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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 S250830m: Identification of a GW compact binary merger candidate
  2. GRB 250830A / MAXI J0853+337: MAXI/GSC detection
  3. The EP-WXT trigger 01709200994 is likely a flaring star
  4. GRB 250828B: Swift-BAT refined analysis
  5. EP250821a: SOAR observations
  6. EP250827a: very early ATLAS detections, starting 43 sec after the EP trigger
  7. LIGO/Virgo/KAGRA S250725j: Observations with the NSF-DOE Vera C. Rubin Observatory
  8. LIGO/Virgo/KAGRA S250818k: MeerKAT detection of an increase in radio flux from AT2025ulz
  9. GRB 250808B: SVOM detection of a burst through offline search
  10. EP250828a: refined analysis of the EP-WXT and EP-FXT observations
  11. EP250828a: Optical counterpart detection with Kinder observations
  12. EP250828a: Liverpool Telescope upper limits
  13. Swift GRB 250828B: Global MASTER-Net observations report
  14. EP250828a: Global MASTER-Net observations report
  15. EP-WXT trigger 01709200800 : KAIT optical observations
  16. EP250828a: KAIT optical upper limit
  17. EP250827a: Swift/UVOT Detection
  18. EP250828a: NOT optical counterpart confirmation
  19. EP250828a: SVOM/VT optical candidate
  20. EP250828a: Seimei/TriCCS optical counterpart detection
  21. GRB 250828B: Swift detection of a burst
  22. EP250827a: STEP/T80S Confirmation of fading optical counterpart
  23. EP250828a: Optical upper limit with Kinder observations
  24. LIGO/Virgo/KAGRA S250827fo: Updated Sky localization
  25. LIGO/Virgo/KAGRA S250818k: uGMRT 1.3 GHz observations of AT2025ulz
  26. EP250827a: LCO observations show fading optical counterpart
  27. GRB 250828A: Fermi GBM Final Localization
  28. EP250828a: Einstein Probe detection of an X-ray transient
  29. EP250827a: Preliminary analysis of the EP-WXT and EP-FXT observations
  30. GRID detection of GRB 250824A
  31. LIGO/Virgo/KAGRA S250827fo: Identification of a GW compact binary merger candidate
  32. EP250827A: VLT/X-shooter redshift confirmation
  33. Fermi GRB 250827A: Global MASTER-Net observations report
  34. EP250827a: confirmation of optical rebrightening with LCO
  35. EP250827a: GOTO observation of the optical afterglow
  36. GRB 250826A: SVOM/GRM observation
  37. GRB 250827A: Fermi GBM Final Real-time Localization
  38. EP250827A: An optical rebrightening was detected by LCO.
  39. EP250827a: Swift-XRT counterpart detection
  40. LIGO/Virgo/KAGRA S250827l: Updated Sky localization
  41. The EP-WXT trigger 01709200800 is likely a flaring star
  42. EP250827a: TRT optical observations
  43. EP250827a: BOOTES-7 early optical dectection
  44. EP250827a / GRB 250827A: MASTER-OAFA OT observation
  45. EP250827a: Gemini-South redshift z = 1.613
  46. EP250827a: Global MASTER-Net observations report
  47. EP250827a: Las Cumbres independent detection of the optical counterpart
  48. EP250827a: Gemini-South optical counterpart detection
  49. EP250827a: Einstein Probe detection of an X-ray transient
  50. LIGO/Virgo/KAGRA S250827l: Identification of a GW compact binary merger candidate
  51. Fermi GRB 250826A: Global MASTER-Net observations report
  52. GRB 250806A: HiPERCAM/GTC limits on a possible supernova
  53. EP250821a: Gemini GMOS Redshift Confirmation
  54. LIGO/Virgo/KAGRA S250818k: SAO RAS BTA z-band observations of AT2025ulz
  55. Fermi trigger No 777883624: Global MASTER-Net observations report
  56. Fermi Gamma-ray Burst Monitor trigger 777883624/250826283 is not a GRB
  57. GRB 250826A: Fermi GBM Final Real-time Localization
  58. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Confirmation of Rebrightening of AT2025ulz
  59. Fermi GRB 250824B: Global MASTER-Net observations report
  60. LIGO/Virgo/KAGRA S250818k: VLA upper limits on AT2025ulz
  61. LIGO/Virgo/KAGRA S250818k: nature of the AT2025ulz/ZTF25abjmnnps OT
  62. LIGO/Virgo/KAGRA S250818k: Pan-STARRS imaging confirms re-brightening of SN2025ulz
  63. GRB 250823A: Swift-BAT refined analysis
  64. LIGO/Virgo/KAGRA S250818k: Continued Keck I LRIS spectroscopy of ZTF25abjmnps (AT2025ulz)
  65. GRB 250821B: AstroSat CZTI detection
  66. GRB 250819A: AstroSat CZTI detection
  67. LIGO/Virgo/KAGRA S250818k: FTW Observations Show Continued Reddening of AT 2025ulz
  68. LIGO/Virgo/KAGRA S250818k: MASTER predicovery limits of the AT2025ulz/ZTF25abjmnps KN candidate
  69. GRB 250821B: Insight-HXMT detection
  70. LIGO/Virgo/KAGRA S250818k: ENGRAVE observations of SN 2025ulz as a type II supernova
  71. GRB 250823A: Swift-XRT refined Analysis
  72. EP250821a: MeerKAT radio counterpart
  73. EP triggers 01709200706 and 01709200707: GOTO confirmation of flaring stars
  74. LIGO/Virgo/KAGRA S250818k: Swift Observations of AT 2025ulz - Second Epoch
  75. GRB 250824B: Fermi GBM Final Real-time Localization
  76. The EP-WXT trigger 01709200707 is likely a flaring star
  77. GRB 250823A: COLIBRÍ optical observations
  78. The EP-WXT trigger 01709200706 is likely a flaring star
  79. GRB 250823A: SVOM/VT optical observation
  80. GRB 250824A: Fermi GBM Final Real-time Localization
  81. GRB 250823A: Swift/UVOT Detection
  82. GRB 250823A: NOT optical observations
  83. LIGO/Virgo/KAGRA S250818k: CFH/MegaCam follow-up observation for AT2025ulz
  84. LIGO/Virgo/KAGRA S250818k: COLIBRÍ confirmation of rebrightening of AT2025ulz
  85. GRB 250823A: Fermi GBM Observation
  86. GRB 250818B: MeerKAT Detection
  87. GRB 250823A: Enhanced Swift-XRT position
  88. GRB 250823A: LCOGT Optical Detection
  89. GRB 250823A: BOOTES6/DPRT early optical detection
  90. GRB 250823A: Liverpool Telescope optical detection
  91. GRB 250823A: Swift detection of a burst
  92. GRB 250823A: Fermi GBM Final Real-time Localization
  93. Swift GRB250823.84: Global MASTER-Net observations report
  94. Konus-Wind detection of GRB 250821B
  95. LIGO/Virgo/KAGRA S250818k: Rebrightening detected with Gemini/GMOS
  96. LIGO/Virgo/KAGRA S250818k: HST nIR detection of AT 2025ulz
  97. LIGO/Virgo/KAGRA S250818k: J-GEM follow-up observation for AT2025ulz
  98. LIGO/Virgo/KAGRA S250818k: PRIME nIR observations of AT2025ulz
  99. LIGO/Virgo/KAGRA S250818k: JinShan optical observations of AT2025ulz
  100. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Optical Detection of AT2025ulz

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