Skip to main content
End of Swift Science Operations, CHIME Notices Unavailable During Upgrade. See news and announcements

GCN Circulars

GCN Circulars are rapid bulletins submitted by and distributed to the community. 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 250818B: MeerKAT Detection
  2. GRB 250823A: Enhanced Swift-XRT position
  3. GRB 250823A: LCOGT Optical Detection
  4. GRB 250823A: BOOTES6/DPRT early optical detection
  5. GRB 250823A: Liverpool Telescope optical detection
  6. GRB 250823A: Swift detection of a burst
  7. GRB 250823A: Fermi GBM Final Real-time Localization
  8. Swift GRB250823.84: Global MASTER-Net observations report
  9. Konus-Wind detection of GRB 250821B
  10. LIGO/Virgo/KAGRA S250818k: Rebrightening detected with Gemini/GMOS
  11. LIGO/Virgo/KAGRA S250818k: HST nIR detection of AT 2025ulz
  12. LIGO/Virgo/KAGRA S250818k: J-GEM follow-up observation for AT2025ulz
  13. LIGO/Virgo/KAGRA S250818k: PRIME nIR observations of AT2025ulz
  14. LIGO/Virgo/KAGRA S250818k: JinShan optical observations of AT2025ulz
  15. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Optical Detection of AT2025ulz
  16. LIGO/Virgo/Kagra S250818k: STEP/T80N upper limits on 2025ulz
  17. LIGO/Virgo/KAGRA S250818k: 3 GHz MeerKAT observations of AT2025ulz
  18. GRB 250806A: Gemini observations of host galaxy candidate
  19. IPN triangulation of GRB 250821B (long/bright)
  20. GRB 250821A: Kilonova-Catcher optical upper limits
  21. EP250821a: Swift/XRT counterpart fading
  22. GRB 250812A: SVOM/ECLAIRs refined analysis
  23. GRB 250821A: Swift-BAT refined analysis
  24. LIGO/Virgo/KAGRA S250818k: Pan-STARRS coverage of the skymap and candidate counterparts
  25. LIGO/Virgo/KAGRA S250818k: NOT optical observations of AT2025ulz
  26. EP250821a: Swift/UVOT further observations.
  27. EP250821a: VLT X-shooter spectroscopic redshift z = 0.577
  28. LIGO/Virgo/KAGRA S250818k: GRAWITA TNG NIR observations of AT2025ulz
  29. GRB 250821A: VLT/FORS2 Optical Observation
  30. GRB 250821A: GECAM-B detection
  31. GRB 250821B: SVOM/GRM observation
  32. EP250821a: SVOM/VT optical observation
  33. Fermi GRB 250821B: Global MASTER-Net observations report
  34. GRB 250821A: NOT z-band upper limit
  35. GRB 250821C: Fermi GBM Final Real-time Localization
  36. GRB 250821A: KAIT optical upper limit
  37. LIGO/Virgo/KAGRA S250818k: Continued fading and reddening of AT2025ulz from Keck/LRIS imaging observations
  38. GRB 250821A: Swift-XRT refined Analysis
  39. Swift GRB 250821A: Global MASTER-Net observations report
  40. GRB 250821B: Fermi GBM Detection
  41. LIGO/Virgo/KAGRA S250818k: ENGRAVE observations of AT 2025ulz
  42. GRB 250821B: BALROG localization (Fermi Trigger / GRB 250821672)
  43. LIGO/Virgo/KAGRA S250818k : Tautenburg observations, upper limits
  44. GRB 250821B: Fermi GBM Final Localization of a Bright Burst
  45. GRB 250821A: Enhanced Swift-XRT position
  46. GRB 250821A: Swift/UVOT Upper Limits
  47. EP250821a: Rapidly fading optical source detected in Las Cumbres followup
  48. EP250821a: Swift XRT and UVOT counterpart detection
  49. LIGO/Virgo/KAGRA S250818k: GOTO counterpart search and upper limits
  50. EP250821a: Preliminary analysis of the EP-WXT and EP-FXT observations
