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: 3 GHz MeerKAT observations of AT2025ulz
  2. GRB 250806A: Gemini observations of host galaxy candidate
  3. IPN triangulation of GRB 250821B (long/bright)
  4. GRB 250821A: Kilonova-Catcher optical upper limits
  5. EP250821a: Swift/XRT counterpart fading
  6. GRB 250812A: SVOM/ECLAIRs refined analysis
  7. GRB 250821A: Swift-BAT refined analysis
  8. LIGO/Virgo/KAGRA S250818k: Pan-STARRS coverage of the skymap and candidate counterparts
  9. LIGO/Virgo/KAGRA S250818k: NOT optical observations of AT2025ulz
  10. EP250821a: Swift/UVOT further observations.
  11. EP250821a: VLT X-shooter spectroscopic redshift z = 0.577
  12. LIGO/Virgo/KAGRA S250818k: GRAWITA TNG NIR observations of AT2025ulz
  13. GRB 250821A: VLT/FORS2 Optical Observation
  14. GRB 250821A: GECAM-B detection
  15. GRB 250821B: SVOM/GRM observation
  16. EP250821a: SVOM/VT optical observation
  17. Fermi GRB 250821B: Global MASTER-Net observations report
  18. GRB 250821A: NOT z-band upper limit
  19. GRB 250821C: Fermi GBM Final Real-time Localization
  20. GRB 250821A: KAIT optical upper limit
  21. LIGO/Virgo/KAGRA S250818k: Continued fading and reddening of AT2025ulz from Keck/LRIS imaging observations
  22. GRB 250821A: Swift-XRT refined Analysis
  23. Swift GRB 250821A: Global MASTER-Net observations report
  24. GRB 250821B: Fermi GBM Detection
  25. LIGO/Virgo/KAGRA S250818k: ENGRAVE observations of AT 2025ulz
  26. GRB 250821B: BALROG localization (Fermi Trigger / GRB 250821672)
  27. LIGO/Virgo/KAGRA S250818k : Tautenburg observations, upper limits
  28. GRB 250821B: Fermi GBM Final Localization of a Bright Burst
  29. GRB 250821A: Enhanced Swift-XRT position
  30. GRB 250821A: Swift/UVOT Upper Limits
  31. EP250821a: Rapidly fading optical source detected in Las Cumbres followup
  32. EP250821a: Swift XRT and UVOT counterpart detection
  33. LIGO/Virgo/KAGRA S250818k: GOTO counterpart search and upper limits
  34. EP250821a: Preliminary analysis of the EP-WXT and EP-FXT observations
  35. GRB 250821A: LCOGT Optical Upper Limits
  36. GRB 250814A: CMO SAI and SAO RAS izJ observations.
  37. LIGO/Virgo/KAGRA S250818k: 10 GHz VLA observations of AT2025ulz
  38. GRB 250821A: Prompt enhanced Swift-XRT position
  39. GRB 250821A: Swift detection of a burst
  40. LIGO/Virgo/KAGRA S250818k: WFST pre-discovery limits and follow-up observations of AT 2025ulz
  41. LIGO/Virgo/KAGRA S250818k: EP/FXT observation of AT 2025ulz
  42. EP250821a: Einstein Probe detection of an X-ray transient
  43. GRB 250819A: SVOM/GRM observation of a possible “long” duration type I burst
  44. GRB 250819A: Insight-HXMT detection
  45. LIGO/Virgo/KAGRA S250818k: WINTER J-band observations of AT 2025ulz
  46. GRB 250818B: 10 GHz VLA detection
  47. LIGO/Virgo/KAGRA S250818k: Pan-STARRS grizy-band imaging and photometry of AT2025ulz
  48. LIGO/Virgo/KAGRA S250818k: Swift observations of AT 2025ulz
  49. LIGO/Virgo/KAGRA S250818k: Multi-band Gemini GMOS Detections
  50. LIGO/Virgo/KAGRA S250818k: ATLAS pre-discovery limits for AT2025ulz
