Skip to main content
Retirement of GCN Classic VOEvent Brokers. 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. LIGO/Virgo/KAGRA S250818k: GRAWITA TNG NIR observations of AT2025ulz
  2. GRB 250821A: VLT/FORS2 Optical Observation
  3. GRB 250821A: GECAM-B detection
  4. GRB 250821B: SVOM/GRM observation
  5. EP250821a: SVOM/VT optical observation
  6. Fermi GRB 250821B: Global MASTER-Net observations report
  7. GRB 250821A: NOT z-band upper limit
  8. GRB 250821C: Fermi GBM Final Real-time Localization
  9. GRB 250821A: KAIT optical upper limit
  10. LIGO/Virgo/KAGRA S250818k: Continued fading and reddening of AT2025ulz from Keck/LRIS imaging observations
  11. GRB 250821A: Swift-XRT refined Analysis
  12. Swift GRB 250821A: Global MASTER-Net observations report
  13. GRB 250821B: Fermi GBM Detection
  14. LIGO/Virgo/KAGRA S250818k: ENGRAVE observations of AT 2025ulz
  15. GRB 250821B: BALROG localization (Fermi Trigger / GRB 250821672)
  16. LIGO/Virgo/KAGRA S250818k : Tautenburg observations, upper limits
  17. GRB 250821B: Fermi GBM Final Localization of a Bright Burst
  18. GRB 250821A: Enhanced Swift-XRT position
  19. GRB 250821A: Swift/UVOT Upper Limits
  20. EP250821a: Rapidly fading optical source detected in Las Cumbres followup
  21. EP250821a: Swift XRT and UVOT counterpart detection
  22. LIGO/Virgo/KAGRA S250818k: GOTO counterpart search and upper limits
  23. EP250821a: Preliminary analysis of the EP-WXT and EP-FXT observations
  24. GRB 250821A: LCOGT Optical Upper Limits
  25. GRB 250814A: CMO SAI and SAO RAS izJ observations.
  26. LIGO/Virgo/KAGRA S250818k: 10 GHz VLA observations of AT2025ulz
  27. GRB 250821A: Prompt enhanced Swift-XRT position
  28. GRB 250821A: Swift detection of a burst
  29. LIGO/Virgo/KAGRA S250818k: WFST pre-discovery limits and follow-up observations of AT 2025ulz
  30. LIGO/Virgo/KAGRA S250818k: EP/FXT observation of AT 2025ulz
  31. EP250821a: Einstein Probe detection of an X-ray transient
  32. GRB 250819A: SVOM/GRM observation of a possible “long” duration type I burst
  33. GRB 250819A: Insight-HXMT detection
  34. LIGO/Virgo/KAGRA S250818k: WINTER J-band observations of AT 2025ulz
  35. GRB 250818B: 10 GHz VLA detection
  36. LIGO/Virgo/KAGRA S250818k: Pan-STARRS grizy-band imaging and photometry of AT2025ulz
  37. LIGO/Virgo/KAGRA S250818k: Swift observations of AT 2025ulz
  38. LIGO/Virgo/KAGRA S250818k: Multi-band Gemini GMOS Detections
  39. LIGO/Virgo/KAGRA S250818k: ATLAS pre-discovery limits for AT2025ulz
  40. GRB 250814A: Swift/UVOT Upper Limits
  41. GRB 250813B: Swift/UVOT Upper Limit
  42. IPN triangulation of GRB 250816A (short)
  43. IPN triangulation of GRB 250814C (short)
  44. IPN triangulation of GRB 250804B (short)
  45. GRB 250818B: FTW optical and NIR observations show reddening of the counterpart
  46. GRB 250818B: Kilonova-Catcher optical afterglow detection
  47. LIGO/Virgo/KAGRA S250818k: AstroSat CZTI non-detection and upper limits
  48. GRB 250818B: Liverpool Telescope optical detections
  49. LIGO/Virgo/KAGRA S250818k: Upper limits from Fermi-GBM Observations
