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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. LIGO/Virgo/KAGRA S250830bp: Identification of a GW compact binary merger candidate
  2. EP-WXT trigger 01709200994: Liverpool Telescope upper limits
  3. GRB 250830B: Swift ToO observations
  4. EP-WXT trigger 01709200994: confirmation of a stellar flare by BOOTES-6
  5. GRB 250830B: MAXI/GSC detection
  6. LIGO/Virgo/KAGRA S250830m: Identification of a GW compact binary merger candidate
  7. GRB 250830A / MAXI J0853+337: MAXI/GSC detection
  8. The EP-WXT trigger 01709200994 is likely a flaring star
  9. GRB 250828B: Swift-BAT refined analysis
  10. EP250821a: SOAR observations
  11. EP250827a: very early ATLAS detections, starting 43 sec after the EP trigger
  12. LIGO/Virgo/KAGRA S250725j: Observations with the NSF-DOE Vera C. Rubin Observatory
  13. LIGO/Virgo/KAGRA S250818k: MeerKAT detection of an increase in radio flux from AT2025ulz
  14. GRB 250808B: SVOM detection of a burst through offline search
  15. EP250828a: refined analysis of the EP-WXT and EP-FXT observations
  16. EP250828a: Optical counterpart detection with Kinder observations
  17. EP250828a: Liverpool Telescope upper limits
  18. Swift GRB 250828B: Global MASTER-Net observations report
  19. EP250828a: Global MASTER-Net observations report
  20. EP-WXT trigger 01709200800 : KAIT optical observations
  21. EP250828a: KAIT optical upper limit
  22. EP250827a: Swift/UVOT Detection
  23. EP250828a: NOT optical counterpart confirmation
  24. EP250828a: SVOM/VT optical candidate
  25. EP250828a: Seimei/TriCCS optical counterpart detection
  26. GRB 250828B: Swift detection of a burst
  27. EP250827a: STEP/T80S Confirmation of fading optical counterpart
  28. EP250828a: Optical upper limit with Kinder observations
  29. LIGO/Virgo/KAGRA S250827fo: Updated Sky localization
  30. LIGO/Virgo/KAGRA S250818k: uGMRT 1.3 GHz observations of AT2025ulz
  31. EP250827a: LCO observations show fading optical counterpart
  32. GRB 250828A: Fermi GBM Final Localization
  33. EP250828a: Einstein Probe detection of an X-ray transient
  34. EP250827a: Preliminary analysis of the EP-WXT and EP-FXT observations
  35. GRID detection of GRB 250824A
  36. LIGO/Virgo/KAGRA S250827fo: Identification of a GW compact binary merger candidate
  37. EP250827A: VLT/X-shooter redshift confirmation
  38. Fermi GRB 250827A: Global MASTER-Net observations report
  39. EP250827a: confirmation of optical rebrightening with LCO
  40. EP250827a: GOTO observation of the optical afterglow
  41. GRB 250826A: SVOM/GRM observation
  42. GRB 250827A: Fermi GBM Final Real-time Localization
  43. EP250827A: An optical rebrightening was detected by LCO.
  44. EP250827a: Swift-XRT counterpart detection
  45. LIGO/Virgo/KAGRA S250827l: Updated Sky localization
  46. The EP-WXT trigger 01709200800 is likely a flaring star
  47. EP250827a: TRT optical observations
  48. EP250827a: BOOTES-7 early optical dectection
  49. EP250827a / GRB 250827A: MASTER-OAFA OT observation
  50. EP250827a: Gemini-South redshift z = 1.613
  51. EP250827a: Global MASTER-Net observations report
  52. EP250827a: Las Cumbres independent detection of the optical counterpart
  53. EP250827a: Gemini-South optical counterpart detection
  54. EP250827a: Einstein Probe detection of an X-ray transient
  55. LIGO/Virgo/KAGRA S250827l: Identification of a GW compact binary merger candidate
  56. Fermi GRB 250826A: Global MASTER-Net observations report
  57. GRB 250806A: HiPERCAM/GTC limits on a possible supernova
  58. EP250821a: Gemini GMOS Redshift Confirmation
  59. LIGO/Virgo/KAGRA S250818k: SAO RAS BTA z-band observations of AT2025ulz
  60. Fermi trigger No 777883624: Global MASTER-Net observations report
  61. Fermi Gamma-ray Burst Monitor trigger 777883624/250826283 is not a GRB
  62. GRB 250826A: Fermi GBM Final Real-time Localization
  63. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Confirmation of Rebrightening of AT2025ulz
  64. Fermi GRB 250824B: Global MASTER-Net observations report
  65. LIGO/Virgo/KAGRA S250818k: VLA upper limits on AT2025ulz
  66. LIGO/Virgo/KAGRA S250818k: nature of the AT2025ulz/ZTF25abjmnnps OT
  67. LIGO/Virgo/KAGRA S250818k: Pan-STARRS imaging confirms re-brightening of SN2025ulz
  68. GRB 250823A: Swift-BAT refined analysis
  69. LIGO/Virgo/KAGRA S250818k: Continued Keck I LRIS spectroscopy of ZTF25abjmnps (AT2025ulz)
  70. GRB 250821B: AstroSat CZTI detection
  71. GRB 250819A: AstroSat CZTI detection
  72. LIGO/Virgo/KAGRA S250818k: FTW Observations Show Continued Reddening of AT 2025ulz
  73. LIGO/Virgo/KAGRA S250818k: MASTER predicovery limits of the AT2025ulz/ZTF25abjmnps KN candidate
  74. GRB 250821B: Insight-HXMT detection
  75. LIGO/Virgo/KAGRA S250818k: ENGRAVE observations of SN 2025ulz as a type II supernova
  76. GRB 250823A: Swift-XRT refined Analysis
  77. EP250821a: MeerKAT radio counterpart
  78. EP triggers 01709200706 and 01709200707: GOTO confirmation of flaring stars
  79. LIGO/Virgo/KAGRA S250818k: Swift Observations of AT 2025ulz - Second Epoch
  80. GRB 250824B: Fermi GBM Final Real-time Localization
  81. The EP-WXT trigger 01709200707 is likely a flaring star
  82. GRB 250823A: COLIBRÍ optical observations
  83. The EP-WXT trigger 01709200706 is likely a flaring star
  84. GRB 250823A: SVOM/VT optical observation
  85. GRB 250824A: Fermi GBM Final Real-time Localization
  86. GRB 250823A: Swift/UVOT Detection
  87. GRB 250823A: NOT optical observations
  88. LIGO/Virgo/KAGRA S250818k: CFH/MegaCam follow-up observation for AT2025ulz
  89. LIGO/Virgo/KAGRA S250818k: COLIBRÍ confirmation of rebrightening of AT2025ulz
  90. GRB 250823A: Fermi GBM Observation
  91. GRB 250818B: MeerKAT Detection
  92. GRB 250823A: Enhanced Swift-XRT position
  93. GRB 250823A: LCOGT Optical Detection
  94. GRB 250823A: BOOTES6/DPRT early optical detection
  95. GRB 250823A: Liverpool Telescope optical detection
  96. GRB 250823A: Swift detection of a burst
  97. GRB 250823A: Fermi GBM Final Real-time Localization
  98. Swift GRB250823.84: Global MASTER-Net observations report
  99. Konus-Wind detection of GRB 250821B
  100. LIGO/Virgo/KAGRA S250818k: Rebrightening detected with Gemini/GMOS

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