  51. GRB 250814A: Swift/UVOT Upper Limits
  52. GRB 250813B: Swift/UVOT Upper Limit
  53. IPN triangulation of GRB 250816A (short)
  54. IPN triangulation of GRB 250814C (short)
  55. IPN triangulation of GRB 250804B (short)
  56. GRB 250818B: FTW optical and NIR observations show reddening of the counterpart
  57. GRB 250818B: Kilonova-Catcher optical afterglow detection
  58. LIGO/Virgo/KAGRA S250818k: AstroSat CZTI non-detection and upper limits
  59. GRB 250818B: Liverpool Telescope optical detections
  60. LIGO/Virgo/KAGRA S250818k: Upper limits from Fermi-GBM Observations
  61. LIGO/Virgo/KAGRA S250818k: Updated Sky localization and EM Bright Classification
  62. LIGO/Virgo/KAGRA S250818k: Pan-STARRS pre-detection limits for AT2025ulz
  63. GRB 250818A: AstroSat CZTI detection
  64. LIGO/Virgo/KAGRA S250818k: Properties of the low-significance GW compact binary merger candidate potentially associated with AT 2025ulz
  65. LIGO/Virgo/KAGRA S250818k: Keck I LRIS spectroscopy of ZTF25abjmnps (AT2025ulz)
  66. GRB 250818B: Swift/UVOT Detection
  67. Fermi Gamma-ray Burst Monitor trigger 777342746/250820022 is not a GRB
  68. LIGO/Virgo/KAGRA S250818k: FTW Fast reddening of AT 2025ulz
  69. GRB 250820A: Fermi GBM Final Real-time Localization
  70. GRB 250818B: optical afterglow detection with Lesedi (GOTO25fzq)
  71. GRB 250818B: TRT Optical Observation
  72. Fermi GRB 250816A: Global MASTER-Net observations report
  73. GRB 250818B: SAO RAS optical observations
  74. Swift GRB 250818A: Global MASTER-Net observations report
  75. GRB 250818B: NOT optical observations
  76. GRB 250818A: Swift-XRT refined Analysis
  77. GRB 250818B: EP-FXT counterpart detection
  78. GRB 250818A: Swift-BAT refined analysis
  79. Fermi Gamma-ray Burst Monitor trigger 777251788/250818970 is not a GRB
  80. LIGO/Virgo/KAGRA S250818k: FTW optical and NIR observations of AT 2025ulz
  81. GRB 250818C: Fermi GBM Final Real-time Localization
  82. GRB 250818B: Keck redshift of the optical afterglow
  83. Fermi trigger No 776849714: Global MASTER-Net observations report
  84. GRB 250818B: KAIT optical observations
  85. GRB 250818A: Swift/UVOT Upper Limits
  86. LIGO/Virgo/KAGRA S250818t: Updated Sky localization
  87. LIGO/Virgo/KAGRA S250818k: Candidates from the Zwicky Transient Facility
  88. GRB 250818A: Enhanced Swift-XRT position
  89. GRB 250813B: SVOM/ECLAIRs refined analysis
  90. GRB 250818A: Fermi GBM Observation
  91. LIGO/Virgo/KAGRA S250818k: Coverage and upper limits from MAXI/GSC observations
  92. GRB 250818B: SVOM/VT optical observation
  93. GRB 250814A: Further GRAWITA TNG NIR observations
  94. GRB 250818B: Swift-XRT afterglow detection
  95. GRB 250818B: GOTO optical counterpart candidate
  96. GRB 250818B: SVOM detection of a short burst
  97. LIGO/Virgo/KAGRA S250818t: Identification of a GW compact binary merger candidate
  98. GRB 250818A: Swift detection of a burst
  99. GRB 250818A: Fermi GBM Final Real-time Localization
  100. sb25081602: Swift-XRT observations

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