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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"

18810 results found.

  1. EP250908c: VLT/FORS2 optical counterpart identification
  2. EP250908b: SVOM/VT optical candidate (Coordinate supplement for GCN 41758)
  3. EP250908b: SVOM/VT optical candidate
  4. EP250908c: Einstein Probe detection of an X-ray transient
  5. EP250908b: EP-WXT detection of a fast X-ray transient and EP-FXT observation
  6. Fermi-LAT Gamma-ray Observations of IceCube-250905A
  7. GRB 250903A: Swift-XRT afterglow detection
  8. LIGO/Virgo/KAGRA S250906ca: Identification of a GW compact binary merger candidate
  9. IceCube-250905A: Upper limits from a search for additional neutrino events in IceCube
  10. SVOM/sb25090605: detection of an X-ray transient from the LMXB 4U 0513-40
  11. EP250905a: Liverpool Telescope i-band upper limits
  12. LIGO/Virgo/KAGRA S250830bp: DECam/SOAR GW-MMADS updates
  13. EP250905a: Liverpool Telescope observations
  14. EP250905a: refined analysis of the EP-WXT and EP-FXT observations
  15. EP250905b: EP-WXT detection of a fast X-ray transient
  16. EP250905a: JinShan likely optical counterpart detection
  17. GRB 250905A: Swift/UVOT Upper Limits
  18. GRB 250901A - SVOM/ECLAIRs refined analysis
  19. EP250905a: Einstein Probe detection of an X-ray transient
  20. GRB250904A: Liverpool Telescope upper limits
  21. GRB 250905A: Enhanced Swift-XRT position
  22. GRB 250904A: Swift/UVOT Detection
  23. GRB 250903A: Swift/UVOT detection
  24. EP detected a brightening of LMXB 1ES 1735-26.9
  25. GRB 250905A: KAIT optical upper limit
  26. GRB 250905A: Swift detection of a burst
  27. GRB 250904A: Enhanced Swift-XRT position
  28. IceCube-Cascade 250903A: Upper limits from a search for additional neutrino events in IceCube
  29. GRB 250904A: TRT optical counterpart detection
  30. GRB 250904A: Swift detection of a burst
  31. LIGO/Virgo/KAGRA S250904cv: Identification of a GW compact binary merger candidate
  32. EP250903a: retraction of the LCO candidate, and discovery of the likely counterpart
  33. EP-WXT trigger 01709201209: Liverpool Telescope upper limits
  34. EP250903a: refined analysis of the EP-WXT and EP-FXT observations
  35. LIGO/Virgo/KAGRA S250904br: Identification of a GW compact binary merger candidate
  36. GRB 250903A: VLT X-shooter spectroscopic redshift z = 1.590
  37. LIGO/Virgo/KAGRA S250904ae: Identification of a GW compact binary merger candidate
  38. GRB 250903A: LCO optical observation
  39. GRB 250903A: LCO optical afterglow detection
  40. GRB 250903A: SVOM/VT optical confirmation with VHF data
  41. EP250901a: Mondy, Assy and SAO RAS optical limits
  42. GRB 250903A: TRT optical counterpart detection
  43. GRB 250903A: SVOM detection of a burst
  44. EP250903a: TRT optical observations
  45. EP250903a: Einstein Probe detection of an X-ray transient
  46. EP 250827B: Detection of supernova counterpart by LCO.
  47. EP250827b: NOT spectroscopic observations and AT 2025wkm classification as a broad-lined type-Ic supernova
  48. GRB 250902B: SVOM/GRM observation
  49. EP250827b: SVOM/VT observation of AT 2025wkm
  50. LIGO/VIRGO/KAGRA S250818k: No evidence for radio variability of AT2025ulz in MeerKAT 3 GHz data
  51. GRB 250831A (SVOM trigger sb25083102): KAIT confirmation of stellar flare
