905A
  41. GRB 250903A: Swift-XRT afterglow detection
  42. LIGO/Virgo/KAGRA S250906ca: Identification of a GW compact binary merger candidate
  43. IceCube-250905A: Upper limits from a search for additional neutrino events in IceCube
  44. EP250905a: Liverpool Telescope i-band upper limits
  45. LIGO/Virgo/KAGRA S250830bp: DECam/SOAR GW-MMADS updates
  46. EP250905b: EP-FXT follow-up observation
  47. LIGO/Virgo/KAGRA S250830bp: DECam DESGW Epoch 2 Candidates
  48. EP250905a: Liverpool Telescope observations
  49. EP250905a: refined analysis of the EP-WXT and EP-FXT observations
  50. EP250905b: Global MASTER-Net observations report
  51. EP250905a: FTW one optical and multiple NIR counterpart candidates
  52. EP250905a: JinShan likely optical counterpart detection
  53. GRB 250904A: Swift-BAT refined analysis
  54. GRB 250905A: Swift/UVOT Upper Limits
  55. EP250905a: Global MASTER-Net observations report
  56. GRB 250901A - SVOM/ECLAIRs refined analysis
  57. GRB250904A: Liverpool Telescope upper limits
  58. GRB 250904A: Swift/UVOT Detection
  59. GRB 250903A: Swift/UVOT detection
  60. LIGO/Virgo/KAGRA S250904cv: Updated Sky localization
  61. LIGO/Virgo/KAGRA S250904br: Updated Sky localization
  62. GRB 250905A: KAIT optical upper limit
  63. Swift GRB 250904A: Global MASTER-Net observations report
  64. GRB 250904A: TRT optical counterpart detection
  65. EP250827a and EP250827b: Upper limit from Fermi-GBM Observations
  66. GRB 250902B: CALET Gamma-Ray Burst Monitor detection
  67. EP250827b: Gemini Spectroscopic Confirmation of AT2025wkm as a Ic-BL Supernova
  68. GRB 250902A: CALET Gamma-Ray Burst Monitor detection
  69. LIGO/Virgo/KAGRA S250904ae: Updated Sky localization
  70. GRB 250902A: VZLUSAT-2 detection
  71. LIGO/Virgo/KAGRA S250904cv: Identification of a GW compact binary merger candidate
  72. GRB 250903A: Swift-XRT observations
  73. EP250903a: Swift-XRT observations
  74. EP#01709201209: Swift-XRT observations
  75. EP250903a: retraction of the LCO candidate, and discovery of the likely counterpart
  76. EP-WXT trigger 01709201209: Liverpool Telescope upper limits
  77. GRB 250830C: VZLUSAT-2 detection
  78. EP250903a: refined analysis of the EP-WXT and EP-FXT observations
  79. LIGO/Virgo/KAGRA S250904br: Identification of a GW compact binary merger candidate
  80. GRB 250903A: VLT X-shooter spectroscopic redshift z = 1.590
  81. LIGO/Virgo/KAGRA S250904ae: Identification of a GW compact binary merger candidate
  82. GRB 250903A: EP-FXT counterpart detection
  83. GRB 250902A: GECAM-B detection
  84. GRB 250903A: LCO optical observation
  85. GRB 250903A: LCO optical afterglow detection
  86. GRB 250903A: SVOM/VT optical confirmation with VHF data
  87. EP250903a: SVOM/VT optical confirmation
  88. EP250901a: Mondy, Assy and SAO RAS optical limits
  89. Subject GRB 250903A: SVOM/MXT afterglow detection
  90. EP250903a: LCO candidate counterpart discovery
  91. GRB 250903A: TRT optical counterpart detection
  92. GRB 250902B: AstroSat CZTI detection
  93. EP250903a: Global MASTER-Net observations report
  94. EP250903a: TRT optical observations
  95. EP250903a: Einstein Probe detection of an X-ray transient
  96. EP 250827B: Detection of supernova counterpart by LCO.
  97. EP250827b / AT 2025wkm: TRT optical observations
  98. EP250827b: NOT spectroscopic observations and AT 2025wkm classification as a broad-lined type-Ic supernova
  99. EP250827b: continued Liverpool Telescope observations
  100. GRB 250902B: SVOM/GRM observation

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