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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. EP250830a/GRB 250830B: Einstein Probe detection of an X-ray transient and Swift/XRT follow-up
  2. LIGO/Virgo/KAGRA S250830bp: Coverage and upper limits from MAXI/GSC observations
  3. LIGO/Virgo/KAGRA S250830bp GLADEnet Completeness: Potential Host Galaxies in the 90% Credible Volume
  4. LIGO/Virgo/KAGRA S250830bp: NED Galaxies in the 4-Update Localization Volume
  5. LIGO/Virgo/KAGRA S250830bp: Updated Sky localization, EM Bright Classification, and Source Classification
  6. LIGO/Virgo/KAGRA S250830bp: Identification of a GW compact binary merger candidate
  7. EP-WXT trigger 01709200994: Liverpool Telescope upper limits
  8. GRB 250830B: Swift ToO observations
  9. EP-WXT trigger 01709200994: confirmation of a stellar flare by BOOTES-6
  10. GRB 250830B: MAXI/GSC detection
  11. LIGO/Virgo/KAGRA S250830m: Identification of a GW compact binary merger candidate
  12. GRB 250830A / MAXI J0853+337: MAXI/GSC detection
  13. The EP-WXT trigger 01709200994 is likely a flaring star
  14. GRB 250828B: Swift-BAT refined analysis
  15. EP250821a: SOAR observations
  16. EP250827a: very early ATLAS detections, starting 43 sec after the EP trigger
  17. LIGO/Virgo/KAGRA S250725j: Observations with the NSF-DOE Vera C. Rubin Observatory
  18. LIGO/Virgo/KAGRA S250818k: MeerKAT detection of an increase in radio flux from AT2025ulz
  19. GRB 250808B: SVOM detection of a burst through offline search
  20. EP250828a: refined analysis of the EP-WXT and EP-FXT observations
  21. EP250828a: Optical counterpart detection with Kinder observations
  22. EP250828a: Liverpool Telescope upper limits
  23. Swift GRB 250828B: Global MASTER-Net observations report
  24. EP250828a: Global MASTER-Net observations report
  25. EP-WXT trigger 01709200800 : KAIT optical observations
  26. EP250828a: KAIT optical upper limit
  27. EP250827a: Swift/UVOT Detection
  28. EP250828a: NOT optical counterpart confirmation
  29. EP250828a: SVOM/VT optical candidate
  30. EP250828a: Seimei/TriCCS optical counterpart detection
  31. GRB 250828B: Swift detection of a burst
  32. EP250827a: STEP/T80S Confirmation of fading optical counterpart
  33. EP250828a: Optical upper limit with Kinder observations
  34. LIGO/Virgo/KAGRA S250827fo: Updated Sky localization
  35. LIGO/Virgo/KAGRA S250818k: uGMRT 1.3 GHz observations of AT2025ulz
  36. EP250827a: LCO observations show fading optical counterpart
  37. GRB 250828A: Fermi GBM Final Localization
  38. EP250828a: Einstein Probe detection of an X-ray transient
  39. EP250827a: Preliminary analysis of the EP-WXT and EP-FXT observations
  40. GRID detection of GRB 250824A
  41. LIGO/Virgo/KAGRA S250827fo: Identification of a GW compact binary merger candidate
  42. EP250827A: VLT/X-shooter redshift confirmation
  43. Fermi GRB 250827A: Global MASTER-Net observations report
  44. EP250827a: confirmation of optical rebrightening with LCO
  45. EP250827a: GOTO observation of the optical afterglow
  46. GRB 250826A: SVOM/GRM observation
  47. GRB 250827A: Fermi GBM Final Real-time Localization
  48. EP250827A: An optical rebrightening was detected by LCO.
  49. EP250827a: Swift-XRT counterpart detection
