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 S250725j: Observations with the NSF-DOE Vera C. Rubin Observatory
  2. LIGO/Virgo/KAGRA S250818k: MeerKAT detection of an increase in radio flux from AT2025ulz
  3. GRB 250808B: SVOM detection of a burst through offline search
  4. EP250828a: refined analysis of the EP-WXT and EP-FXT observations
  5. EP250828a: Optical counterpart detection with Kinder observations
  6. EP250828a: Liverpool Telescope upper limits
  7. Swift GRB 250828B: Global MASTER-Net observations report
  8. EP250828a: Global MASTER-Net observations report
  9. EP-WXT trigger 01709200800 : KAIT optical observations
  10. EP250828a: KAIT optical upper limit
  11. EP250827a: Swift/UVOT Detection
  12. EP250828a: NOT optical counterpart confirmation
  13. EP250828a: SVOM/VT optical candidate
  14. EP250828a: Seimei/TriCCS optical counterpart detection
  15. GRB 250828B: Swift detection of a burst
  16. EP250827a: STEP/T80S Confirmation of fading optical counterpart
  17. EP250828a: Optical upper limit with Kinder observations
  18. LIGO/Virgo/KAGRA S250827fo: Updated Sky localization
  19. LIGO/Virgo/KAGRA S250818k: uGMRT 1.3 GHz observations of AT2025ulz
  20. EP250827a: LCO observations show fading optical counterpart
  21. GRB 250828A: Fermi GBM Final Localization
  22. EP250828a: Einstein Probe detection of an X-ray transient
  23. EP250827a: Preliminary analysis of the EP-WXT and EP-FXT observations
  24. GRID detection of GRB 250824A
  25. LIGO/Virgo/KAGRA S250827fo: Identification of a GW compact binary merger candidate
  26. EP250827A: VLT/X-shooter redshift confirmation
  27. Fermi GRB 250827A: Global MASTER-Net observations report
  28. EP250827a: confirmation of optical rebrightening with LCO
  29. EP250827a: GOTO observation of the optical afterglow
  30. GRB 250826A: SVOM/GRM observation
  31. GRB 250827A: Fermi GBM Final Real-time Localization
  32. EP250827A: An optical rebrightening was detected by LCO.
  33. EP250827a: Swift-XRT counterpart detection
  34. LIGO/Virgo/KAGRA S250827l: Updated Sky localization
  35. The EP-WXT trigger 01709200800 is likely a flaring star
  36. EP250827a: TRT optical observations
  37. EP250827a: BOOTES-7 early optical dectection
  38. EP250827a / GRB 250827A: MASTER-OAFA OT observation
  39. EP250827a: Gemini-South redshift z = 1.613
  40. EP250827a: Global MASTER-Net observations report
  41. EP250827a: Las Cumbres independent detection of the optical counterpart
  42. EP250827a: Gemini-South optical counterpart detection
  43. EP250827a: Einstein Probe detection of an X-ray transient
  44. LIGO/Virgo/KAGRA S250827l: Identification of a GW compact binary merger candidate
  45. Fermi GRB 250826A: Global MASTER-Net observations report
  46. GRB 250806A: HiPERCAM/GTC limits on a possible supernova
  47. EP250821a: Gemini GMOS Redshift Confirmation
  48. LIGO/Virgo/KAGRA S250818k: SAO RAS BTA z-band observations of AT2025ulz
  49. Fermi trigger No 777883624: Global MASTER-Net observations report
  50. Fermi Gamma-ray Burst Monitor trigger 777883624/250826283 is not a GRB
  51. GRB 250826A: Fermi GBM Final Real-time Localization
  52. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Confirmation of Rebrightening of AT2025ulz
  53. Fermi GRB 250824B: Global MASTER-Net observations report
  54. LIGO/Virgo/KAGRA S250818k: VLA upper limits on AT2025ulz
  55. LIGO/Virgo/KAGRA S250818k: nature of the AT2025ulz/ZTF25abjmnnps OT
  56. LIGO/Virgo/KAGRA S250818k: Pan-STARRS imaging confirms re-brightening of SN2025ulz
  57. GRB 250823A: Swift-BAT refined analysis
  58. LIGO/Virgo/KAGRA S250818k: Continued Keck I LRIS spectroscopy of ZTF25abjmnps (AT2025ulz)
  59. GRB 250821B: AstroSat CZTI detection
  60. GRB 250819A: AstroSat CZTI detection
  61. LIGO/Virgo/KAGRA S250818k: FTW Observations Show Continued Reddening of AT 2025ulz
  62. LIGO/Virgo/KAGRA S250818k: MASTER predicovery limits of the AT2025ulz/ZTF25abjmnps KN candidate
  63. GRB 250821B: Insight-HXMT detection
  64. LIGO/Virgo/KAGRA S250818k: ENGRAVE observations of SN 2025ulz as a type II supernova
  65. GRB 250823A: Swift-XRT refined Analysis
  66. EP250821a: MeerKAT radio counterpart
  67. EP triggers 01709200706 and 01709200707: GOTO confirmation of flaring stars
  68. LIGO/Virgo/KAGRA S250818k: Swift Observations of AT 2025ulz - Second Epoch
  69. GRB 250824B: Fermi GBM Final Real-time Localization
  70. The EP-WXT trigger 01709200707 is likely a flaring star
  71. GRB 250823A: COLIBRÍ optical observations
  72. The EP-WXT trigger 01709200706 is likely a flaring star
  73. GRB 250823A: SVOM/VT optical observation
  74. GRB 250824A: Fermi GBM Final Real-time Localization
  75. GRB 250823A: Swift/UVOT Detection
  76. GRB 250823A: NOT optical observations
  77. LIGO/Virgo/KAGRA S250818k: CFH/MegaCam follow-up observation for AT2025ulz
  78. LIGO/Virgo/KAGRA S250818k: COLIBRÍ confirmation of rebrightening of AT2025ulz
  79. GRB 250823A: Fermi GBM Observation
  80. GRB 250818B: MeerKAT Detection
  81. GRB 250823A: Enhanced Swift-XRT position
  82. GRB 250823A: LCOGT Optical Detection
  83. GRB 250823A: BOOTES6/DPRT early optical detection
  84. GRB 250823A: Liverpool Telescope optical detection
  85. GRB 250823A: Swift detection of a burst
  86. GRB 250823A: Fermi GBM Final Real-time Localization
  87. Swift GRB250823.84: Global MASTER-Net observations report
  88. Konus-Wind detection of GRB 250821B
  89. LIGO/Virgo/KAGRA S250818k: Rebrightening detected with Gemini/GMOS
  90. LIGO/Virgo/KAGRA S250818k: HST nIR detection of AT 2025ulz
  91. LIGO/Virgo/KAGRA S250818k: J-GEM follow-up observation for AT2025ulz
  92. LIGO/Virgo/KAGRA S250818k: PRIME nIR observations of AT2025ulz
  93. LIGO/Virgo/KAGRA S250818k: JinShan optical observations of AT2025ulz
  94. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Optical Detection of AT2025ulz
  95. LIGO/Virgo/Kagra S250818k: STEP/T80N upper limits on 2025ulz
  96. LIGO/Virgo/KAGRA S250818k: 3 GHz MeerKAT observations of AT2025ulz
  97. GRB 250806A: Gemini observations of host galaxy candidate
  98. IPN triangulation of GRB 250821B (long/bright)
  99. GRB 250821A: Kilonova-Catcher optical upper limits
  100. EP250821a: Swift/XRT counterpart fading

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