  50. LIGO/Virgo/KAGRA S250818k: Updated Sky localization and EM Bright Classification
  51. LIGO/Virgo/KAGRA S250818k: Pan-STARRS pre-detection limits for AT2025ulz
  52. GRB 250818A: AstroSat CZTI detection
  53. LIGO/Virgo/KAGRA S250818k: Properties of the low-significance GW compact binary merger candidate potentially associated with AT 2025ulz
  54. LIGO/Virgo/KAGRA S250818k: Keck I LRIS spectroscopy of ZTF25abjmnps (AT2025ulz)
  55. GRB 250818B: Swift/UVOT Detection
  56. Fermi Gamma-ray Burst Monitor trigger 777342746/250820022 is not a GRB
  57. LIGO/Virgo/KAGRA S250818k: FTW Fast reddening of AT 2025ulz
  58. GRB 250820A: Fermi GBM Final Real-time Localization
  59. GRB 250818B: optical afterglow detection with Lesedi (GOTO25fzq)
  60. GRB 250818B: TRT Optical Observation
  61. Fermi GRB 250816A: Global MASTER-Net observations report
  62. GRB 250818B: SAO RAS optical observations
  63. Swift GRB 250818A: Global MASTER-Net observations report
  64. GRB 250818B: NOT optical observations
  65. GRB 250818A: Swift-XRT refined Analysis
  66. GRB 250818B: EP-FXT counterpart detection
  67. GRB 250818A: Swift-BAT refined analysis
  68. Fermi Gamma-ray Burst Monitor trigger 777251788/250818970 is not a GRB
  69. LIGO/Virgo/KAGRA S250818k: FTW optical and NIR observations of AT 2025ulz
  70. GRB 250818C: Fermi GBM Final Real-time Localization
  71. GRB 250818B: Keck redshift of the optical afterglow
  72. Fermi trigger No 776849714: Global MASTER-Net observations report
  73. GRB 250818B: KAIT optical observations
  74. GRB 250818A: Swift/UVOT Upper Limits
  75. LIGO/Virgo/KAGRA S250818t: Updated Sky localization
  76. LIGO/Virgo/KAGRA S250818k: Candidates from the Zwicky Transient Facility
  77. GRB 250818A: Enhanced Swift-XRT position
  78. GRB 250813B: SVOM/ECLAIRs refined analysis
  79. GRB 250818A: Fermi GBM Observation
  80. LIGO/Virgo/KAGRA S250818k: Coverage and upper limits from MAXI/GSC observations
  81. GRB 250818B: SVOM/VT optical observation
  82. GRB 250814A: Further GRAWITA TNG NIR observations
  83. GRB 250818B: Swift-XRT afterglow detection
  84. GRB 250818B: GOTO optical counterpart candidate
  85. GRB 250818B: SVOM detection of a short burst
  86. LIGO/Virgo/KAGRA S250818t: Identification of a GW compact binary merger candidate
  87. GRB 250818A: Swift detection of a burst
  88. GRB 250818A: Fermi GBM Final Real-time Localization
  89. sb25081602: Swift-XRT observations
  90. GRB 250816A: SVOM/GRM observation of a short burst
  91. SVOM/sb25081602: detection of a likely X-ray transient
  92. Fermi GRB 250814B: Global MASTER-Net observations report
  93. GRB 250816A: Fermi GBM Final Real-time Localization
  94. GRB 250814A: Swift-BAT refined analysis
  95. GRB 250815A: Fermi GBM Final Localization
  96. GRB 250813B: Liverpool Telescope optical upper limits
  97. GRB 250814A: Further COLIBRÍ optical upper limit
  98. GRB 250814A: detection of the afterglow candidate with Liverpool Telescope
  99. GRB 250814A: GRAWITA TNG NIR observations
  100. GRB 250812A: SVOM/VT optical continued observation

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