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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. Swift GRB 250828B: Global MASTER-Net observations report
  2. EP250828a: Global MASTER-Net observations report
  3. EP-WXT trigger 01709200800 : KAIT optical observations
  4. EP250828a: KAIT optical upper limit
  5. EP250827a: Swift/UVOT Detection
  6. EP250828a: NOT optical counterpart confirmation
  7. EP250828a: SVOM/VT optical candidate
  8. EP250828a: Seimei/TriCCS optical counterpart detection
  9. GRB 250828B: Swift detection of a burst
  10. EP250827a: STEP/T80S Confirmation of fading optical counterpart
  11. EP250828a: Optical upper limit with Kinder observations
  12. LIGO/Virgo/KAGRA S250827fo: Updated Sky localization
  13. LIGO/Virgo/KAGRA S250818k: uGMRT 1.3 GHz observations of AT2025ulz
  14. EP250827a: LCO observations show fading optical counterpart
  15. GRB 250828A: Fermi GBM Final Localization
  16. EP250828a: Einstein Probe detection of an X-ray transient
  17. EP250827a: Preliminary analysis of the EP-WXT and EP-FXT observations
  18. GRID detection of GRB 250824A
  19. LIGO/Virgo/KAGRA S250827fo: Identification of a GW compact binary merger candidate
  20. EP250827A: VLT/X-shooter redshift confirmation
  21. Fermi GRB 250827A: Global MASTER-Net observations report
  22. EP250827a: confirmation of optical rebrightening with LCO
  23. EP250827a: GOTO observation of the optical afterglow
  24. GRB 250826A: SVOM/GRM observation
  25. GRB 250827A: Fermi GBM Final Real-time Localization
  26. EP250827A: An optical rebrightening was detected by LCO.
  27. EP250827a: Swift-XRT counterpart detection
  28. LIGO/Virgo/KAGRA S250827l: Updated Sky localization
  29. The EP-WXT trigger 01709200800 is likely a flaring star
  30. EP250827a: TRT optical observations
  31. EP250827a: BOOTES-7 early optical dectection
  32. EP250827a / GRB 250827A: MASTER-OAFA OT observation
  33. EP250827a: Gemini-South redshift z = 1.613
  34. EP250827a: Global MASTER-Net observations report
  35. EP250827a: Las Cumbres independent detection of the optical counterpart
  36. EP250827a: Gemini-South optical counterpart detection
  37. EP250827a: Einstein Probe detection of an X-ray transient
  38. LIGO/Virgo/KAGRA S250827l: Identification of a GW compact binary merger candidate
  39. Fermi GRB 250826A: Global MASTER-Net observations report
  40. GRB 250806A: HiPERCAM/GTC limits on a possible supernova
  41. EP250821a: Gemini GMOS Redshift Confirmation
  42. LIGO/Virgo/KAGRA S250818k: SAO RAS BTA z-band observations of AT2025ulz
  43. Fermi trigger No 777883624: Global MASTER-Net observations report
  44. Fermi Gamma-ray Burst Monitor trigger 777883624/250826283 is not a GRB
  45. GRB 250826A: Fermi GBM Final Real-time Localization
  46. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Confirmation of Rebrightening of AT2025ulz
  47. Fermi GRB 250824B: Global MASTER-Net observations report
  48. LIGO/Virgo/KAGRA S250818k: VLA upper limits on AT2025ulz
  49. LIGO/Virgo/KAGRA S250818k: nature of the AT2025ulz/ZTF25abjmnnps OT
  50. LIGO/Virgo/KAGRA S250818k: Pan-STARRS imaging confirms re-brightening of SN2025ulz
  51. GRB 250823A: Swift-BAT refined analysis
  52. LIGO/Virgo/KAGRA S250818k: Continued Keck I LRIS spectroscopy of ZTF25abjmnps (AT2025ulz)
  53. GRB 250821B: AstroSat CZTI detection
  54. GRB 250819A: AstroSat CZTI detection
  55. LIGO/Virgo/KAGRA S250818k: FTW Observations Show Continued Reddening of AT 2025ulz
  56. LIGO/Virgo/KAGRA S250818k: MASTER predicovery limits of the AT2025ulz/ZTF25abjmnps KN candidate
  57. GRB 250821B: Insight-HXMT detection
  58. LIGO/Virgo/KAGRA S250818k: ENGRAVE observations of SN 2025ulz as a type II supernova
  59. GRB 250823A: Swift-XRT refined Analysis
  60. EP250821a: MeerKAT radio counterpart
  61. EP triggers 01709200706 and 01709200707: GOTO confirmation of flaring stars
  62. LIGO/Virgo/KAGRA S250818k: Swift Observations of AT 2025ulz - Second Epoch
  63. GRB 250824B: Fermi GBM Final Real-time Localization
  64. The EP-WXT trigger 01709200707 is likely a flaring star
  65. GRB 250823A: COLIBRÍ optical observations
  66. The EP-WXT trigger 01709200706 is likely a flaring star
  67. GRB 250823A: SVOM/VT optical observation
  68. GRB 250824A: Fermi GBM Final Real-time Localization
  69. GRB 250823A: Swift/UVOT Detection
  70. GRB 250823A: NOT optical observations
  71. LIGO/Virgo/KAGRA S250818k: CFH/MegaCam follow-up observation for AT2025ulz
  72. LIGO/Virgo/KAGRA S250818k: COLIBRÍ confirmation of rebrightening of AT2025ulz
  73. GRB 250823A: Fermi GBM Observation
  74. GRB 250818B: MeerKAT Detection
  75. GRB 250823A: Enhanced Swift-XRT position
  76. GRB 250823A: LCOGT Optical Detection
  77. GRB 250823A: BOOTES6/DPRT early optical detection
  78. GRB 250823A: Liverpool Telescope optical detection
  79. GRB 250823A: Swift detection of a burst
  80. GRB 250823A: Fermi GBM Final Real-time Localization
  81. Swift GRB250823.84: Global MASTER-Net observations report
  82. Konus-Wind detection of GRB 250821B
  83. LIGO/Virgo/KAGRA S250818k: Rebrightening detected with Gemini/GMOS
  84. LIGO/Virgo/KAGRA S250818k: HST nIR detection of AT 2025ulz
  85. LIGO/Virgo/KAGRA S250818k: J-GEM follow-up observation for AT2025ulz
  86. LIGO/Virgo/KAGRA S250818k: PRIME nIR observations of AT2025ulz
  87. LIGO/Virgo/KAGRA S250818k: JinShan optical observations of AT2025ulz
  88. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Optical Detection of AT2025ulz
  89. LIGO/Virgo/Kagra S250818k: STEP/T80N upper limits on 2025ulz
  90. LIGO/Virgo/KAGRA S250818k: 3 GHz MeerKAT observations of AT2025ulz
  91. GRB 250806A: Gemini observations of host galaxy candidate
  92. IPN triangulation of GRB 250821B (long/bright)
  93. GRB 250821A: Kilonova-Catcher optical upper limits
  94. EP250821a: Swift/XRT counterpart fading
  95. GRB 250812A: SVOM/ECLAIRs refined analysis
  96. GRB 250821A: Swift-BAT refined analysis
  97. LIGO/Virgo/KAGRA S250818k: Pan-STARRS coverage of the skymap and candidate counterparts
  98. LIGO/Virgo/KAGRA S250818k: NOT optical observations of AT2025ulz
  99. EP250821a: Swift/UVOT further observations.
  100. EP250821a: VLT X-shooter spectroscopic redshift z = 0.577

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