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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: Swift observations of AT 2025wkm
  2. LIGO/Virgo/KAGRA S250830bp: DECam DESGW Epoch 1 Candidates
  3. EP250827b: Gemini Spectroscopy of AT 2025wkm
  4. LIGO/Virgo/KAGRA S250901cb: Identification of a GW compact binary merger candidate
  5. EP250831a: NOT optical observations and tentative afterglow candidate
  6. EP250827b: FTW Observations of AT 2025wkm
  7. EP250827b: Contemporaneous detection of EP X-ray flare EP250827b and ZTF transient ZTF25abmpngy/AT2025wkm
  8. GRB 250901A: SVOM detection of a burst
  9. GRB 250831B: SVOM/GRM observation
  10. GRB 250830C: Insight-HXMT detection
  11. EP250901a: Mephisto optical upper limits
  12. GRB 250830C: GECAM-B detection
  13. EP250901a: Global MASTER-Net observations report
  14. GRB 250830C: AstroSat CZTI detection of a long burst
  15. EP250901a: Einstein Probe detection of an X-ray transient
  16. LIGO/Virgo/KAGRA S250830m: Updated Sky localization
  17. EP250831a: EP-FXT follow-up observation
  18. EP250831a: Swift-XRT observations
  19. LIGO/Virgo/KAGRA S250831cc: Coverage and upper limits from MAXI/GSC observations
  20. IceCube Alert 250831.75: Global MASTER-Net observations report
  21. EP250831a: Global MASTER-Net observations report
  22. IceCube-250831A - IceCube observation of a high-energy neutrino candidate track-like event
  23. EP250831a: EP-WXT detection of a fast X-ray transient
  24. GRB 250831A (SVOM trigger sb25083102) is likely an outburst from star G 272-61
  25. GRB 250831A: Swift-XRT counterpart detection
  26. GRB 250831A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  27. GRB 250831A: SVOM/VT upper limit with VHF data
  28. GRB 250831A: SVOM detection of a soft burst
  29. GRB 250830B: Swift-XRT observations
  30. EP250830a: Global MASTER-Net observations report
  31. EP250830a/GRB 250830B: Einstein Probe detection of an X-ray transient and Swift/XRT follow-up
  32. LIGO/Virgo/KAGRA S250830bp: Coverage and upper limits from MAXI/GSC observations
  33. LIGO/Virgo/KAGRA S250830bp GLADEnet Completeness: Potential Host Galaxies in the 90% Credible Volume
  34. LIGO/Virgo/KAGRA S250830bp: NED Galaxies in the 4-Update Localization Volume
  35. LIGO/Virgo/KAGRA S250830bp: Updated Sky localization, EM Bright Classification, and Source Classification
  36. LIGO/Virgo/KAGRA S250830bp: Identification of a GW compact binary merger candidate
  37. EP-WXT trigger 01709200994: Liverpool Telescope upper limits
  38. GRB 250830B: Swift ToO observations
  39. EP-WXT trigger 01709200994: confirmation of a stellar flare by BOOTES-6
  40. GRB 250830B: MAXI/GSC detection
  41. LIGO/Virgo/KAGRA S250830m: Identification of a GW compact binary merger candidate
  42. GRB 250830A / MAXI J0853+337: MAXI/GSC detection
  43. The EP-WXT trigger 01709200994 is likely a flaring star
  44. GRB 250828B: Swift-BAT refined analysis
  45. EP250821a: SOAR observations
  46. EP250827a: very early ATLAS detections, starting 43 sec after the EP trigger
  47. LIGO/Virgo/KAGRA S250725j: Observations with the NSF-DOE Vera C. Rubin Observatory
  48. LIGO/Virgo/KAGRA S250818k: MeerKAT detection of an increase in radio flux from AT2025ulz
  49. GRB 250808B: SVOM detection of a burst through offline search
  50. EP250828a: refined analysis of the EP-WXT and EP-FXT observations
  51. EP250828a: Optical counterpart detection with Kinder observations
  52. EP250828a: Liverpool Telescope upper limits
  53. Swift GRB 250828B: Global MASTER-Net observations report
  54. EP250828a: Global MASTER-Net observations report
  55. EP-WXT trigger 01709200800 : KAIT optical observations
  56. EP250828a: KAIT optical upper limit
  57. EP250827a: Swift/UVOT Detection
  58. EP250828a: NOT optical counterpart confirmation
  59. EP250828a: SVOM/VT optical candidate
  60. EP250828a: Seimei/TriCCS optical counterpart detection
  61. GRB 250828B: Swift detection of a burst
  62. EP250827a: STEP/T80S Confirmation of fading optical counterpart
  63. EP250828a: Optical upper limit with Kinder observations
  64. LIGO/Virgo/KAGRA S250827fo: Updated Sky localization
  65. LIGO/Virgo/KAGRA S250818k: uGMRT 1.3 GHz observations of AT2025ulz
  66. EP250827a: LCO observations show fading optical counterpart
  67. GRB 250828A: Fermi GBM Final Localization
  68. EP250828a: Einstein Probe detection of an X-ray transient
  69. EP250827a: Preliminary analysis of the EP-WXT and EP-FXT observations
  70. GRID detection of GRB 250824A
  71. LIGO/Virgo/KAGRA S250827fo: Identification of a GW compact binary merger candidate
  72. EP250827A: VLT/X-shooter redshift confirmation
  73. Fermi GRB 250827A: Global MASTER-Net observations report
  74. EP250827a: confirmation of optical rebrightening with LCO
  75. EP250827a: GOTO observation of the optical afterglow
  76. GRB 250826A: SVOM/GRM observation
  77. GRB 250827A: Fermi GBM Final Real-time Localization
  78. EP250827A: An optical rebrightening was detected by LCO.
  79. EP250827a: Swift-XRT counterpart detection
  80. LIGO/Virgo/KAGRA S250827l: Updated Sky localization
  81. The EP-WXT trigger 01709200800 is likely a flaring star
  82. EP250827a: TRT optical observations
  83. EP250827a: BOOTES-7 early optical dectection
  84. EP250827a / GRB 250827A: MASTER-OAFA OT observation
  85. EP250827a: Gemini-South redshift z = 1.613
  86. EP250827a: Global MASTER-Net observations report
  87. EP250827a: Las Cumbres independent detection of the optical counterpart
  88. EP250827a: Gemini-South optical counterpart detection
  89. EP250827a: Einstein Probe detection of an X-ray transient
  90. LIGO/Virgo/KAGRA S250827l: Identification of a GW compact binary merger candidate
  91. Fermi GRB 250826A: Global MASTER-Net observations report
  92. GRB 250806A: HiPERCAM/GTC limits on a possible supernova
  93. EP250821a: Gemini GMOS Redshift Confirmation
  94. LIGO/Virgo/KAGRA S250818k: SAO RAS BTA z-band observations of AT2025ulz
  95. Fermi trigger No 777883624: Global MASTER-Net observations report
  96. Fermi Gamma-ray Burst Monitor trigger 777883624/250826283 is not a GRB
  97. GRB 250826A: Fermi GBM Final Real-time Localization
  98. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Confirmation of Rebrightening of AT2025ulz
  99. Fermi GRB 250824B: Global MASTER-Net observations report
  100. LIGO/Virgo/KAGRA S250818k: VLA upper limits on AT2025ulz

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