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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 S250818k: MeerKAT detection of an increase in radio flux from AT2025ulz
  2. GRB 250808B: SVOM detection of a burst through offline search
  3. EP250828a: refined analysis of the EP-WXT and EP-FXT observations
  4. EP250828a: Optical counterpart detection with Kinder observations
  5. EP250828a: Liverpool Telescope upper limits
  6. Swift GRB 250828B: Global MASTER-Net observations report
  7. EP250828a: Global MASTER-Net observations report
  8. EP-WXT trigger 01709200800 : KAIT optical observations
  9. EP250828a: KAIT optical upper limit
  10. EP250827a: Swift/UVOT Detection
  11. EP250828a: NOT optical counterpart confirmation
  12. EP250828a: SVOM/VT optical candidate
  13. EP250828a: Seimei/TriCCS optical counterpart detection
  14. GRB 250828B: Swift detection of a burst
  15. EP250827a: STEP/T80S Confirmation of fading optical counterpart
  16. EP250828a: Optical upper limit with Kinder observations
  17. LIGO/Virgo/KAGRA S250827fo: Updated Sky localization
  18. LIGO/Virgo/KAGRA S250818k: uGMRT 1.3 GHz observations of AT2025ulz
  19. EP250827a: LCO observations show fading optical counterpart
  20. GRB 250828A: Fermi GBM Final Localization
  21. EP250828a: Einstein Probe detection of an X-ray transient
  22. EP250827a: Preliminary analysis of the EP-WXT and EP-FXT observations
  23. GRID detection of GRB 250824A
  24. LIGO/Virgo/KAGRA S250827fo: Identification of a GW compact binary merger candidate
  25. EP250827A: VLT/X-shooter redshift confirmation
  26. Fermi GRB 250827A: Global MASTER-Net observations report
  27. EP250827a: confirmation of optical rebrightening with LCO
  28. EP250827a: GOTO observation of the optical afterglow
  29. GRB 250826A: SVOM/GRM observation
  30. GRB 250827A: Fermi GBM Final Real-time Localization
  31. EP250827A: An optical rebrightening was detected by LCO.
  32. EP250827a: Swift-XRT counterpart detection
  33. LIGO/Virgo/KAGRA S250827l: Updated Sky localization
  34. The EP-WXT trigger 01709200800 is likely a flaring star
  35. EP250827a: TRT optical observations
  36. EP250827a: BOOTES-7 early optical dectection
  37. EP250827a / GRB 250827A: MASTER-OAFA OT observation
  38. EP250827a: Gemini-South redshift z = 1.613
  39. EP250827a: Global MASTER-Net observations report
  40. EP250827a: Las Cumbres independent detection of the optical counterpart
  41. EP250827a: Gemini-South optical counterpart detection
  42. EP250827a: Einstein Probe detection of an X-ray transient
  43. LIGO/Virgo/KAGRA S250827l: Identification of a GW compact binary merger candidate
  44. Fermi GRB 250826A: Global MASTER-Net observations report
  45. GRB 250806A: HiPERCAM/GTC limits on a possible supernova
  46. EP250821a: Gemini GMOS Redshift Confirmation
  47. LIGO/Virgo/KAGRA S250818k: SAO RAS BTA z-band observations of AT2025ulz
  48. Fermi trigger No 777883624: Global MASTER-Net observations report
  49. Fermi Gamma-ray Burst Monitor trigger 777883624/250826283 is not a GRB
  50. GRB 250826A: Fermi GBM Final Real-time Localization
  51. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Confirmation of Rebrightening of AT2025ulz
  52. Fermi GRB 250824B: Global MASTER-Net observations report
  53. LIGO/Virgo/KAGRA S250818k: VLA upper limits on AT2025ulz
  54. LIGO/Virgo/KAGRA S250818k: nature of the AT2025ulz/ZTF25abjmnnps OT
  55. LIGO/Virgo/KAGRA S250818k: Pan-STARRS imaging confirms re-brightening of SN2025ulz
  56. GRB 250823A: Swift-BAT refined analysis
  57. LIGO/Virgo/KAGRA S250818k: Continued Keck I LRIS spectroscopy of ZTF25abjmnps (AT2025ulz)
  58. GRB 250821B: AstroSat CZTI detection
  59. GRB 250819A: AstroSat CZTI detection
  60. LIGO/Virgo/KAGRA S250818k: FTW Observations Show Continued Reddening of AT 2025ulz
  61. LIGO/Virgo/KAGRA S250818k: MASTER predicovery limits of the AT2025ulz/ZTF25abjmnps KN candidate
  62. GRB 250821B: Insight-HXMT detection
  63. LIGO/Virgo/KAGRA S250818k: ENGRAVE observations of SN 2025ulz as a type II supernova
  64. GRB 250823A: Swift-XRT refined Analysis
  65. EP250821a: MeerKAT radio counterpart
  66. EP triggers 01709200706 and 01709200707: GOTO confirmation of flaring stars
  67. LIGO/Virgo/KAGRA S250818k: Swift Observations of AT 2025ulz - Second Epoch
  68. GRB 250824B: Fermi GBM Final Real-time Localization
  69. The EP-WXT trigger 01709200707 is likely a flaring star
  70. GRB 250823A: COLIBRÍ optical observations
  71. The EP-WXT trigger 01709200706 is likely a flaring star
  72. GRB 250823A: SVOM/VT optical observation
  73. GRB 250824A: Fermi GBM Final Real-time Localization
  74. GRB 250823A: Swift/UVOT Detection
  75. GRB 250823A: NOT optical observations
  76. LIGO/Virgo/KAGRA S250818k: CFH/MegaCam follow-up observation for AT2025ulz
  77. LIGO/Virgo/KAGRA S250818k: COLIBRÍ confirmation of rebrightening of AT2025ulz
  78. GRB 250823A: Fermi GBM Observation
  79. GRB 250818B: MeerKAT Detection
  80. GRB 250823A: Enhanced Swift-XRT position
  81. GRB 250823A: LCOGT Optical Detection
  82. GRB 250823A: BOOTES6/DPRT early optical detection
  83. GRB 250823A: Liverpool Telescope optical detection
  84. GRB 250823A: Swift detection of a burst
  85. GRB 250823A: Fermi GBM Final Real-time Localization
  86. Swift GRB250823.84: Global MASTER-Net observations report
  87. Konus-Wind detection of GRB 250821B
  88. LIGO/Virgo/KAGRA S250818k: Rebrightening detected with Gemini/GMOS
  89. LIGO/Virgo/KAGRA S250818k: HST nIR detection of AT 2025ulz
  90. LIGO/Virgo/KAGRA S250818k: J-GEM follow-up observation for AT2025ulz
  91. LIGO/Virgo/KAGRA S250818k: PRIME nIR observations of AT2025ulz
  92. LIGO/Virgo/KAGRA S250818k: JinShan optical observations of AT2025ulz
  93. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Optical Detection of AT2025ulz
  94. LIGO/Virgo/Kagra S250818k: STEP/T80N upper limits on 2025ulz
  95. LIGO/Virgo/KAGRA S250818k: 3 GHz MeerKAT observations of AT2025ulz
  96. GRB 250806A: Gemini observations of host galaxy candidate
  97. IPN triangulation of GRB 250821B (long/bright)
  98. GRB 250821A: Kilonova-Catcher optical upper limits
  99. EP250821a: Swift/XRT counterpart fading
  100. GRB 250812A: SVOM/ECLAIRs refined analysis

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