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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: Contemporaneous detection of EP X-ray flare EP250827b and ZTF transient ZTF25abmpngy/AT2025wkm
  2. GRB 250901A: SVOM detection of a burst
  3. GRB 250831B: SVOM/GRM observation
  4. GRB 250830C: Insight-HXMT detection
  5. EP250901a: Mephisto optical upper limits
  6. GRB 250830C: GECAM-B detection
  7. EP250901a: Global MASTER-Net observations report
  8. GRB 250830C: AstroSat CZTI detection of a long burst
  9. EP250901a: Einstein Probe detection of an X-ray transient
  10. LIGO/Virgo/KAGRA S250830m: Updated Sky localization
  11. EP250831a: EP-FXT follow-up observation
  12. EP250831a: Swift-XRT observations
  13. LIGO/Virgo/KAGRA S250831cc: Coverage and upper limits from MAXI/GSC observations
  14. IceCube Alert 250831.75: Global MASTER-Net observations report
  15. EP250831a: Global MASTER-Net observations report
  16. IceCube-250831A - IceCube observation of a high-energy neutrino candidate track-like event
  17. EP250831a: EP-WXT detection of a fast X-ray transient
  18. GRB 250831A (SVOM trigger sb25083102) is likely an outburst from star G 272-61
  19. GRB 250831A: Swift-XRT counterpart detection
  20. GRB 250831A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  21. GRB 250831A: SVOM/VT upper limit with VHF data
  22. GRB 250831A: SVOM detection of a soft burst
  23. GRB 250830B: Swift-XRT observations
  24. EP250830a: Global MASTER-Net observations report
  25. EP250830a/GRB 250830B: Einstein Probe detection of an X-ray transient and Swift/XRT follow-up
  26. LIGO/Virgo/KAGRA S250830bp: Coverage and upper limits from MAXI/GSC observations
  27. LIGO/Virgo/KAGRA S250830bp GLADEnet Completeness: Potential Host Galaxies in the 90% Credible Volume
  28. LIGO/Virgo/KAGRA S250830bp: NED Galaxies in the 4-Update Localization Volume
  29. LIGO/Virgo/KAGRA S250830bp: Updated Sky localization, EM Bright Classification, and Source Classification
  30. LIGO/Virgo/KAGRA S250830bp: Identification of a GW compact binary merger candidate
  31. EP-WXT trigger 01709200994: Liverpool Telescope upper limits
  32. GRB 250830B: Swift ToO observations
  33. EP-WXT trigger 01709200994: confirmation of a stellar flare by BOOTES-6
  34. GRB 250830B: MAXI/GSC detection
  35. LIGO/Virgo/KAGRA S250830m: Identification of a GW compact binary merger candidate
  36. GRB 250830A / MAXI J0853+337: MAXI/GSC detection
  37. The EP-WXT trigger 01709200994 is likely a flaring star
  38. GRB 250828B: Swift-BAT refined analysis
  39. EP250821a: SOAR observations
  40. EP250827a: very early ATLAS detections, starting 43 sec after the EP trigger
  41. LIGO/Virgo/KAGRA S250725j: Observations with the NSF-DOE Vera C. Rubin Observatory
  42. LIGO/Virgo/KAGRA S250818k: MeerKAT detection of an increase in radio flux from AT2025ulz
  43. GRB 250808B: SVOM detection of a burst through offline search
  44. EP250828a: refined analysis of the EP-WXT and EP-FXT observations
  45. EP250828a: Optical counterpart detection with Kinder observations
  46. EP250828a: Liverpool Telescope upper limits
  47. Swift GRB 250828B: Global MASTER-Net observations report
  48. EP250828a: Global MASTER-Net observations report
  49. EP-WXT trigger 01709200800 : KAIT optical observations
  50. EP250828a: KAIT optical upper limit
  51. EP250827a: Swift/UVOT Detection
  52. EP250828a: NOT optical counterpart confirmation
  53. EP250828a: SVOM/VT optical candidate
  54. EP250828a: Seimei/TriCCS optical counterpart detection
  55. GRB 250828B: Swift detection of a burst
  56. EP250827a: STEP/T80S Confirmation of fading optical counterpart
  57. EP250828a: Optical upper limit with Kinder observations
  58. LIGO/Virgo/KAGRA S250827fo: Updated Sky localization
  59. LIGO/Virgo/KAGRA S250818k: uGMRT 1.3 GHz observations of AT2025ulz
  60. EP250827a: LCO observations show fading optical counterpart
  61. GRB 250828A: Fermi GBM Final Localization
  62. EP250828a: Einstein Probe detection of an X-ray transient
  63. EP250827a: Preliminary analysis of the EP-WXT and EP-FXT observations
  64. GRID detection of GRB 250824A
  65. LIGO/Virgo/KAGRA S250827fo: Identification of a GW compact binary merger candidate
  66. EP250827A: VLT/X-shooter redshift confirmation
  67. Fermi GRB 250827A: Global MASTER-Net observations report
  68. EP250827a: confirmation of optical rebrightening with LCO
  69. EP250827a: GOTO observation of the optical afterglow
  70. GRB 250826A: SVOM/GRM observation
  71. GRB 250827A: Fermi GBM Final Real-time Localization
  72. EP250827A: An optical rebrightening was detected by LCO.
  73. EP250827a: Swift-XRT counterpart detection
  74. LIGO/Virgo/KAGRA S250827l: Updated Sky localization
  75. The EP-WXT trigger 01709200800 is likely a flaring star
  76. EP250827a: TRT optical observations
  77. EP250827a: BOOTES-7 early optical dectection
  78. EP250827a / GRB 250827A: MASTER-OAFA OT observation
  79. EP250827a: Gemini-South redshift z = 1.613
  80. EP250827a: Global MASTER-Net observations report
  81. EP250827a: Las Cumbres independent detection of the optical counterpart
  82. EP250827a: Gemini-South optical counterpart detection
  83. EP250827a: Einstein Probe detection of an X-ray transient
  84. LIGO/Virgo/KAGRA S250827l: Identification of a GW compact binary merger candidate
  85. Fermi GRB 250826A: Global MASTER-Net observations report
  86. GRB 250806A: HiPERCAM/GTC limits on a possible supernova
  87. EP250821a: Gemini GMOS Redshift Confirmation
  88. LIGO/Virgo/KAGRA S250818k: SAO RAS BTA z-band observations of AT2025ulz
  89. Fermi trigger No 777883624: Global MASTER-Net observations report
  90. Fermi Gamma-ray Burst Monitor trigger 777883624/250826283 is not a GRB
  91. GRB 250826A: Fermi GBM Final Real-time Localization
  92. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Confirmation of Rebrightening of AT2025ulz
  93. Fermi GRB 250824B: Global MASTER-Net observations report
  94. LIGO/Virgo/KAGRA S250818k: VLA upper limits on AT2025ulz
  95. LIGO/Virgo/KAGRA S250818k: nature of the AT2025ulz/ZTF25abjmnnps OT
  96. LIGO/Virgo/KAGRA S250818k: Pan-STARRS imaging confirms re-brightening of SN2025ulz
  97. GRB 250823A: Swift-BAT refined analysis
  98. LIGO/Virgo/KAGRA S250818k: Continued Keck I LRIS spectroscopy of ZTF25abjmnps (AT2025ulz)
  99. GRB 250821B: AstroSat CZTI detection
  100. GRB 250819A: AstroSat CZTI detection

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