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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 250905A: Enhanced Swift-XRT position
  2. GRB 250904A: Swift/UVOT Detection
  3. GRB 250903A: Swift/UVOT detection
  4. GRB 250904A: Swift-XRT refined Analysis
  5. LIGO/Virgo/KAGRA S250904cv: Updated Sky localization
  6. LIGO/Virgo/KAGRA S250904br: Updated Sky localization
  7. EP detected a brightening of LMXB 1ES 1735-26.9
  8. GRB 250905A: KAIT optical upper limit
  9. GRB 250905A: Swift detection of a burst
  10. Swift GRB250905.09: Global MASTER-Net observations report
  11. Swift GRB 250904A: Global MASTER-Net observations report
  12. GRB 250904A: Enhanced Swift-XRT position
  13. IceCube-Cascade 250903A: Upper limits from a search for additional neutrino events in IceCube
  14. GRB 250904A: TRT optical counterpart detection
  15. EP250827a and EP250827b: Upper limit from Fermi-GBM Observations
  16. GRB 250902B: CALET Gamma-Ray Burst Monitor detection
  17. GRB 250904A: Prompt enhanced Swift-XRT position
  18. EP250827b: Gemini Spectroscopic Confirmation of AT2025wkm as a Ic-BL Supernova
  19. GRB 250904A: Swift detection of a burst
  20. GRB 250902A: CALET Gamma-Ray Burst Monitor detection
  21. LIGO/Virgo/KAGRA S250904ae: Updated Sky localization
  22. GRB 250902A: VZLUSAT-2 detection
  23. LIGO/Virgo/KAGRA S250904cv: Identification of a GW compact binary merger candidate
  24. GRB 250903A: Swift-XRT observations
  25. EP250903a: Swift-XRT observations
  26. EP#01709201209: Swift-XRT observations
  27. EP250903a: retraction of the LCO candidate, and discovery of the likely counterpart
  28. EP-WXT trigger 01709201209: Liverpool Telescope upper limits
  29. GRB 250830C: VZLUSAT-2 detection
  30. EP250903a: refined analysis of the EP-WXT and EP-FXT observations
  31. LIGO/Virgo/KAGRA S250904br: Identification of a GW compact binary merger candidate
  32. GRB 250903A: VLT X-shooter spectroscopic redshift z = 1.590
  33. The EP-WXT trigger 01709201209 is likely a flaring star
  34. LIGO/Virgo/KAGRA S250904ae: Identification of a GW compact binary merger candidate
  35. GRB 250903A: EP-FXT counterpart detection
  36. GRB 250902A: GECAM-B detection
  37. GRB 250903A: LCO optical observation
  38. GRB 250903A: LCO optical afterglow detection
  39. GRB 250903A: SVOM/VT optical confirmation with VHF data
  40. EP250903a: SVOM/VT optical confirmation
  41. EP250901a: Mondy, Assy and SAO RAS optical limits
  42. Subject GRB 250903A: SVOM/MXT afterglow detection
  43. EP250903a: LCO candidate counterpart discovery
  44. GRB 250903A: TRT optical counterpart detection
  45. GRB 250902B: AstroSat CZTI detection
  46. GRB 250903A: SVOM detection of a burst
  47. EP250903a: Global MASTER-Net observations report
  48. EP250903a: TRT optical observations
  49. EP250903a: Einstein Probe detection of an X-ray transient
  50. EP 250827B: Detection of supernova counterpart by LCO.
  51. EP/WXT01709201159: GOTO optical follow-up
  52. EP250827b / AT 2025wkm: TRT optical observations
  53. EP250827b: NOT spectroscopic observations and AT 2025wkm classification as a broad-lined type-Ic supernova
  54. EP250827b: continued Liverpool Telescope observations
  55. GRB 250902B: SVOM/GRM observation
  56. EP250827b: SVOM/VT observation of AT 2025wkm
  57. LIGO/VIRGO/KAGRA S250818k: No evidence for radio variability of AT2025ulz in MeerKAT 3 GHz data
  58. GRB 250831A (SVOM trigger sb25083102): KAIT confirmation of stellar flare
  59. Fermi GRB 250902B: Global MASTER-Net observations report
  60. Fermi-LAT Gamma-ray Observations of IceCube-250831A
  61. GRB 250902A: Fermi GBM Detection
  62. GRB 250901A: Swift/UVOT Upper Limit
  63. GRB 250902B: Fermi GBM Final Real-time Localization
  64. IceCube-250831A: Upper limits from a search for additional neutrino events in IceCube
  65. GRB 250830B: Swift-XRT afterglow detection
  66. LIGO/Virgo/KAGRA S250902av: 1 counterpart neutrino candidate event from an IceCube neutrino search
  67. LIGO/Virgo/KAGRA S250901cb: Updated Sky localization
  68. EP250827b: Liverpool Telescope observations
  69. GRB 250831A (SVOM trigger sb25083102): confirmation of a stellar flare by SVOM/VT
  70. GRB 250902A: SVOM/GRM observation
  71. EP250828a: Early near-infrared follow-up with MIRAGE on the MDM 1.3m telescope
  72. EP250901a: refined analysis of the EP-WXT and EP-FXT observations
  73. GRB 250901A: EP-FXT follow-up observation
  74. GRB 250901A: NOT optical observations
  75. GRB 250902A: Fermi GBM Final Real-time Localization
  76. IceCube-Cascade 250828A: Upper limits from a search for additional neutrino events in IceCube
  77. GRB 250901A: SVOM/VT optical afterglow with VHF data
  78. GRB 250901A: Swift-XRT afterglow detection
  79. EP250901a: Swift-XRT observations
  80. LIGO/Virgo/KAGRA S250830bp: DECam GW-MMADS candidates
  81. GRB 250901A: LCO optical upper limit
  82. EP250827b: Swift observations of AT 2025wkm
  83. LIGO/Virgo/KAGRA S250830bp: DECam DESGW Epoch 1 Candidates
  84. EP250827b: Gemini Spectroscopy of AT 2025wkm
  85. LIGO/Virgo/KAGRA S250901cb: Identification of a GW compact binary merger candidate
  86. EP250831a: NOT optical observations and tentative afterglow candidate
  87. EP250827b: FTW Observations of AT 2025wkm
  88. EP250827b: Contemporaneous detection of EP X-ray flare EP250827b and ZTF transient ZTF25abmpngy/AT2025wkm
  89. GRB 250901A: SVOM detection of a burst
  90. GRB 250831B: SVOM/GRM observation
  91. GRB 250830C: Insight-HXMT detection
  92. EP250901a: Mephisto optical upper limits
  93. GRB 250830C: GECAM-B detection
  94. EP250901a: Global MASTER-Net observations report
  95. GRB 250830C: AstroSat CZTI detection of a long burst
  96. EP250901a: Einstein Probe detection of an X-ray transient
  97. LIGO/Virgo/KAGRA S250830m: Updated Sky localization
  98. EP250831a: EP-FXT follow-up observation
  99. EP250831a: Swift-XRT observations
  100. LIGO/Virgo/KAGRA S250831cc: Coverage and upper limits from MAXI/GSC observations

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