Skip to main content
New! Browse Circulars by Event, Advanced Search, Sample Codes, Schema Release. See news and announcements

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. EP250421a: Swift/XRT counterpart detection
  2. EP250421A: COLIBRÍ Optical Upper Limit
  3. GRB 250419A: Mondy Continued Optical Observations
  4. Fermi GRB 250421A: Global MASTER-Net observations report
  5. EP250421a: Global MASTER-Net observations report
  6. GRB 250421B: AstroSat CZTI detection of a bright long burst
  7. EP250421a: Einstein Probe detection of an X-ray transient
  8. EP250421a: Mephisto optical counterpart confirmation
  9. IceCube Alert 250421.71: Global MASTER-Net observations report
  10. IceCube-250421A - IceCube observation of a high-energy neutrino candidate track-like event
  11. IceCube-Cascade 250414A: Upper limits from a search for additional neutrino events in IceCube
  12. EP250421a: JinShan likely optical counterpart
  13. The EP-WXT trigger 01709135179: Kinder optical counterpart candidate
  14. GRB 250421A: Fermi GBM Final Real-time Localization
  15. GRB 250419A: Liverpool Telescope observations
  16. GRB 250419A: LCO optical observation
  17. GRB 250419A: JinShan optical observations
  18. GRB 250419A: SVOM/VT optical continuous observations
  19. GRB 250419A: SVOM/C-GFT optical observations
  20. GRB 250419A: Swift/UVOT Follow up
  21. GRB 250416C / EP250416a: SVOM/GRM observation of a burst
  22. GRB 250419A: LCO optical afterglow multi-band observations
  23. GRB 250419A: Mondy and AbAO Optical Observations
  24. GRB 250419A: Liverpool Telescope observations
  25. GRB 250419A: AKO Optical Afterglow Detection
  26. GRB 250419A: MASTER optical afterglow observation
  27. Fermi-LAT Gamma-ray Observations of IceCube-250416A
  28. GRB 250407A: rest-frame energetics from Konus-Wind observation
  29. GRB 250419A: Swift-XRT localisation
  30. GRB 250407A: GTC/OSIRIS+ spectroscopic redshift z = 1.36
  31. GRB 250419A: VLT/X-shooter spectroscopic redshift z = 0.845
  32. GRB 250419A: Swift-XRT refined Analysis
  33. GRB 250419A: GOTO optical counterpart detection
  34. GRB 250419A: KAIT optical afterglow observations
  35. GRB 250419A: SVOM/VT optical bright counterpart confirmation
  36. GRB 250419A: SVOM/COLIBRÍ (FM-GFT) Detection of the Optical Counterpart
  37. GRB 250419A: SVOM detection of a soft burst
  38. Konus-Wind detection of GRB 250416C (a counterpart of EP250416a)
  39. EP250416a: Swift/XRT counterpart fading
  40. EP250416a: refined EP-WXT and EP-FXT analysis
  41. Konus-Wind detection of GRB 250403A
  42. EP20250416a: Swift/XRT counterpart detection
  43. GRB 250403A: VLT/FORS2 spectroscopic redshift z = 1.847
  44. IceCube-250416A: DDOTI Optical Observations
  45. EP250416a: Gemini South-GMOS optical counterpart
  46. EP250225a: SVOM/VT optical brightening
  47. SVOM/sb25041603 is not a GRB
  48. EP250416a: GSP optical upper limit
  49. EP250416a: Global MASTER-Net observations report
  50. Fermi Gamma-ray Burst Monitor trigger 766505186/250416588 (GRB 250416A) is not a GRB
  51. EP250416a: Einstein Probe detection of an X-ray transient
  52. IceCube-250416A - IceCube observation of a high-energy neutrino candidate track-like event
  53. IceCube-250416A: Global MASTER-Net observations report
  54. Fermi Gamma-ray Burst Monitor trigger 766511207/250416657 is not a GRB
  55. GRB 250416B: Fermi GBM Final Real-time Localization
  56. GRB 250416A: Fermi GBM Final Real-time Localization
  57. SVOM/sb25041603: SVOM/COLIBRÍ (FM-GFT) Upper Limit on the Optical Counterpart
  58. SVOM/sb25041603: SVOM detection of an X-ray transient
  59. Fermi Gamma-ray Burst Monitor trigger 766474855/250416237 is not a GRB
  60. IceCube 250414.324: DDOTI Optical Observations
  61. GRB 250413A: AstroSat CZTI detection
  62. EP250304a: ATCA radio observations
  63. GRB 250412A: AstroSat CZTI detection
  64. EP250404a: Nanshan 0.43m Telescope optical observatios
  65. Fermi trigger No 766148493: Global MASTER-Net observations report
  66. Fermi trigger No 766173972: Global MASTER-Net observations report
  67. GRB 250411A: DDOTI Optical Observations
  68. Fermi GRB 250411A: Global MASTER-Net observations report
  69. GRB 250411A: Fermi GBM Final Real-time Localization
  70. GRB 250407A: Continued KAIT/Nickel optical observations
  71. GRB 250314A: e-MERLIN observations
  72. GRB 250407A: Mondy and AbAO Optical Observations
  73. EP250227a: Further NOT optical observations
  74. GRB 250320B: cubesat Avion detection
  75. IceCube-250406A: Swift-XRT observations
  76. IPN triangulation of GRB 250321D (consistent with the fast X-ray transient EP250321a)
  77. AMON Coincidence Alert from the sub-threshold IceCube-HAWC search NuEm-250409A
  78. IPN triangulation of GRB 250407A
  79. EP250407a: Global MASTER-Net observations report
  80. GRB 250407A: LCO detection of a fading optical counterpart
  81. Fermi-LAT gamma-ray observations of IceCube-250406A
  82. EP250407a: Swift-XRT observations
  83. IceCube-250406A: Upper limits from a search for additional neutrino events in IceCube
  84. Konus-Wind detection of GRB 250407A
  85. GRB 250407A: SVOM/GRM observation of a bright long burst
  86. GRB 250407A: EP-WXT afterglow detection
  87. EP250407a: EP-WXT detection of a fast X-ray transient
  88. GRB 250407A: COLIBRÍ/DDRAGO Detection of the Optical Counterpart
  89. GRB 250407A: KAIT Optical Afterglow Candidate
  90. IceCube-250406A: No candidates from the Zwicky Transient Facility
  91. GRB 250407A: Fermi GBM Detection
  92. GRB 250407A: Swift-XRT afterglow detection
  93. Fermi GRB 250407A: Global MASTER-Net observations report
  94. GRB 250407A: Swift ToO observations
  95. GRB 250407A: SRG/ART-XC afterglow detection
  96. LIGO/Virgo/KAGRA S250331o: Upper limits from Swift/BAT-GUANO
  97. IceCube 250406A: DDOTI Optical Observations of the Refined Position
  98. Konus-Wind detection of GRB 250406B (short/hard)
  99. IPN triangulation of GRB 250406B (short/hard)
  100. GRB 250407A: BALROG localization (Fermi Trigger 765733706 / GRB 250407659)

Advanced

Download all Circulars as a .tar.gz archive:
Questions or comments?
Contact GCN directly.
Have you found a bug in GCN?
Open an issue.
Want to contribute code to GCN?
Get involved on GitHub.

gcn.nasa.gov

A service of the Astrophysics Science Division at NASA Goddard Space Flight Center

Looking for U.S. government information and services? Visit USA.gov