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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"

25876 results found.

  1. LIGO/VIRGO/KAGRA S250818k: No evidence for radio variability of AT2025ulz in MeerKAT 3 GHz data
  2. GRB 250831A (SVOM trigger sb25083102): KAIT confirmation of stellar flare
  3. Fermi-LAT Gamma-ray Observations of IceCube-250831A
  4. GRB 250902A: Fermi GBM Detection
  5. GRB 250901A: Swift/UVOT Upper Limit
  6. IceCube-250831A: Upper limits from a search for additional neutrino events in IceCube
  7. GRB 250830B: Swift-XRT afterglow detection
  8. LIGO/Virgo/KAGRA S250902av: 1 counterpart neutrino candidate event from an IceCube neutrino search
  9. LIGO/Virgo/KAGRA S250901cb: Updated Sky localization
  10. GRB 250831A (SVOM trigger sb25083102): confirmation of a stellar flare by SVOM/VT
  11. GRB 250902A: SVOM/GRM observation
  12. EP250828a: Early near-infrared follow-up with MIRAGE on the MDM 1.3m telescope
  13. EP250901a: refined analysis of the EP-WXT and EP-FXT observations
  14. IceCube-Cascade 250828A: Upper limits from a search for additional neutrino events in IceCube
  15. GRB 250901A: SVOM/VT optical afterglow with VHF data
  16. GRB 250901A: Swift-XRT afterglow detection
  17. EP250901a: Swift-XRT observations
  18. LIGO/Virgo/KAGRA S250830bp: DECam GW-MMADS candidates
  19. GRB 250901A: LCO optical upper limit
  20. LIGO/Virgo/KAGRA S250830bp: DECam DESGW Epoch 1 Candidates
  21. EP250827b: Gemini Spectroscopy 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. GRB 250830C: GECAM-B detection
  28. EP250901a: Einstein Probe detection of an X-ray transient
  29. LIGO/Virgo/KAGRA S250830m: Updated Sky localization
  30. EP250831a: Swift-XRT observations
  31. LIGO/Virgo/KAGRA S250831cc: Coverage and upper limits from MAXI/GSC observations
  32. EP250831a: EP-WXT detection of a fast X-ray transient
  33. GRB 250831A: Swift-XRT counterpart detection
  34. GRB 250831A: SVOM/COLIBRÍ (FM-GFT) optical upper limit
  35. GRB 250831A: SVOM/VT upper limit with VHF data
  36. GRB 250831A: SVOM detection of a soft burst
  37. GRB 250830B: Swift-XRT observations
  38. EP250830a/GRB 250830B: Einstein Probe detection of an X-ray transient and Swift/XRT follow-up
  39. LIGO/Virgo/KAGRA S250830bp: Coverage and upper limits from MAXI/GSC observations
  40. LIGO/Virgo/KAGRA S250830bp GLADEnet Completeness: Potential Host Galaxies in the 90% Credible Volume
  41. LIGO/Virgo/KAGRA S250830bp: NED Galaxies in the 4-Update Localization Volume
  42. LIGO/Virgo/KAGRA S250830bp: Updated Sky localization, EM Bright Classification, and Source Classification
  43. LIGO/Virgo/KAGRA S250830bp: Identification of a GW compact binary merger candidate
  44. EP-WXT trigger 01709200994: Liverpool Telescope upper limits
  45. EP-WXT trigger 01709200994: confirmation of a stellar flare by BOOTES-6
  46. GRB 250830B: MAXI/GSC detection
  47. LIGO/Virgo/KAGRA S250830m: Identification of a GW compact binary merger candidate
  48. GRB 250830A / MAXI J0853+337: MAXI/GSC detection
  49. GRB 250828B: Swift-BAT refined analysis
  50. LIGO/Virgo/KAGRA S250725j: Observations with the NSF-DOE Vera C. Rubin Observatory
  51. LIGO/Virgo/KAGRA S250818k: MeerKAT detection of an increase in radio flux from AT2025ulz
  52. EP250828a: refined analysis of the EP-WXT and EP-FXT observations
  53. EP250828a: Optical counterpart detection with Kinder observations
  54. EP250828a: Liverpool Telescope upper limits
  55. EP250828a: Global MASTER-Net observations report
  56. EP-WXT trigger 01709200800 : KAIT optical observations
  57. EP250828a: KAIT optical upper limit
  58. EP250827a: Swift/UVOT Detection
  59. EP250828a: NOT optical counterpart confirmation
  60. EP250828a: SVOM/VT optical candidate
  61. EP250828a: Seimei/TriCCS optical counterpart detection
  62. EP250828a: Optical upper limit with Kinder observations
  63. LIGO/Virgo/KAGRA S250827fo: Updated Sky localization
  64. EP250827a: LCO observations show fading optical counterpart
  65. EP250828a: Einstein Probe detection of an X-ray transient
  66. EP250827a: Preliminary analysis of the EP-WXT and EP-FXT observations
  67. LIGO/Virgo/KAGRA S250827fo: Identification of a GW compact binary merger candidate
  68. EP250827a: confirmation of optical rebrightening with LCO
  69. GRB 250826A: SVOM/GRM observation
  70. EP250827A: An optical rebrightening was detected by LCO.
  71. EP250827a: Swift-XRT counterpart detection
  72. LIGO/Virgo/KAGRA S250827l: Updated Sky localization
  73. EP250827a: TRT optical observations
  74. EP250827a: Gemini-South redshift z = 1.613
  75. EP250827a: Einstein Probe detection of an X-ray transient
  76. LIGO/Virgo/KAGRA S250827l: Identification of a GW compact binary merger candidate
  77. GRB 250806A: HiPERCAM/GTC limits on a possible supernova
  78. LIGO/Virgo/KAGRA S250818k: SAO RAS BTA z-band observations of AT2025ulz
  79. Fermi GRB 250824B: Global MASTER-Net observations report
  80. LIGO/Virgo/KAGRA S250818k: nature of the AT2025ulz/ZTF25abjmnnps OT
  81. LIGO/Virgo/KAGRA S250818k: Pan-STARRS imaging confirms re-brightening of SN2025ulz
  82. GRB 250823A: Swift-BAT refined analysis
  83. LIGO/Virgo/KAGRA S250818k: MASTER predicovery limits of the AT2025ulz/ZTF25abjmnps KN candidate
  84. LIGO/Virgo/KAGRA S250818k: ENGRAVE observations of SN 2025ulz as a type II supernova
  85. GRB 250823A: Swift-XRT refined Analysis
  86. EP250821a: MeerKAT radio counterpart
  87. GRB 250823A: COLIBRÍ optical observations
  88. GRB 250823A: SVOM/VT optical observation
  89. GRB 250823A: Swift/UVOT Detection
  90. LIGO/Virgo/KAGRA S250818k: COLIBRÍ confirmation of rebrightening of AT2025ulz
  91. GRB 250823A: Fermi GBM Observation
  92. GRB 250823A: Enhanced Swift-XRT position
  93. GRB 250823A: LCOGT Optical Detection
  94. GRB 250823A: Swift detection of a burst
  95. LIGO/Virgo/KAGRA S250818k: HST nIR detection of AT 2025ulz
  96. LIGO/Virgo/KAGRA S250818k: JinShan optical observations of AT2025ulz
  97. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Optical Detection of AT2025ulz
  98. LIGO/Virgo/KAGRA S250818k: 3 GHz MeerKAT observations of AT2025ulz
  99. GRB 250806A: Gemini observations of host galaxy candidate
  100. GRB 250821A: Kilonova-Catcher optical upper limits

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