Skip to main content
Due to the lapse in federal government funding, NASA is not updating this website. See the Operations FAQ for GCN impacts.
New! Super-Kamiokande JSON Notices and Schema v4.5.0. 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"

21839 results found.

  1. EP250903a: TRT optical observations
  2. EP250903a: Einstein Probe detection of an X-ray transient
  3. EP 250827B: Detection of supernova counterpart by LCO.
  4. EP/WXT01709201159: GOTO optical follow-up
  5. GRB 250902B: SVOM/GRM observation
  6. EP250827b: SVOM/VT observation of AT 2025wkm
  7. LIGO/VIRGO/KAGRA S250818k: No evidence for radio variability of AT2025ulz in MeerKAT 3 GHz data
  8. GRB 250831A (SVOM trigger sb25083102): KAIT confirmation of stellar flare
  9. GRB 250901A: Swift/UVOT Upper Limit
  10. GRB 250830B: Swift-XRT afterglow detection
  11. LIGO/Virgo/KAGRA S250902av: 1 counterpart neutrino candidate event from an IceCube neutrino search
  12. GRB 250831A (SVOM trigger sb25083102): confirmation of a stellar flare by SVOM/VT
  13. GRB 250902A: SVOM/GRM observation
  14. EP250828a: Early near-infrared follow-up with MIRAGE on the MDM 1.3m telescope
  15. EP250901a: refined analysis of the EP-WXT and EP-FXT observations
  16. GRB 250901A: SVOM/VT optical afterglow with VHF data
  17. GRB 250901A: Swift-XRT afterglow detection
  18. EP250901a: Swift-XRT observations
  19. LIGO/Virgo/KAGRA S250830bp: DECam GW-MMADS candidates
  20. GRB 250901A: LCO optical upper limit
  21. EP250827b: Swift observations of AT 2025wkm
  22. LIGO/Virgo/KAGRA S250901cb: Identification of a GW compact binary merger candidate
  23. EP250831a: NOT optical observations and tentative afterglow candidate
  24. EP250827b: Contemporaneous detection of EP X-ray flare EP250827b and ZTF transient ZTF25abmpngy/AT2025wkm
  25. GRB 250901A: SVOM detection of a burst
  26. EP250901a: Mephisto optical upper limits
  27. EP250901a: Einstein Probe detection of an X-ray transient
  28. EP250831a: Swift-XRT observations
  29. EP250831a: EP-WXT detection of a fast X-ray transient
  30. GRB 250831A: Swift-XRT counterpart detection
  31. GRB 250831A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  32. GRB 250831A: SVOM/VT upper limit with VHF data
  33. GRB 250831A: SVOM detection of a soft burst
  34. GRB 250830B: Swift-XRT observations
  35. EP250830a/GRB 250830B: Einstein Probe detection of an X-ray transient and Swift/XRT follow-up
  36. LIGO/Virgo/KAGRA S250830bp: Coverage and upper limits from MAXI/GSC observations
  37. LIGO/Virgo/KAGRA S250830bp GLADEnet Completeness: Potential Host Galaxies in the 90% Credible Volume
  38. LIGO/Virgo/KAGRA S250830bp: Updated Sky localization, EM Bright Classification, and Source Classification
  39. LIGO/Virgo/KAGRA S250830bp: Identification of a GW compact binary merger candidate
  40. EP-WXT trigger 01709200994: Liverpool Telescope upper limits
  41. LIGO/Virgo/KAGRA S250830m: Identification of a GW compact binary merger candidate
  42. LIGO/Virgo/KAGRA S250725j: Observations with the NSF-DOE Vera C. Rubin Observatory
  43. LIGO/Virgo/KAGRA S250818k: MeerKAT detection of an increase in radio flux from AT2025ulz
  44. EP250828a: refined analysis of the EP-WXT and EP-FXT observations
  45. EP250828a: Optical counterpart detection with Kinder observations
