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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: uGMRT 1.3 GHz observations of AT2025ulz
  2. EP250827a: LCO observations show fading optical counterpart
  3. GRB 250828A: Fermi GBM Final Localization
  4. EP250828a: Einstein Probe detection of an X-ray transient
  5. EP250827a: Preliminary analysis of the EP-WXT and EP-FXT observations
  6. GRID detection of GRB 250824A
  7. LIGO/Virgo/KAGRA S250827fo: Identification of a GW compact binary merger candidate
  8. EP250827A: VLT/X-shooter redshift confirmation
  9. Fermi GRB 250827A: Global MASTER-Net observations report
  10. EP250827a: confirmation of optical rebrightening with LCO
  11. EP250827a: GOTO observation of the optical afterglow
  12. GRB 250826A: SVOM/GRM observation
  13. GRB 250827A: Fermi GBM Final Real-time Localization
  14. EP250827A: An optical rebrightening was detected by LCO.
  15. EP250827a: Swift-XRT counterpart detection
  16. LIGO/Virgo/KAGRA S250827l: Updated Sky localization
  17. The EP-WXT trigger 01709200800 is likely a flaring star
  18. EP250827a: TRT optical observations
  19. EP250827a: BOOTES-7 early optical dectection
  20. EP250827a / GRB 250827A: MASTER-OAFA OT observation
  21. EP250827a: Gemini-South redshift z = 1.613
  22. EP250827a: Global MASTER-Net observations report
  23. EP250827a: Las Cumbres independent detection of the optical counterpart
  24. EP250827a: Gemini-South optical counterpart detection
  25. EP250827a: Einstein Probe detection of an X-ray transient
  26. LIGO/Virgo/KAGRA S250827l: Identification of a GW compact binary merger candidate
  27. Fermi GRB 250826A: Global MASTER-Net observations report
  28. GRB 250806A: HiPERCAM/GTC limits on a possible supernova
  29. EP250821a: Gemini GMOS Redshift Confirmation
  30. LIGO/Virgo/KAGRA S250818k: SAO RAS BTA z-band observations of AT2025ulz
  31. Fermi trigger No 777883624: Global MASTER-Net observations report
  32. Fermi Gamma-ray Burst Monitor trigger 777883624/250826283 is not a GRB
  33. GRB 250826A: Fermi GBM Final Real-time Localization
  34. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Confirmation of Rebrightening of AT2025ulz
  35. Fermi GRB 250824B: Global MASTER-Net observations report
  36. LIGO/Virgo/KAGRA S250818k: VLA upper limits on AT2025ulz
  37. LIGO/Virgo/KAGRA S250818k: nature of the AT2025ulz/ZTF25abjmnnps OT
  38. LIGO/Virgo/KAGRA S250818k: Pan-STARRS imaging confirms re-brightening of SN2025ulz
  39. GRB 250823A: Swift-BAT refined analysis
  40. LIGO/Virgo/KAGRA S250818k: Continued Keck I LRIS spectroscopy of ZTF25abjmnps (AT2025ulz)
  41. GRB 250821B: AstroSat CZTI detection
  42. GRB 250819A: AstroSat CZTI detection
  43. LIGO/Virgo/KAGRA S250818k: FTW Observations Show Continued Reddening of AT 2025ulz
  44. LIGO/Virgo/KAGRA S250818k: MASTER predicovery limits of the AT2025ulz/ZTF25abjmnps KN candidate
  45. GRB 250821B: Insight-HXMT detection
  46. LIGO/Virgo/KAGRA S250818k: ENGRAVE observations of SN 2025ulz as a type II supernova
  47. GRB 250823A: Swift-XRT refined Analysis
  48. EP250821a: MeerKAT radio counterpart
  49. EP triggers 01709200706 and 01709200707: GOTO confirmation of flaring stars
  50. LIGO/Virgo/KAGRA S250818k: Swift Observations of AT 2025ulz - Second Epoch
  51. GRB 250824B: Fermi GBM Final Real-time Localization
  52. The EP-WXT trigger 01709200707 is likely a flaring star
  53. GRB 250823A: COLIBRÍ optical observations
  54. The EP-WXT trigger 01709200706 is likely a flaring star
  55. GRB 250823A: SVOM/VT optical observation
  56. GRB 250824A: Fermi GBM Final Real-time Localization
  57. GRB 250823A: Swift/UVOT Detection
  58. GRB 250823A: NOT optical observations
  59. LIGO/Virgo/KAGRA S250818k: CFH/MegaCam follow-up observation for AT2025ulz
  60. LIGO/Virgo/KAGRA S250818k: COLIBRÍ confirmation of rebrightening of AT2025ulz
  61. GRB 250823A: Fermi GBM Observation
  62. GRB 250818B: MeerKAT Detection
  63. GRB 250823A: Enhanced Swift-XRT position
  64. GRB 250823A: LCOGT Optical Detection
  65. GRB 250823A: BOOTES6/DPRT early optical detection
  66. GRB 250823A: Liverpool Telescope optical detection
  67. GRB 250823A: Swift detection of a burst
  68. GRB 250823A: Fermi GBM Final Real-time Localization
  69. Swift GRB250823.84: Global MASTER-Net observations report
  70. Konus-Wind detection of GRB 250821B
  71. LIGO/Virgo/KAGRA S250818k: Rebrightening detected with Gemini/GMOS
  72. LIGO/Virgo/KAGRA S250818k: HST nIR detection of AT 2025ulz
  73. LIGO/Virgo/KAGRA S250818k: J-GEM follow-up observation for AT2025ulz
  74. LIGO/Virgo/KAGRA S250818k: PRIME nIR observations of AT2025ulz
  75. LIGO/Virgo/KAGRA S250818k: JinShan optical observations of AT2025ulz
  76. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Optical Detection of AT2025ulz
  77. LIGO/Virgo/Kagra S250818k: STEP/T80N upper limits on 2025ulz
  78. LIGO/Virgo/KAGRA S250818k: 3 GHz MeerKAT observations of AT2025ulz
  79. GRB 250806A: Gemini observations of host galaxy candidate
  80. IPN triangulation of GRB 250821B (long/bright)
  81. GRB 250821A: Kilonova-Catcher optical upper limits
  82. EP250821a: Swift/XRT counterpart fading
  83. GRB 250812A: SVOM/ECLAIRs refined analysis
  84. GRB 250821A: Swift-BAT refined analysis
  85. LIGO/Virgo/KAGRA S250818k: Pan-STARRS coverage of the skymap and candidate counterparts
  86. LIGO/Virgo/KAGRA S250818k: NOT optical observations of AT2025ulz
  87. EP250821a: Swift/UVOT further observations.
  88. EP250821a: VLT X-shooter spectroscopic redshift z = 0.577
  89. LIGO/Virgo/KAGRA S250818k: GRAWITA TNG NIR observations of AT2025ulz
  90. GRB 250821A: VLT/FORS2 Optical Observation
  91. GRB 250821A: GECAM-B detection
  92. GRB 250821B: SVOM/GRM observation
  93. EP250821a: SVOM/VT optical observation
  94. Fermi GRB 250821B: Global MASTER-Net observations report
  95. GRB 250821A: NOT z-band upper limit
  96. GRB 250821C: Fermi GBM Final Real-time Localization
  97. GRB 250821A: KAIT optical upper limit
  98. LIGO/Virgo/KAGRA S250818k: Continued fading and reddening of AT2025ulz from Keck/LRIS imaging observations
  99. GRB 250821A: Swift-XRT refined Analysis
  100. Swift GRB 250821A: Global MASTER-Net observations report

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