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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. The EP-WXT trigger 01709200994 is likely a flaring star
  2. GRB 250828B: Swift-BAT refined analysis
  3. EP250821a: SOAR observations
  4. EP250827a: very early ATLAS detections, starting 43 sec after the EP trigger
  5. LIGO/Virgo/KAGRA S250725j: Observations with the NSF-DOE Vera C. Rubin Observatory
  6. LIGO/Virgo/KAGRA S250818k: MeerKAT detection of an increase in radio flux from AT2025ulz
  7. GRB 250808B: SVOM detection of a burst through offline search
  8. EP250828a: refined analysis of the EP-WXT and EP-FXT observations
  9. EP250828a: Optical counterpart detection with Kinder observations
  10. EP250828a: Liverpool Telescope upper limits
  11. Swift GRB 250828B: Global MASTER-Net observations report
  12. EP250828a: Global MASTER-Net observations report
  13. EP-WXT trigger 01709200800 : KAIT optical observations
  14. EP250828a: KAIT optical upper limit
  15. EP250827a: Swift/UVOT Detection
  16. EP250828a: NOT optical counterpart confirmation
  17. EP250828a: SVOM/VT optical candidate
  18. EP250828a: Seimei/TriCCS optical counterpart detection
  19. GRB 250828B: Swift detection of a burst
  20. EP250827a: STEP/T80S Confirmation of fading optical counterpart
  21. EP250828a: Optical upper limit with Kinder observations
  22. LIGO/Virgo/KAGRA S250827fo: Updated Sky localization
  23. LIGO/Virgo/KAGRA S250818k: uGMRT 1.3 GHz observations of AT2025ulz
  24. EP250827a: LCO observations show fading optical counterpart
  25. GRB 250828A: Fermi GBM Final Localization
  26. EP250828a: Einstein Probe detection of an X-ray transient
  27. EP250827a: Preliminary analysis of the EP-WXT and EP-FXT observations
  28. GRID detection of GRB 250824A
  29. LIGO/Virgo/KAGRA S250827fo: Identification of a GW compact binary merger candidate
  30. EP250827A: VLT/X-shooter redshift confirmation
  31. Fermi GRB 250827A: Global MASTER-Net observations report
  32. EP250827a: confirmation of optical rebrightening with LCO
  33. EP250827a: GOTO observation of the optical afterglow
  34. GRB 250826A: SVOM/GRM observation
  35. GRB 250827A: Fermi GBM Final Real-time Localization
  36. EP250827A: An optical rebrightening was detected by LCO.
  37. EP250827a: Swift-XRT counterpart detection
  38. LIGO/Virgo/KAGRA S250827l: Updated Sky localization
  39. The EP-WXT trigger 01709200800 is likely a flaring star
  40. EP250827a: TRT optical observations
  41. EP250827a: BOOTES-7 early optical dectection
  42. EP250827a / GRB 250827A: MASTER-OAFA OT observation
  43. EP250827a: Gemini-South redshift z = 1.613
  44. EP250827a: Global MASTER-Net observations report
  45. EP250827a: Las Cumbres independent detection of the optical counterpart
  46. EP250827a: Gemini-South optical counterpart detection
  47. EP250827a: Einstein Probe detection of an X-ray transient
  48. LIGO/Virgo/KAGRA S250827l: Identification of a GW compact binary merger candidate
  49. Fermi GRB 250826A: Global MASTER-Net observations report
  50. GRB 250806A: HiPERCAM/GTC limits on a possible supernova
  51. EP250821a: Gemini GMOS Redshift Confirmation
  52. LIGO/Virgo/KAGRA S250818k: SAO RAS BTA z-band observations of AT2025ulz
  53. Fermi trigger No 777883624: Global MASTER-Net observations report
  54. Fermi Gamma-ray Burst Monitor trigger 777883624/250826283 is not a GRB
  55. GRB 250826A: Fermi GBM Final Real-time Localization
  56. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Confirmation of Rebrightening of AT2025ulz
  57. Fermi GRB 250824B: Global MASTER-Net observations report
  58. LIGO/Virgo/KAGRA S250818k: VLA upper limits on AT2025ulz
  59. LIGO/Virgo/KAGRA S250818k: nature of the AT2025ulz/ZTF25abjmnnps OT
  60. LIGO/Virgo/KAGRA S250818k: Pan-STARRS imaging confirms re-brightening of SN2025ulz
  61. GRB 250823A: Swift-BAT refined analysis
  62. LIGO/Virgo/KAGRA S250818k: Continued Keck I LRIS spectroscopy of ZTF25abjmnps (AT2025ulz)
  63. GRB 250821B: AstroSat CZTI detection
  64. GRB 250819A: AstroSat CZTI detection
  65. LIGO/Virgo/KAGRA S250818k: FTW Observations Show Continued Reddening of AT 2025ulz
  66. LIGO/Virgo/KAGRA S250818k: MASTER predicovery limits of the AT2025ulz/ZTF25abjmnps KN candidate
  67. GRB 250821B: Insight-HXMT detection
  68. LIGO/Virgo/KAGRA S250818k: ENGRAVE observations of SN 2025ulz as a type II supernova
  69. GRB 250823A: Swift-XRT refined Analysis
  70. EP250821a: MeerKAT radio counterpart
  71. EP triggers 01709200706 and 01709200707: GOTO confirmation of flaring stars
  72. LIGO/Virgo/KAGRA S250818k: Swift Observations of AT 2025ulz - Second Epoch
  73. GRB 250824B: Fermi GBM Final Real-time Localization
  74. The EP-WXT trigger 01709200707 is likely a flaring star
  75. GRB 250823A: COLIBRÍ optical observations
  76. The EP-WXT trigger 01709200706 is likely a flaring star
  77. GRB 250823A: SVOM/VT optical observation
  78. GRB 250824A: Fermi GBM Final Real-time Localization
  79. GRB 250823A: Swift/UVOT Detection
  80. GRB 250823A: NOT optical observations
  81. LIGO/Virgo/KAGRA S250818k: CFH/MegaCam follow-up observation for AT2025ulz
  82. LIGO/Virgo/KAGRA S250818k: COLIBRÍ confirmation of rebrightening of AT2025ulz
  83. GRB 250823A: Fermi GBM Observation
  84. GRB 250818B: MeerKAT Detection
  85. GRB 250823A: Enhanced Swift-XRT position
  86. GRB 250823A: LCOGT Optical Detection
  87. GRB 250823A: BOOTES6/DPRT early optical detection
  88. GRB 250823A: Liverpool Telescope optical detection
  89. GRB 250823A: Swift detection of a burst
  90. GRB 250823A: Fermi GBM Final Real-time Localization
  91. Swift GRB250823.84: Global MASTER-Net observations report
  92. Konus-Wind detection of GRB 250821B
  93. LIGO/Virgo/KAGRA S250818k: Rebrightening detected with Gemini/GMOS
  94. LIGO/Virgo/KAGRA S250818k: HST nIR detection of AT 2025ulz
  95. LIGO/Virgo/KAGRA S250818k: J-GEM follow-up observation for AT2025ulz
  96. LIGO/Virgo/KAGRA S250818k: PRIME nIR observations of AT2025ulz
  97. LIGO/Virgo/KAGRA S250818k: JinShan optical observations of AT2025ulz
  98. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Optical Detection of AT2025ulz
  99. LIGO/Virgo/Kagra S250818k: STEP/T80N upper limits on 2025ulz
  100. LIGO/Virgo/KAGRA S250818k: 3 GHz MeerKAT observations of AT2025ulz

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