  46. EP250828a: Liverpool Telescope upper limits
  47. EP-WXT trigger 01709200800 : KAIT optical observations
  48. EP250828a: KAIT optical upper limit
  49. EP250827a: Swift/UVOT Detection
  50. EP250828a: NOT optical counterpart confirmation
  51. EP250828a: SVOM/VT optical candidate
  52. EP250828a: Seimei/TriCCS optical counterpart detection
  53. GRB 250828B: Swift detection of a burst
  54. EP250828a: Optical upper limit with Kinder observations
  55. LIGO/Virgo/KAGRA S250818k: uGMRT 1.3 GHz observations of AT2025ulz
  56. EP250828a: Einstein Probe detection of an X-ray transient
  57. EP250827a: Preliminary analysis of the EP-WXT and EP-FXT observations
  58. LIGO/Virgo/KAGRA S250827fo: Identification of a GW compact binary merger candidate
  59. EP250827a: confirmation of optical rebrightening with LCO
  60. GRB 250826A: SVOM/GRM observation
  61. EP250827A: An optical rebrightening was detected by LCO.
  62. EP250827a: Swift-XRT counterpart detection
  63. EP250827a: TRT optical observations
  64. EP250827a: Einstein Probe detection of an X-ray transient
  65. LIGO/Virgo/KAGRA S250827l: Identification of a GW compact binary merger candidate
  66. GRB 250806A: HiPERCAM/GTC limits on a possible supernova
  67. LIGO/Virgo/KAGRA S250818k: SAO RAS BTA z-band observations of AT2025ulz
  68. Fermi GRB 250824B: Global MASTER-Net observations report
  69. LIGO/Virgo/KAGRA S250818k: VLA upper limits on AT2025ulz
  70. LIGO/Virgo/KAGRA S250818k: Pan-STARRS imaging confirms re-brightening of SN2025ulz
  71. LIGO/Virgo/KAGRA S250818k: MASTER predicovery limits of the AT2025ulz/ZTF25abjmnps KN candidate
  72. LIGO/Virgo/KAGRA S250818k: ENGRAVE observations of SN 2025ulz as a type II supernova
  73. GRB 250823A: Swift-XRT refined Analysis
  74. EP250821a: MeerKAT radio counterpart
  75. LIGO/Virgo/KAGRA S250818k: Swift Observations of AT 2025ulz - Second Epoch
  76. GRB 250823A: COLIBRÍ optical observations
  77. GRB 250823A: SVOM/VT optical observation
  78. GRB 250823A: Swift/UVOT Detection
  79. LIGO/Virgo/KAGRA S250818k: COLIBRÍ confirmation of rebrightening of AT2025ulz
  80. GRB 250823A: Enhanced Swift-XRT position
  81. GRB 250823A: LCOGT Optical Detection
  82. GRB 250823A: Swift detection of a burst
  83. LIGO/Virgo/KAGRA S250818k: HST nIR detection of AT 2025ulz
  84. LIGO/Virgo/KAGRA S250818k: PRIME nIR observations of AT2025ulz
  85. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Optical Detection of AT2025ulz
  86. LIGO/Virgo/Kagra S250818k: STEP/T80N upper limits on 2025ulz
  87. LIGO/Virgo/KAGRA S250818k: 3 GHz MeerKAT observations of AT2025ulz
  88. IPN triangulation of GRB 250821B (long/bright)
  89. GRB 250821A: Kilonova-Catcher optical upper limits
  90. EP250821a: Swift/XRT counterpart fading
  91. GRB 250812A: SVOM/ECLAIRs refined analysis
  92. LIGO/Virgo/KAGRA S250818k: Pan-STARRS coverage of the skymap and candidate counterparts
  93. EP250821a: Swift/UVOT further observations.
  94. GRB 250821A: VLT/FORS2 Optical Observation
  95. GRB 250821B: SVOM/GRM observation
  96. EP250821a: SVOM/VT optical observation
  97. GRB 250821A: NOT z-band upper limit
  98. GRB 250821A: KAIT optical upper limit
  99. GRB 250821A: Swift-XRT refined Analysis
  100. LIGO/Virgo/KAGRA S250818k : Tautenburg observations, upper limits

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