  52. Fermi-LAT Gamma-ray Observations of IceCube-250831A
  53. GRB 250901A: Swift/UVOT Upper Limit
  54. IceCube-250831A: Upper limits from a search for additional neutrino events in IceCube
  55. GRB 250830B: Swift-XRT afterglow detection
  56. GRB 250831A (SVOM trigger sb25083102): confirmation of a stellar flare by SVOM/VT
  57. GRB 250902A: SVOM/GRM observation
  58. EP250828a: Early near-infrared follow-up with MIRAGE on the MDM 1.3m telescope
  59. EP250901a: refined analysis of the EP-WXT and EP-FXT observations
  60. IceCube-Cascade 250828A: Upper limits from a search for additional neutrino events in IceCube
  61. GRB 250901A: SVOM/VT optical afterglow with VHF data
  62. GRB 250901A: Swift-XRT afterglow detection
  63. LIGO/Virgo/KAGRA S250830bp: DECam GW-MMADS candidates
  64. GRB 250901A: LCO optical upper limit
  65. LIGO/Virgo/KAGRA S250901cb: Identification of a GW compact binary merger candidate
  66. EP250831a: NOT optical observations and tentative afterglow candidate
  67. EP250827b: Contemporaneous detection of EP X-ray flare EP250827b and ZTF transient ZTF25abmpngy/AT2025wkm
  68. GRB 250901A: SVOM detection of a burst
  69. EP250901a: Mephisto optical upper limits
  70. GRB 250830C: AstroSat CZTI detection of a long burst
  71. EP250901a: Einstein Probe detection of an X-ray transient
  72. EP250831a: EP-WXT detection of a fast X-ray transient
  73. GRB 250831A: Swift-XRT counterpart detection
  74. GRB 250831A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  75. GRB 250831A: SVOM/VT upper limit with VHF data
  76. GRB 250831A: SVOM detection of a soft burst
  77. EP250830a/GRB 250830B: Einstein Probe detection of an X-ray transient and Swift/XRT follow-up
  78. LIGO/Virgo/KAGRA S250830bp GLADEnet Completeness: Potential Host Galaxies in the 90% Credible Volume
  79. LIGO/Virgo/KAGRA S250830bp: NED Galaxies in the 4-Update Localization Volume
  80. LIGO/Virgo/KAGRA S250830bp: Updated Sky localization, EM Bright Classification, and Source Classification
  81. LIGO/Virgo/KAGRA S250830bp: Identification of a GW compact binary merger candidate
  82. EP-WXT trigger 01709200994: Liverpool Telescope upper limits
  83. LIGO/Virgo/KAGRA S250830m: Identification of a GW compact binary merger candidate
  84. LIGO/Virgo/KAGRA S250725j: Observations with the NSF-DOE Vera C. Rubin Observatory
  85. LIGO/Virgo/KAGRA S250818k: MeerKAT detection of an increase in radio flux from AT2025ulz
  86. GRB 250808B: SVOM detection of a burst through offline search
  87. EP250828a: refined analysis of the EP-WXT and EP-FXT observations
  88. EP250828a: Optical counterpart detection with Kinder observations
  89. EP250828a: Liverpool Telescope upper limits
  90. EP-WXT trigger 01709200800 : KAIT optical observations
  91. EP250828a: KAIT optical upper limit
  92. EP250827a: Swift/UVOT Detection
  93. EP250828a: NOT optical counterpart confirmation
  94. EP250828a: SVOM/VT optical candidate
  95. EP250828a: Seimei/TriCCS optical counterpart detection
  96. EP250828a: Optical upper limit with Kinder observations
  97. EP250828a: Einstein Probe detection of an X-ray transient
  98. EP250827a: Preliminary analysis of the EP-WXT and EP-FXT observations
  99. GRID detection of GRB 250824A
  100. LIGO/Virgo/KAGRA S250827fo: Identification of a GW compact binary merger candidate

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