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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. EP250827b: Liverpool Telescope observations
  2. GRB 250831A (SVOM trigger sb25083102): confirmation of a stellar flare by SVOM/VT
  3. GRB 250902A: SVOM/GRM observation
  4. EP250828a: Early near-infrared follow-up with MIRAGE on the MDM 1.3m telescope
  5. EP250901a: refined analysis of the EP-WXT and EP-FXT observations
  6. GRB 250901A: EP-FXT follow-up observation
  7. GRB 250901A: NOT optical observations
  8. GRB 250902A: Fermi GBM Final Real-time Localization
  9. IceCube-Cascade 250828A: Upper limits from a search for additional neutrino events in IceCube
  10. GRB 250901A: SVOM/VT optical afterglow with VHF data
  11. GRB 250901A: Swift-XRT afterglow detection
  12. EP250901a: Swift-XRT observations
  13. LIGO/Virgo/KAGRA S250830bp: DECam GW-MMADS candidates
  14. GRB 250901A: LCO optical upper limit
  15. EP250827b: Swift observations of AT 2025wkm
  16. LIGO/Virgo/KAGRA S250830bp: DECam DESGW Epoch 1 Candidates
  17. EP250827b: Gemini Spectroscopy of AT 2025wkm
  18. LIGO/Virgo/KAGRA S250901cb: Identification of a GW compact binary merger candidate
  19. EP250831a: NOT optical observations and tentative afterglow candidate
  20. EP250827b: FTW Observations of AT 2025wkm
  21. EP250827b: Contemporaneous detection of EP X-ray flare EP250827b and ZTF transient ZTF25abmpngy/AT2025wkm
  22. GRB 250901A: SVOM detection of a burst
  23. GRB 250831B: SVOM/GRM observation
  24. GRB 250830C: Insight-HXMT detection
  25. EP250901a: Mephisto optical upper limits
  26. GRB 250830C: GECAM-B detection
  27. EP250901a: Global MASTER-Net observations report
  28. GRB 250830C: AstroSat CZTI detection of a long burst
  29. EP250901a: Einstein Probe detection of an X-ray transient
  30. LIGO/Virgo/KAGRA S250830m: Updated Sky localization
  31. EP250831a: EP-FXT follow-up observation
  32. EP250831a: Swift-XRT observations
  33. LIGO/Virgo/KAGRA S250831cc: Coverage and upper limits from MAXI/GSC observations
  34. IceCube Alert 250831.75: Global MASTER-Net observations report
  35. EP250831a: Global MASTER-Net observations report
  36. IceCube-250831A - IceCube observation of a high-energy neutrino candidate track-like event
  37. EP250831a: EP-WXT detection of a fast X-ray transient
  38. GRB 250831A (SVOM trigger sb25083102) is likely an outburst from star G 272-61
  39. GRB 250831A: Swift-XRT counterpart detection
  40. GRB 250831A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  41. GRB 250831A: SVOM/VT upper limit with VHF data
  42. GRB 250831A: SVOM detection of a soft burst
  43. GRB 250830B: Swift-XRT observations
  44. EP250830a: Global MASTER-Net observations report
  45. EP250830a/GRB 250830B: Einstein Probe detection of an X-ray transient and Swift/XRT follow-up
  46. LIGO/Virgo/KAGRA S250830bp: Coverage and upper limits from MAXI/GSC observations
  47. LIGO/Virgo/KAGRA S250830bp GLADEnet Completeness: Potential Host Galaxies in the 90% Credible Volume
  48. LIGO/Virgo/KAGRA S250830bp: NED Galaxies in the 4-Update Localization Volume
  49. LIGO/Virgo/KAGRA S250830bp: Updated Sky localization, EM Bright Classification, and Source Classification
  50. LIGO/Virgo/KAGRA S250830bp: Identification of a GW compact binary merger candidate
  51. EP-WXT trigger 01709200994: Liverpool Telescope upper limits
  52. GRB 250830B: Swift ToO observations
  53. EP-WXT trigger 01709200994: confirmation of a stellar flare by BOOTES-6
  54. GRB 250830B: MAXI/GSC detection
  55. LIGO/Virgo/KAGRA S250830m: Identification of a GW compact binary merger candidate
  56. GRB 250830A / MAXI J0853+337: MAXI/GSC detection
  57. The EP-WXT trigger 01709200994 is likely a flaring star
  58. GRB 250828B: Swift-BAT refined analysis
  59. EP250821a: SOAR observations
  60. EP250827a: very early ATLAS detections, starting 43 sec after the EP trigger
  61. LIGO/Virgo/KAGRA S250725j: Observations with the NSF-DOE Vera C. Rubin Observatory
  62. LIGO/Virgo/KAGRA S250818k: MeerKAT detection of an increase in radio flux from AT2025ulz
  63. GRB 250808B: SVOM detection of a burst through offline search
  64. EP250828a: refined analysis of the EP-WXT and EP-FXT observations
  65. EP250828a: Optical counterpart detection with Kinder observations
  66. EP250828a: Liverpool Telescope upper limits
  67. Swift GRB 250828B: Global MASTER-Net observations report
  68. EP250828a: Global MASTER-Net observations report
  69. EP-WXT trigger 01709200800 : KAIT optical observations
  70. EP250828a: KAIT optical upper limit
  71. EP250827a: Swift/UVOT Detection
  72. EP250828a: NOT optical counterpart confirmation
  73. EP250828a: SVOM/VT optical candidate
  74. EP250828a: Seimei/TriCCS optical counterpart detection
  75. GRB 250828B: Swift detection of a burst
  76. EP250827a: STEP/T80S Confirmation of fading optical counterpart
  77. EP250828a: Optical upper limit with Kinder observations
  78. LIGO/Virgo/KAGRA S250827fo: Updated Sky localization
  79. LIGO/Virgo/KAGRA S250818k: uGMRT 1.3 GHz observations of AT2025ulz
  80. EP250827a: LCO observations show fading optical counterpart
  81. GRB 250828A: Fermi GBM Final Localization
  82. EP250828a: Einstein Probe detection of an X-ray transient
  83. EP250827a: Preliminary analysis of the EP-WXT and EP-FXT observations
  84. GRID detection of GRB 250824A
  85. LIGO/Virgo/KAGRA S250827fo: Identification of a GW compact binary merger candidate
  86. EP250827A: VLT/X-shooter redshift confirmation
  87. Fermi GRB 250827A: Global MASTER-Net observations report
  88. EP250827a: confirmation of optical rebrightening with LCO
  89. EP250827a: GOTO observation of the optical afterglow
  90. GRB 250826A: SVOM/GRM observation
  91. GRB 250827A: Fermi GBM Final Real-time Localization
  92. EP250827A: An optical rebrightening was detected by LCO.
  93. EP250827a: Swift-XRT counterpart detection
  94. LIGO/Virgo/KAGRA S250827l: Updated Sky localization
  95. The EP-WXT trigger 01709200800 is likely a flaring star
  96. EP250827a: TRT optical observations
  97. EP250827a: BOOTES-7 early optical dectection
  98. EP250827a / GRB 250827A: MASTER-OAFA OT observation
  99. EP250827a: Gemini-South redshift z = 1.613
  100. EP250827a: Global MASTER-Net observations report

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