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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"

16159 results found.

  1. GRB 250427A: Swift-XRT refined Analysis
  2. EP250427a / GRB 250427A: LCO optical counterpart detection
  3. EP250427a / GRB 250427A: VLT/X-shooter redshift confirmation z = 1.520
  4. EP250427A/GRB250427A: Keck/LRIS redshift
  5. EP250427a: REM optical/NIR afterglow detection
  6. GRB 250424A: LCO optical observation
  7. EP250427A: COLIBRÍ Optical Detection
  8. EP250427a: TRT optical counterpart detection
  9. EP 250427a: BOOTES-7 optical afterglow candidate
  10. GRB 250424A: SVOM/GRM observation of a long burst
  11. GRB 250424A: PRIME near-infrared detection
  12. GRB 250424A: WINTER J-band detection
  13. GRB 250424A: SVOM/VT optical observation
  14. GRB 250419A: Mondy Optical Observations
  15. GRB 250424A: Swift/UVOT Detection
  16. Fermi-LAT gamma-ray observations of IceCube-250421A
  17. GRB 250424A: Skynet Optical Observations
  18. GRB 250424A: Kilonova-Catcher optical afterglow detection
  19. GRB 250419a: Continued Liverpool Telescope observations
  20. GRB 250419A: Liverpool Telescope optical upper limit
  21. GRB 250424A: COLIBRÍ Detection of a Bright Optical Counterpart
  22. GRB 250424A: BlackGEM optical afterglow detection
  23. GRB 250424A: VLT/X-shooter spectroscopic redshift z = 0.310
  24. GRB 250424A: likely host galaxy
  25. GRB 250424A: DDOTI Afterglow Detection
  26. GRB 250424A: REM optical/NIR afterglow detection
  27. GRB 250424A: Swift detection of a burst with an optical counterpart
  28. Swift GRB 250424A: Global MASTER-Net OT detection
  29. LIGO/Virgo/KAGRA S250328ae: Subaru/PFS Spectroscopic Follow up and Candidates
  30. EP250421a: Nickel optical upper limit
  31. EP250416a / GRB 250416C: Gemini GMOS-S likely host galaxy redshift z = 0.963
  32. SVOM/sb25042207: BOOTES-2 early optical upper limit
  33. SVOM/sb25042207: GOTO optical upper limits
  34. GRB250419A: VLA radio detection
  35. GRB 250419A: Mephisto Multi-band Optical Detection
  36. GRB 250419A: Calapai Observatory, Massa S. Giorgio (Messina), optical observations.
  37. IC-250421A: LAST optical observations of the IceCube neutrino candidate
  38. EP250421a: NOT optical observations
  39. GRB 250419A: Optical Observations via Virtual Telescope Project
  40. EP250421a: REM optical upper limit
  41. EP250421a: Swift/XRT counterpart detection
  42. EP250421A: COLIBRÍ Optical Upper Limit
  43. GRB 250419A: Mondy Continued Optical Observations
  44. EP250421a: Mephisto optical counterpart confirmation
  45. EP250421a: JinShan likely optical counterpart
  46. The EP-WXT trigger 01709135179: Kinder optical counterpart candidate
  47. GRB 250419A: Liverpool Telescope observations
  48. GRB 250419A: LCO optical observation
  49. GRB 250419A: JinShan optical observations
  50. GRB 250419A: SVOM/VT optical continuous observations
  51. GRB 250419A: SVOM/C-GFT optical observations
  52. GRB 250416C / EP250416a: SVOM/GRM observation of a burst
  53. GRB 250419A: LCO optical afterglow multi-band observations
  54. GRB 250419A: Mondy and AbAO Optical Observations
  55. GRB 250419A: Liverpool Telescope observations
  56. GRB 250419A: AKO Optical Afterglow Detection
  57. GRB 250419A: MASTER optical afterglow observation
  58. GRB 250407A: GTC/OSIRIS+ spectroscopic redshift z = 1.36
  59. GRB 250419A: VLT/X-shooter spectroscopic redshift z = 0.845
  60. GRB 250419A: Swift-XRT refined Analysis
  61. GRB 250419A: GOTO optical counterpart detection
  62. GRB 250419A: KAIT optical afterglow observations
  63. GRB 250419A: SVOM/VT optical bright counterpart confirmation
  64. GRB 250419A: SVOM/COLIBRÍ (FM-GFT) Detection of the Optical Counterpart
  65. GRB 250419A: SVOM detection of a soft burst
  66. EP250416a: Swift/XRT counterpart fading
  67. EP250416a: refined EP-WXT and EP-FXT analysis
  68. EP20250416a: Swift/XRT counterpart detection
  69. GRB 250403A: VLT/FORS2 spectroscopic redshift z = 1.847
  70. IceCube-250416A: DDOTI Optical Observations
  71. EP250416a: Gemini South-GMOS optical counterpart
  72. EP250225a: SVOM/VT optical brightening
  73. EP250416a: GSP optical upper limit
  74. SVOM/sb25041603: SVOM/COLIBRÍ (FM-GFT) Upper Limit on the Optical Counterpart
  75. IceCube 250414.324: DDOTI Optical Observations
  76. EP250304a: ATCA radio observations
  77. EP250404a: Nanshan 0.43m Telescope optical observatios
  78. GRB 250411A: DDOTI Optical Observations
  79. GRB 250407A: Continued KAIT/Nickel optical observations
  80. GRB 250407A: Mondy and AbAO Optical Observations
  81. EP250227a: Further NOT optical observations
  82. IceCube-250406A: Swift-XRT observations
  83. GRB 250407A: LCO detection of a fading optical counterpart
  84. GRB 250407A: SVOM/GRM observation of a bright long burst
  85. GRB 250407A: COLIBRÍ/DDRAGO Detection of the Optical Counterpart
  86. GRB 250407A: KAIT Optical Afterglow Candidate
  87. IceCube-250406A: No candidates from the Zwicky Transient Facility
  88. IceCube 250406A: DDOTI Optical Observations of the Refined Position
  89. IceCube 250406.951: COLIBRÍ/DDRAGO Optical Upper Limit
  90. IceCube 250406.951: DDOTI Optical Observations
  91. EP250404a: Multi-band Optical Observations from UCAS-70 and XL-C14
  92. GRB 250404A: Calapai Observatory, Massa S. Giorgio (Messina), optical observations.
  93. EP250404a / GRB 250404A: Montarrenti Observatory optical observations
  94. GRB 250404A / EP250404a: RC500 INASAN-Kislovodsk optical upper limit
  95. GRB 250404A / EP250404a: SVOM/GWAC-F60 and F50 observations
  96. EP250404a / GRB 250404A: J band observations by SYSU 80cm telescope
  97. GRB 250404A / EP250404a: Mondy optical observations
  98. EP250404a: refined analysis of the EP-WXT and EP-FXT observations
  99. GRB 250404A / EP250404a: GMG spectroscopic redshift at z ~ 2.627
  100. GRB 250404A / EP250404a: Leavitt Observatory optical counterpart detection

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