  50. LIGO/Virgo/KAGRA S250827l: Updated Sky localization
  51. The EP-WXT trigger 01709200800 is likely a flaring star
  52. EP250827a: TRT optical observations
  53. EP250827a: BOOTES-7 early optical dectection
  54. EP250827a / GRB 250827A: MASTER-OAFA OT observation
  55. EP250827a: Gemini-South redshift z = 1.613
  56. EP250827a: Global MASTER-Net observations report
  57. EP250827a: Las Cumbres independent detection of the optical counterpart
  58. EP250827a: Gemini-South optical counterpart detection
  59. EP250827a: Einstein Probe detection of an X-ray transient
  60. LIGO/Virgo/KAGRA S250827l: Identification of a GW compact binary merger candidate
  61. Fermi GRB 250826A: Global MASTER-Net observations report
  62. GRB 250806A: HiPERCAM/GTC limits on a possible supernova
  63. EP250821a: Gemini GMOS Redshift Confirmation
  64. LIGO/Virgo/KAGRA S250818k: SAO RAS BTA z-band observations of AT2025ulz
  65. Fermi trigger No 777883624: Global MASTER-Net observations report
  66. Fermi Gamma-ray Burst Monitor trigger 777883624/250826283 is not a GRB
  67. GRB 250826A: Fermi GBM Final Real-time Localization
  68. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Confirmation of Rebrightening of AT2025ulz
  69. Fermi GRB 250824B: Global MASTER-Net observations report
  70. LIGO/Virgo/KAGRA S250818k: VLA upper limits on AT2025ulz
  71. LIGO/Virgo/KAGRA S250818k: nature of the AT2025ulz/ZTF25abjmnnps OT
  72. LIGO/Virgo/KAGRA S250818k: Pan-STARRS imaging confirms re-brightening of SN2025ulz
  73. GRB 250823A: Swift-BAT refined analysis
  74. LIGO/Virgo/KAGRA S250818k: Continued Keck I LRIS spectroscopy of ZTF25abjmnps (AT2025ulz)
  75. GRB 250821B: AstroSat CZTI detection
  76. GRB 250819A: AstroSat CZTI detection
  77. LIGO/Virgo/KAGRA S250818k: FTW Observations Show Continued Reddening of AT 2025ulz
  78. LIGO/Virgo/KAGRA S250818k: MASTER predicovery limits of the AT2025ulz/ZTF25abjmnps KN candidate
  79. GRB 250821B: Insight-HXMT detection
  80. LIGO/Virgo/KAGRA S250818k: ENGRAVE observations of SN 2025ulz as a type II supernova
  81. GRB 250823A: Swift-XRT refined Analysis
  82. EP250821a: MeerKAT radio counterpart
  83. EP triggers 01709200706 and 01709200707: GOTO confirmation of flaring stars
  84. LIGO/Virgo/KAGRA S250818k: Swift Observations of AT 2025ulz - Second Epoch
  85. GRB 250824B: Fermi GBM Final Real-time Localization
  86. The EP-WXT trigger 01709200707 is likely a flaring star
  87. GRB 250823A: COLIBRÍ optical observations
  88. The EP-WXT trigger 01709200706 is likely a flaring star
  89. GRB 250823A: SVOM/VT optical observation
  90. GRB 250824A: Fermi GBM Final Real-time Localization
  91. GRB 250823A: Swift/UVOT Detection
  92. GRB 250823A: NOT optical observations
  93. LIGO/Virgo/KAGRA S250818k: CFH/MegaCam follow-up observation for AT2025ulz
  94. LIGO/Virgo/KAGRA S250818k: COLIBRÍ confirmation of rebrightening of AT2025ulz
  95. GRB 250823A: Fermi GBM Observation
  96. GRB 250818B: MeerKAT Detection
  97. GRB 250823A: Enhanced Swift-XRT position
  98. GRB 250823A: LCOGT Optical Detection
  99. GRB 250823A: BOOTES6/DPRT early optical detection
  100. GRB 250823A: Liverpool Telescope optical detection

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