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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. EP#01709201209: Swift-XRT observations
  2. EP250903a: retraction of the LCO candidate, and discovery of the likely counterpart
  3. EP-WXT trigger 01709201209: Liverpool Telescope upper limits
  4. GRB 250830C: VZLUSAT-2 detection
  5. EP250903a: refined analysis of the EP-WXT and EP-FXT observations
  6. LIGO/Virgo/KAGRA S250904br: Identification of a GW compact binary merger candidate
  7. GRB 250903A: VLT X-shooter spectroscopic redshift z = 1.590
  8. The EP-WXT trigger 01709201209 is likely a flaring star
  9. LIGO/Virgo/KAGRA S250904ae: Identification of a GW compact binary merger candidate
  10. GRB 250903A: EP-FXT counterpart detection
  11. GRB 250902A: GECAM-B detection
  12. GRB 250903A: LCO optical observation
  13. GRB 250903A: LCO optical afterglow detection
  14. GRB 250903A: SVOM/VT optical confirmation with VHF data
  15. EP250903a: SVOM/VT optical confirmation
  16. EP250901a: Mondy, Assy and SAO RAS optical limits
  17. Subject GRB 250903A: SVOM/MXT afterglow detection
  18. EP250903a: LCO candidate counterpart discovery
  19. GRB 250903A: TRT optical counterpart detection
  20. GRB 250902B: AstroSat CZTI detection
  21. GRB 250903A: SVOM detection of a burst
  22. EP250903a: Global MASTER-Net observations report
  23. EP250903a: TRT optical observations
  24. EP250903a: Einstein Probe detection of an X-ray transient
  25. EP 250827B: Detection of supernova counterpart by LCO.
  26. EP/WXT01709201159: GOTO optical follow-up
  27. EP250827b / AT 2025wkm: TRT optical observations
  28. EP250827b: NOT spectroscopic observations and AT 2025wkm classification as a broad-lined type-Ic supernova
  29. EP250827b: continued Liverpool Telescope observations
  30. GRB 250902B: SVOM/GRM observation
  31. EP250827b: SVOM/VT observation of AT 2025wkm
  32. LIGO/VIRGO/KAGRA S250818k: No evidence for radio variability of AT2025ulz in MeerKAT 3 GHz data
  33. GRB 250831A (SVOM trigger sb25083102): KAIT confirmation of stellar flare
  34. Fermi GRB 250902B: Global MASTER-Net observations report
  35. Fermi-LAT Gamma-ray Observations of IceCube-250831A
  36. GRB 250902A: Fermi GBM Detection
  37. GRB 250901A: Swift/UVOT Upper Limit
  38. GRB 250902B: Fermi GBM Final Real-time Localization
  39. IceCube-250831A: Upper limits from a search for additional neutrino events in IceCube
  40. GRB 250830B: Swift-XRT afterglow detection
  41. LIGO/Virgo/KAGRA S250902av: 1 counterpart neutrino candidate event from an IceCube neutrino search
  42. LIGO/Virgo/KAGRA S250901cb: Updated Sky localization
  43. EP250827b: Liverpool Telescope observations
  44. GRB 250831A (SVOM trigger sb25083102): confirmation of a stellar flare by SVOM/VT
  45. GRB 250902A: SVOM/GRM observation
  46. EP250828a: Early near-infrared follow-up with MIRAGE on the MDM 1.3m telescope
  47. EP250901a: refined analysis of the EP-WXT and EP-FXT observations
  48. GRB 250901A: EP-FXT follow-up observation
  49. GRB 250901A: NOT optical observations
  50. GRB 250902A: Fermi GBM Final Real-time Localization
  51. IceCube-Cascade 250828A: Upper limits from a search for additional neutrino events in IceCube
  52. GRB 250901A: SVOM/VT optical afterglow with VHF data
  53. GRB 250901A: Swift-XRT afterglow detection
  54. EP250901a: Swift-XRT observations
  55. LIGO/Virgo/KAGRA S250830bp: DECam GW-MMADS candidates
  56. GRB 250901A: LCO optical upper limit
  57. EP250827b: Swift observations of AT 2025wkm
  58. LIGO/Virgo/KAGRA S250830bp: DECam DESGW Epoch 1 Candidates
  59. EP250827b: Gemini Spectroscopy of AT 2025wkm
  60. LIGO/Virgo/KAGRA S250901cb: Identification of a GW compact binary merger candidate
  61. EP250831a: NOT optical observations and tentative afterglow candidate
  62. EP250827b: FTW Observations of AT 2025wkm
  63. EP250827b: Contemporaneous detection of EP X-ray flare EP250827b and ZTF transient ZTF25abmpngy/AT2025wkm
  64. GRB 250901A: SVOM detection of a burst
  65. GRB 250831B: SVOM/GRM observation
  66. GRB 250830C: Insight-HXMT detection
  67. EP250901a: Mephisto optical upper limits
  68. GRB 250830C: GECAM-B detection
  69. EP250901a: Global MASTER-Net observations report
  70. GRB 250830C: AstroSat CZTI detection of a long burst
  71. EP250901a: Einstein Probe detection of an X-ray transient
  72. LIGO/Virgo/KAGRA S250830m: Updated Sky localization
  73. EP250831a: EP-FXT follow-up observation
  74. EP250831a: Swift-XRT observations
  75. LIGO/Virgo/KAGRA S250831cc: Coverage and upper limits from MAXI/GSC observations
  76. IceCube Alert 250831.75: Global MASTER-Net observations report
  77. EP250831a: Global MASTER-Net observations report
  78. IceCube-250831A - IceCube observation of a high-energy neutrino candidate track-like event
  79. EP250831a: EP-WXT detection of a fast X-ray transient
  80. GRB 250831A (SVOM trigger sb25083102) is likely an outburst from star G 272-61
  81. GRB 250831A: Swift-XRT counterpart detection
  82. GRB 250831A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  83. GRB 250831A: SVOM/VT upper limit with VHF data
  84. GRB 250831A: SVOM detection of a soft burst
  85. GRB 250830B: Swift-XRT observations
  86. EP250830a: Global MASTER-Net observations report
  87. EP250830a/GRB 250830B: Einstein Probe detection of an X-ray transient and Swift/XRT follow-up
  88. LIGO/Virgo/KAGRA S250830bp: Coverage and upper limits from MAXI/GSC observations
  89. LIGO/Virgo/KAGRA S250830bp GLADEnet Completeness: Potential Host Galaxies in the 90% Credible Volume
  90. LIGO/Virgo/KAGRA S250830bp: NED Galaxies in the 4-Update Localization Volume
  91. LIGO/Virgo/KAGRA S250830bp: Updated Sky localization, EM Bright Classification, and Source Classification
  92. LIGO/Virgo/KAGRA S250830bp: Identification of a GW compact binary merger candidate
  93. EP-WXT trigger 01709200994: Liverpool Telescope upper limits
  94. GRB 250830B: Swift ToO observations
  95. EP-WXT trigger 01709200994: confirmation of a stellar flare by BOOTES-6
  96. GRB 250830B: MAXI/GSC detection
  97. LIGO/Virgo/KAGRA S250830m: Identification of a GW compact binary merger candidate
  98. GRB 250830A / MAXI J0853+337: MAXI/GSC detection
  99. The EP-WXT trigger 01709200994 is likely a flaring star
  100. GRB 250828B: Swift-BAT refined analysis

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