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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 S250830bp GLADEnet Completeness: Potential Host Galaxies in the 90% Credible Volume
  2. LIGO/Virgo/KAGRA S250830bp: NED Galaxies in the 4-Update Localization Volume
  3. LIGO/Virgo/KAGRA S250830bp: Updated Sky localization, EM Bright Classification, and Source Classification
  4. LIGO/Virgo/KAGRA S250830bp: Identification of a GW compact binary merger candidate
  5. EP-WXT trigger 01709200994: Liverpool Telescope upper limits
  6. GRB 250830B: Swift ToO observations
  7. EP-WXT trigger 01709200994: confirmation of a stellar flare by BOOTES-6
  8. GRB 250830B: MAXI/GSC detection
  9. LIGO/Virgo/KAGRA S250830m: Identification of a GW compact binary merger candidate
  10. GRB 250830A / MAXI J0853+337: MAXI/GSC detection
  11. The EP-WXT trigger 01709200994 is likely a flaring star
  12. GRB 250828B: Swift-BAT refined analysis
  13. EP250821a: SOAR observations
  14. EP250827a: very early ATLAS detections, starting 43 sec after the EP trigger
  15. LIGO/Virgo/KAGRA S250725j: Observations with the NSF-DOE Vera C. Rubin Observatory
  16. LIGO/Virgo/KAGRA S250818k: MeerKAT detection of an increase in radio flux from AT2025ulz
  17. GRB 250808B: SVOM detection of a burst through offline search
  18. EP250828a: refined analysis of the EP-WXT and EP-FXT observations
  19. EP250828a: Optical counterpart detection with Kinder observations
  20. EP250828a: Liverpool Telescope upper limits
  21. Swift GRB 250828B: Global MASTER-Net observations report
  22. EP250828a: Global MASTER-Net observations report
  23. EP-WXT trigger 01709200800 : KAIT optical observations
  24. EP250828a: KAIT optical upper limit
  25. EP250827a: Swift/UVOT Detection
  26. EP250828a: NOT optical counterpart confirmation
  27. EP250828a: SVOM/VT optical candidate
  28. EP250828a: Seimei/TriCCS optical counterpart detection
  29. GRB 250828B: Swift detection of a burst
  30. EP250827a: STEP/T80S Confirmation of fading optical counterpart
  31. EP250828a: Optical upper limit with Kinder observations
  32. LIGO/Virgo/KAGRA S250827fo: Updated Sky localization
  33. LIGO/Virgo/KAGRA S250818k: uGMRT 1.3 GHz observations of AT2025ulz
  34. EP250827a: LCO observations show fading optical counterpart
  35. GRB 250828A: Fermi GBM Final Localization
  36. EP250828a: Einstein Probe detection of an X-ray transient
  37. EP250827a: Preliminary analysis of the EP-WXT and EP-FXT observations
  38. GRID detection of GRB 250824A
  39. LIGO/Virgo/KAGRA S250827fo: Identification of a GW compact binary merger candidate
  40. EP250827A: VLT/X-shooter redshift confirmation
  41. Fermi GRB 250827A: Global MASTER-Net observations report
  42. EP250827a: confirmation of optical rebrightening with LCO
  43. EP250827a: GOTO observation of the optical afterglow
  44. GRB 250826A: SVOM/GRM observation
  45. GRB 250827A: Fermi GBM Final Real-time Localization
  46. EP250827A: An optical rebrightening was detected by LCO.
  47. EP250827a: Swift-XRT counterpart detection
  48. LIGO/Virgo/KAGRA S250827l: Updated Sky localization
  49. The EP-WXT trigger 01709200800 is likely a flaring star
  50. EP250827a: TRT optical observations
  51. EP250827a: BOOTES-7 early optical dectection
  52. EP250827a / GRB 250827A: MASTER-OAFA OT observation
  53. EP250827a: Gemini-South redshift z = 1.613
  54. EP250827a: Global MASTER-Net observations report
  55. EP250827a: Las Cumbres independent detection of the optical counterpart
  56. EP250827a: Gemini-South optical counterpart detection
  57. EP250827a: Einstein Probe detection of an X-ray transient
  58. LIGO/Virgo/KAGRA S250827l: Identification of a GW compact binary merger candidate
  59. Fermi GRB 250826A: Global MASTER-Net observations report
  60. GRB 250806A: HiPERCAM/GTC limits on a possible supernova
  61. EP250821a: Gemini GMOS Redshift Confirmation
  62. LIGO/Virgo/KAGRA S250818k: SAO RAS BTA z-band observations of AT2025ulz
  63. Fermi trigger No 777883624: Global MASTER-Net observations report
  64. Fermi Gamma-ray Burst Monitor trigger 777883624/250826283 is not a GRB
  65. GRB 250826A: Fermi GBM Final Real-time Localization
  66. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Confirmation of Rebrightening of AT2025ulz
  67. Fermi GRB 250824B: Global MASTER-Net observations report
  68. LIGO/Virgo/KAGRA S250818k: VLA upper limits on AT2025ulz
  69. LIGO/Virgo/KAGRA S250818k: nature of the AT2025ulz/ZTF25abjmnnps OT
  70. LIGO/Virgo/KAGRA S250818k: Pan-STARRS imaging confirms re-brightening of SN2025ulz
  71. GRB 250823A: Swift-BAT refined analysis
  72. LIGO/Virgo/KAGRA S250818k: Continued Keck I LRIS spectroscopy of ZTF25abjmnps (AT2025ulz)
  73. GRB 250821B: AstroSat CZTI detection
  74. GRB 250819A: AstroSat CZTI detection
  75. LIGO/Virgo/KAGRA S250818k: FTW Observations Show Continued Reddening of AT 2025ulz
  76. LIGO/Virgo/KAGRA S250818k: MASTER predicovery limits of the AT2025ulz/ZTF25abjmnps KN candidate
  77. GRB 250821B: Insight-HXMT detection
  78. LIGO/Virgo/KAGRA S250818k: ENGRAVE observations of SN 2025ulz as a type II supernova
  79. GRB 250823A: Swift-XRT refined Analysis
  80. EP250821a: MeerKAT radio counterpart
  81. EP triggers 01709200706 and 01709200707: GOTO confirmation of flaring stars
  82. LIGO/Virgo/KAGRA S250818k: Swift Observations of AT 2025ulz - Second Epoch
  83. GRB 250824B: Fermi GBM Final Real-time Localization
  84. The EP-WXT trigger 01709200707 is likely a flaring star
  85. GRB 250823A: COLIBRÍ optical observations
  86. The EP-WXT trigger 01709200706 is likely a flaring star
  87. GRB 250823A: SVOM/VT optical observation
  88. GRB 250824A: Fermi GBM Final Real-time Localization
  89. GRB 250823A: Swift/UVOT Detection
  90. GRB 250823A: NOT optical observations
  91. LIGO/Virgo/KAGRA S250818k: CFH/MegaCam follow-up observation for AT2025ulz
  92. LIGO/Virgo/KAGRA S250818k: COLIBRÍ confirmation of rebrightening of AT2025ulz
  93. GRB 250823A: Fermi GBM Observation
  94. GRB 250818B: MeerKAT Detection
  95. GRB 250823A: Enhanced Swift-XRT position
  96. GRB 250823A: LCOGT Optical Detection
  97. GRB 250823A: BOOTES6/DPRT early optical detection
  98. GRB 250823A: Liverpool Telescope optical detection
  99. GRB 250823A: Swift detection of a burst
  100. GRB 250823A: Fermi GBM Final Real-time Localization

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