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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 250902A: GECAM-B detection
  2. GRB 250903A: LCO optical observation
  3. GRB 250903A: LCO optical afterglow detection
  4. GRB 250903A: SVOM/VT optical confirmation with VHF data
  5. EP250903a: SVOM/VT optical confirmation
  6. EP250901a: Mondy, Assy and SAO RAS optical limits
  7. Subject GRB 250903A: SVOM/MXT afterglow detection
  8. EP250903a: LCO candidate counterpart discovery
  9. GRB 250903A: TRT optical counterpart detection
  10. GRB 250902B: AstroSat CZTI detection
  11. GRB 250903A: SVOM detection of a burst
  12. EP250903a: Global MASTER-Net observations report
  13. EP250903a: TRT optical observations
  14. EP250903a: Einstein Probe detection of an X-ray transient
  15. EP 250827B: Detection of supernova counterpart by LCO.
  16. EP/WXT01709201159: GOTO optical follow-up
  17. EP250827b / AT 2025wkm: TRT optical observations
  18. EP250827b: NOT spectroscopic observations and AT 2025wkm classification as a broad-lined type-Ic supernova
  19. EP250827b: continued Liverpool Telescope observations
  20. GRB 250902B: SVOM/GRM observation
  21. EP250827b: SVOM/VT observation of AT 2025wkm
  22. LIGO/VIRGO/KAGRA S250818k: No evidence for radio variability of AT2025ulz in MeerKAT 3 GHz data
  23. GRB 250831A (SVOM trigger sb25083102): KAIT confirmation of stellar flare
  24. Fermi GRB 250902B: Global MASTER-Net observations report
  25. Fermi-LAT Gamma-ray Observations of IceCube-250831A
  26. GRB 250902A: Fermi GBM Detection
  27. GRB 250901A: Swift/UVOT Upper Limit
  28. GRB 250902B: Fermi GBM Final Real-time Localization
  29. IceCube-250831A: Upper limits from a search for additional neutrino events in IceCube
  30. GRB 250830B: Swift-XRT afterglow detection
  31. LIGO/Virgo/KAGRA S250902av: 1 counterpart neutrino candidate event from an IceCube neutrino search
  32. LIGO/Virgo/KAGRA S250901cb: Updated Sky localization
  33. EP250827b: Liverpool Telescope observations
  34. GRB 250831A (SVOM trigger sb25083102): confirmation of a stellar flare by SVOM/VT
  35. GRB 250902A: SVOM/GRM observation
  36. EP250828a: Early near-infrared follow-up with MIRAGE on the MDM 1.3m telescope
  37. EP250901a: refined analysis of the EP-WXT and EP-FXT observations
  38. GRB 250901A: EP-FXT follow-up observation
  39. GRB 250901A: NOT optical observations
  40. GRB 250902A: Fermi GBM Final Real-time Localization
  41. IceCube-Cascade 250828A: Upper limits from a search for additional neutrino events in IceCube
  42. GRB 250901A: SVOM/VT optical afterglow with VHF data
  43. GRB 250901A: Swift-XRT afterglow detection
  44. EP250901a: Swift-XRT observations
  45. LIGO/Virgo/KAGRA S250830bp: DECam GW-MMADS candidates
  46. GRB 250901A: LCO optical upper limit
  47. EP250827b: Swift observations of AT 2025wkm
  48. LIGO/Virgo/KAGRA S250830bp: DECam DESGW Epoch 1 Candidates
  49. EP250827b: Gemini Spectroscopy of AT 2025wkm
  50. LIGO/Virgo/KAGRA S250901cb: Identification of a GW compact binary merger candidate
  51. EP250831a: NOT optical observations and tentative afterglow candidate
  52. EP250827b: FTW Observations of AT 2025wkm
  53. EP250827b: Contemporaneous detection of EP X-ray flare EP250827b and ZTF transient ZTF25abmpngy/AT2025wkm
  54. GRB 250901A: SVOM detection of a burst
  55. GRB 250831B: SVOM/GRM observation
  56. GRB 250830C: Insight-HXMT detection
  57. EP250901a: Mephisto optical upper limits
  58. GRB 250830C: GECAM-B detection
  59. EP250901a: Global MASTER-Net observations report
  60. GRB 250830C: AstroSat CZTI detection of a long burst
  61. EP250901a: Einstein Probe detection of an X-ray transient
  62. LIGO/Virgo/KAGRA S250830m: Updated Sky localization
  63. EP250831a: EP-FXT follow-up observation
  64. EP250831a: Swift-XRT observations
  65. LIGO/Virgo/KAGRA S250831cc: Coverage and upper limits from MAXI/GSC observations
  66. IceCube Alert 250831.75: Global MASTER-Net observations report
  67. EP250831a: Global MASTER-Net observations report
  68. IceCube-250831A - IceCube observation of a high-energy neutrino candidate track-like event
  69. EP250831a: EP-WXT detection of a fast X-ray transient
  70. GRB 250831A (SVOM trigger sb25083102) is likely an outburst from star G 272-61
  71. GRB 250831A: Swift-XRT counterpart detection
  72. GRB 250831A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  73. GRB 250831A: SVOM/VT upper limit with VHF data
  74. GRB 250831A: SVOM detection of a soft burst
  75. GRB 250830B: Swift-XRT observations
  76. EP250830a: Global MASTER-Net observations report
  77. EP250830a/GRB 250830B: Einstein Probe detection of an X-ray transient and Swift/XRT follow-up
  78. LIGO/Virgo/KAGRA S250830bp: Coverage and upper limits from MAXI/GSC observations
  79. LIGO/Virgo/KAGRA S250830bp GLADEnet Completeness: Potential Host Galaxies in the 90% Credible Volume
  80. LIGO/Virgo/KAGRA S250830bp: NED Galaxies in the 4-Update Localization Volume
  81. LIGO/Virgo/KAGRA S250830bp: Updated Sky localization, EM Bright Classification, and Source Classification
  82. LIGO/Virgo/KAGRA S250830bp: Identification of a GW compact binary merger candidate
  83. EP-WXT trigger 01709200994: Liverpool Telescope upper limits
  84. GRB 250830B: Swift ToO observations
  85. EP-WXT trigger 01709200994: confirmation of a stellar flare by BOOTES-6
  86. GRB 250830B: MAXI/GSC detection
  87. LIGO/Virgo/KAGRA S250830m: Identification of a GW compact binary merger candidate
  88. GRB 250830A / MAXI J0853+337: MAXI/GSC detection
  89. The EP-WXT trigger 01709200994 is likely a flaring star
  90. GRB 250828B: Swift-BAT refined analysis
  91. EP250821a: SOAR observations
  92. EP250827a: very early ATLAS detections, starting 43 sec after the EP trigger
  93. LIGO/Virgo/KAGRA S250725j: Observations with the NSF-DOE Vera C. Rubin Observatory
  94. LIGO/Virgo/KAGRA S250818k: MeerKAT detection of an increase in radio flux from AT2025ulz
  95. GRB 250808B: SVOM detection of a burst through offline search
  96. EP250828a: refined analysis of the EP-WXT and EP-FXT observations
  97. EP250828a: Optical counterpart detection with Kinder observations
  98. EP250828a: Liverpool Telescope upper limits
  99. Swift GRB 250828B: Global MASTER-Net observations report
  100. EP250828a: Global MASTER-Net observations report

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