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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. GRB 250831A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  2. GRB 250831A: SVOM/VT upper limit with VHF data
  3. GRB 250831A: SVOM detection of a soft burst
  4. GRB 250830B: Swift-XRT observations
  5. EP250830a: Global MASTER-Net observations report
  6. EP250830a/GRB 250830B: Einstein Probe detection of an X-ray transient and Swift/XRT follow-up
  7. LIGO/Virgo/KAGRA S250830bp: Coverage and upper limits from MAXI/GSC observations
  8. LIGO/Virgo/KAGRA S250830bp GLADEnet Completeness: Potential Host Galaxies in the 90% Credible Volume
  9. LIGO/Virgo/KAGRA S250830bp: NED Galaxies in the 4-Update Localization Volume
  10. LIGO/Virgo/KAGRA S250830bp: Updated Sky localization, EM Bright Classification, and Source Classification
  11. LIGO/Virgo/KAGRA S250830bp: Identification of a GW compact binary merger candidate
  12. EP-WXT trigger 01709200994: Liverpool Telescope upper limits
  13. GRB 250830B: Swift ToO observations
  14. EP-WXT trigger 01709200994: confirmation of a stellar flare by BOOTES-6
  15. GRB 250830B: MAXI/GSC detection
  16. LIGO/Virgo/KAGRA S250830m: Identification of a GW compact binary merger candidate
  17. GRB 250830A / MAXI J0853+337: MAXI/GSC detection
  18. The EP-WXT trigger 01709200994 is likely a flaring star
  19. GRB 250828B: Swift-BAT refined analysis
  20. EP250821a: SOAR observations
  21. EP250827a: very early ATLAS detections, starting 43 sec after the EP trigger
  22. LIGO/Virgo/KAGRA S250725j: Observations with the NSF-DOE Vera C. Rubin Observatory
  23. LIGO/Virgo/KAGRA S250818k: MeerKAT detection of an increase in radio flux from AT2025ulz
  24. GRB 250808B: SVOM detection of a burst through offline search
  25. EP250828a: refined analysis of the EP-WXT and EP-FXT observations
  26. EP250828a: Optical counterpart detection with Kinder observations
  27. EP250828a: Liverpool Telescope upper limits
  28. Swift GRB 250828B: Global MASTER-Net observations report
  29. EP250828a: Global MASTER-Net observations report
  30. EP-WXT trigger 01709200800 : KAIT optical observations
  31. EP250828a: KAIT optical upper limit
  32. EP250827a: Swift/UVOT Detection
  33. EP250828a: NOT optical counterpart confirmation
  34. EP250828a: SVOM/VT optical candidate
  35. EP250828a: Seimei/TriCCS optical counterpart detection
  36. GRB 250828B: Swift detection of a burst
  37. EP250827a: STEP/T80S Confirmation of fading optical counterpart
  38. EP250828a: Optical upper limit with Kinder observations
  39. LIGO/Virgo/KAGRA S250827fo: Updated Sky localization
  40. LIGO/Virgo/KAGRA S250818k: uGMRT 1.3 GHz observations of AT2025ulz
  41. EP250827a: LCO observations show fading optical counterpart
  42. GRB 250828A: Fermi GBM Final Localization
  43. EP250828a: Einstein Probe detection of an X-ray transient
  44. EP250827a: Preliminary analysis of the EP-WXT and EP-FXT observations
  45. GRID detection of GRB 250824A
  46. LIGO/Virgo/KAGRA S250827fo: Identification of a GW compact binary merger candidate
  47. EP250827A: VLT/X-shooter redshift confirmation
  48. Fermi GRB 250827A: Global MASTER-Net observations report
  49. EP250827a: confirmation of optical rebrightening with LCO
