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

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