  51. GRB 250821A: LCOGT Optical Upper Limits
  52. GRB 250814A: CMO SAI and SAO RAS izJ observations.
  53. LIGO/Virgo/KAGRA S250818k: 10 GHz VLA observations of AT2025ulz
  54. GRB 250821A: Prompt enhanced Swift-XRT position
  55. GRB 250821A: Swift detection of a burst
  56. LIGO/Virgo/KAGRA S250818k: WFST pre-discovery limits and follow-up observations of AT 2025ulz
  57. LIGO/Virgo/KAGRA S250818k: EP/FXT observation of AT 2025ulz
  58. EP250821a: Einstein Probe detection of an X-ray transient
  59. GRB 250819A: SVOM/GRM observation of a possible “long” duration type I burst
  60. GRB 250819A: Insight-HXMT detection
  61. LIGO/Virgo/KAGRA S250818k: WINTER J-band observations of AT 2025ulz
  62. GRB 250818B: 10 GHz VLA detection
  63. LIGO/Virgo/KAGRA S250818k: Pan-STARRS grizy-band imaging and photometry of AT2025ulz
  64. LIGO/Virgo/KAGRA S250818k: Swift observations of AT 2025ulz
  65. LIGO/Virgo/KAGRA S250818k: Multi-band Gemini GMOS Detections
  66. LIGO/Virgo/KAGRA S250818k: ATLAS pre-discovery limits for AT2025ulz
  67. GRB 250814A: Swift/UVOT Upper Limits
  68. GRB 250813B: Swift/UVOT Upper Limit
  69. IPN triangulation of GRB 250816A (short)
  70. IPN triangulation of GRB 250814C (short)
  71. IPN triangulation of GRB 250804B (short)
  72. GRB 250818B: FTW optical and NIR observations show reddening of the counterpart
  73. GRB 250818B: Kilonova-Catcher optical afterglow detection
  74. LIGO/Virgo/KAGRA S250818k: AstroSat CZTI non-detection and upper limits
  75. GRB 250818B: Liverpool Telescope optical detections
  76. LIGO/Virgo/KAGRA S250818k: Upper limits from Fermi-GBM Observations
  77. LIGO/Virgo/KAGRA S250818k: Updated Sky localization and EM Bright Classification
  78. LIGO/Virgo/KAGRA S250818k: Pan-STARRS pre-detection limits for AT2025ulz
  79. GRB 250818A: AstroSat CZTI detection
  80. LIGO/Virgo/KAGRA S250818k: Properties of the low-significance GW compact binary merger candidate potentially associated with AT 2025ulz
  81. LIGO/Virgo/KAGRA S250818k: Keck I LRIS spectroscopy of ZTF25abjmnps (AT2025ulz)
  82. GRB 250818B: Swift/UVOT Detection
  83. Fermi Gamma-ray Burst Monitor trigger 777342746/250820022 is not a GRB
  84. LIGO/Virgo/KAGRA S250818k: FTW Fast reddening of AT 2025ulz
  85. GRB 250820A: Fermi GBM Final Real-time Localization
  86. GRB 250818B: optical afterglow detection with Lesedi (GOTO25fzq)
  87. GRB 250818B: TRT Optical Observation
  88. Fermi GRB 250816A: Global MASTER-Net observations report
  89. GRB 250818B: SAO RAS optical observations
  90. Swift GRB 250818A: Global MASTER-Net observations report
  91. GRB 250818B: NOT optical observations
  92. GRB 250818A: Swift-XRT refined Analysis
  93. GRB 250818B: EP-FXT counterpart detection
  94. GRB 250818A: Swift-BAT refined analysis
  95. Fermi Gamma-ray Burst Monitor trigger 777251788/250818970 is not a GRB
  96. LIGO/Virgo/KAGRA S250818k: FTW optical and NIR observations of AT 2025ulz
  97. GRB 250818C: Fermi GBM Final Real-time Localization
  98. GRB 250818B: Keck redshift of the optical afterglow
  99. Fermi trigger No 776849714: Global MASTER-Net observations report
  100. GRB 250818B: KAIT optical observations

Advanced

Download all Circulars as a .tar.gz archive (updated once a day):
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