  50. EP250827a: GOTO observation of the optical afterglow
  51. GRB 250826A: SVOM/GRM observation
  52. GRB 250827A: Fermi GBM Final Real-time Localization
  53. EP250827A: An optical rebrightening was detected by LCO.
  54. EP250827a: Swift-XRT counterpart detection
  55. LIGO/Virgo/KAGRA S250827l: Updated Sky localization
  56. The EP-WXT trigger 01709200800 is likely a flaring star
  57. EP250827a: TRT optical observations
  58. EP250827a: BOOTES-7 early optical dectection
  59. EP250827a / GRB 250827A: MASTER-OAFA OT observation
  60. EP250827a: Gemini-South redshift z = 1.613
  61. EP250827a: Global MASTER-Net observations report
  62. EP250827a: Las Cumbres independent detection of the optical counterpart
  63. EP250827a: Gemini-South optical counterpart detection
  64. EP250827a: Einstein Probe detection of an X-ray transient
  65. LIGO/Virgo/KAGRA S250827l: Identification of a GW compact binary merger candidate
  66. Fermi GRB 250826A: Global MASTER-Net observations report
  67. GRB 250806A: HiPERCAM/GTC limits on a possible supernova
  68. EP250821a: Gemini GMOS Redshift Confirmation
  69. LIGO/Virgo/KAGRA S250818k: SAO RAS BTA z-band observations of AT2025ulz
  70. Fermi trigger No 777883624: Global MASTER-Net observations report
  71. Fermi Gamma-ray Burst Monitor trigger 777883624/250826283 is not a GRB
  72. GRB 250826A: Fermi GBM Final Real-time Localization
  73. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Confirmation of Rebrightening of AT2025ulz
  74. Fermi GRB 250824B: Global MASTER-Net observations report
  75. LIGO/Virgo/KAGRA S250818k: VLA upper limits on AT2025ulz
  76. LIGO/Virgo/KAGRA S250818k: nature of the AT2025ulz/ZTF25abjmnnps OT
  77. LIGO/Virgo/KAGRA S250818k: Pan-STARRS imaging confirms re-brightening of SN2025ulz
  78. GRB 250823A: Swift-BAT refined analysis
  79. LIGO/Virgo/KAGRA S250818k: Continued Keck I LRIS spectroscopy of ZTF25abjmnps (AT2025ulz)
  80. GRB 250821B: AstroSat CZTI detection
  81. GRB 250819A: AstroSat CZTI detection
  82. LIGO/Virgo/KAGRA S250818k: FTW Observations Show Continued Reddening of AT 2025ulz
  83. LIGO/Virgo/KAGRA S250818k: MASTER predicovery limits of the AT2025ulz/ZTF25abjmnps KN candidate
  84. GRB 250821B: Insight-HXMT detection
  85. LIGO/Virgo/KAGRA S250818k: ENGRAVE observations of SN 2025ulz as a type II supernova
  86. GRB 250823A: Swift-XRT refined Analysis
  87. EP250821a: MeerKAT radio counterpart
  88. EP triggers 01709200706 and 01709200707: GOTO confirmation of flaring stars
  89. LIGO/Virgo/KAGRA S250818k: Swift Observations of AT 2025ulz - Second Epoch
  90. GRB 250824B: Fermi GBM Final Real-time Localization
  91. The EP-WXT trigger 01709200707 is likely a flaring star
  92. GRB 250823A: COLIBRÍ optical observations
  93. The EP-WXT trigger 01709200706 is likely a flaring star
  94. GRB 250823A: SVOM/VT optical observation
  95. GRB 250824A: Fermi GBM Final Real-time Localization
  96. GRB 250823A: Swift/UVOT Detection
  97. GRB 250823A: NOT optical observations
  98. LIGO/Virgo/KAGRA S250818k: CFH/MegaCam follow-up observation for AT2025ulz
  99. LIGO/Virgo/KAGRA S250818k: COLIBRÍ confirmation of rebrightening of AT2025ulz
  100. GRB 250823A: Fermi GBM Observation

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