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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.

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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').
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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.

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subject:"Swift"
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10922 results found.

  1. GRB 260310A / AT2026fgk: photometric monitoring and tentative maximum of a possible SN
  2. EP260416a: Mondy and Terskol optical upper limits
  3. EP260321a/SN 2026gzf: spectroscopy at Mondy observatory
  4. GRB 260401A: cubesat Avion detection
  5. The EP-WXT trigger 01709258652: Mondy optical observations
  6. GRB 250328A: VLT host galaxy discovery and redshift z = 1.250
  7. EP260416a: Mondy optical observations
  8. EP260416a: ZTSh R band observations
  9. EP250512a / GRB 250512B: VLT/X-shooter host galaxy identification and redshift z = 1.773
  10. GRB 250530A: VLT/X-shooter host galaxy redshift z = 1.486
  11. GRB 260421B: SVOM/VT optical observations
  12. GRB 260415A: CALET Gamma-Ray Burst Monitor detection
  13. GRB 260415B: CALET Gamma-Ray Burst Monitor detection
  14. GRB 260421B: VLT/X-shooter spectroscopic redshift z = 2.115
  15. EP260416a: Optical follow-up observations with Kinder
  16. GOTO26djh/AT2026jpw: CrAO and Mondy optical observations of the transient
  17. EP260416a: VLT/FORS2 spectroscopic redshift confirmation
  18. GOTO26djh/AT2026jpw: ZTSh R,I bands observations of the transient
  19. EP260416a: SVOM/VT optical observation
  20. GOTO26djh/AT2026jpw: SVOM/VT optical observation
  21. GOTO26djh/AT2026jpw transient: SAO RAS optical observations
  22. NOT r-band observations of the transient GOTO26djh/AT2026jpw
  23. EP260321a: CMO SAI J,K observations
  24. EP260321a: SVOM/VT optical observations and color changes around peak
  25. GRB 260410A: CALET Gamma-Ray Burst Monitor detection
  26. The EP-WXT trigger 01709260010 is likely a flaring star
  27. GRB 260411B: Fermi-LAT detection
  28. EP-WXT01709259790: Optical Upper limits with kinder observations
  29. EP260409a: SVOM/VT optical upper limits
  30. GRB 260407A: CALET Gamma-Ray Burst Monitor detection
  31. EP260321a: VLA radio detection
  32. EP260405a: GMOS-N optical upper limits
  33. EP260405a: SVOM/VT optical upper limits
  34. GRB 260330B: SVOM/VT further optical observation
  35. EP260403a: LCO optical observations of the counterpart
  36. GRB 260330B: SVOM/VT optical candidate
  37. GRB 260402A / EP260402a: SVOM/VT optical upper limits
  38. GRB 260401A: CALET Gamma-Ray Burst Monitor detection
  39. GRB 260401A: MAXI/GSC detection
  40. EP260329b: Mondy and Assy-Turgen optical upper limits
  41. GRB 260330B: SVOM/VT optical upper limits
  42. EP260329b: Optical follow-up with Kinder observations
  43. EP260329a: Optical upper limit with Kinder observations
  44. EP260327a: SVOM/VT optical upper limits
  45. EP260327a: Gemini-North optical upper limits
  46. GRB 260310A: OSIRIS+/GTC spectroscopic detection of the associated BL-Ic, SN 2026fgk
  47. GRB 260310A / AT2026fgk: Late-time infrared detection with MIRAGE on the MDM 1.3m telescope
  48. EP260321a: VLT/FORS2 spectroscopy confirmation of an associated type Ic-BL supernova SN 2026gzf
  49. GRB 260310A: LBT optical observations
  50. EP260321A: Mondy optical observations
  51. GRB 260316B: CALET Gamma-Ray Burst Monitor detection
  52. EP260321a / AT2026gzf: VLT/X-shooter detection of supernova-like spectral features at z = 0.0344
  53. EP260321a: Continued brightening from Kinder follow-up of the emerging supernova candidate
  54. EP260321a: VLT imaging and spectroscopy show the variable source to be at z = 0.0343
  55. EP260321a: further Kinder optical observations
  56. GRB 260321A: SVOM/VT optical upper limits
  57. EP260321a: SVOM/VT optical upper limit
  58. GRB 260310A: continued optical observation at Mondy
  59. EP260321a: Kinder observations detect a blue variable star and set limits on a source from the z =0.034 galaxy within the error circle
  60. GRB 260310A: no evidence of re-brightening up to 9.6 days in optical observation at Mondy
  61. GRB 260310A/AT2026fgk: LBT near-infrared observations
  62. GRB 260310A / AT 2026fgk: radio detection with the VLA
  63. GRB 260310A / AT2026fgk: SVOM/VT optical observations
  64. IceCube-260315A/AT2026fpm: EP-FXT follow-up observation
  65. EP260316a / GRB 260316A: SVOM/VT optical upper limits
  66. EP260316a: optical upper limit with Kinder observations
  67. EP260314a: optical upper limit with Kinder observations
  68. EP260314a: SVOM/VT optical candidate
  69. GRB 260310A / AT2026fgk: SAO RAS optical observations
  70. GRB 260310A / AT2026fgk: Multiband optical follow-up with Kinder observations
  71. GRB 260310A: NOT optical polarimetry
  72. GRB 260310A/AT 2026fgk: Bok spectroscopic observation
  73. GRB 260310A / AT2026fgk: OSIRIS+/GTC spectroscopy confirms redshift z = 0.153
  74. GRB 260307A: CALET Gamma-Ray Burst Monitor detection
  75. GRB 260312A: Swift detection of a burst
  76. GRB 260131A/B: radio detection with the VLA
  77. EP260306a: Mondy optical upper limit
  78. GRB 260208A: radio detection with the VLA
  79. GRB 260307B: SVOM/VT upper limit with X band data analysis
  80. GRB 260307B: SVOM/VT optical candidate
  81. EP260302a: SVOM/VT optical observation
  82. EP260306a: Gemini-North redshift z = 4.773
  83. EP260306a: SVOM/VT optical observation
  84. EP260302a: Gemini-South redshift z = 1.535
  85. GRB 260211A: SVOM/VT optical rebrightening at 20 days after the burst, SN candidate
  86. GRB 260303A: SVOM/VT optical observations
  87. GRB 260303A: SVOM/COLIBRÍ (FM-GFT) optical counterpart candidate
  88. EP260227a: Mondy optical observations
  89. EP260227a: SVOM/VT optical observation
  90. GRB 260228A: SVOM/VT optical upper limits
  91. EP260227A: 3.6m DOT optical afterglow detection
  92. EP260227a: likely GTC/OSIRIS+ redshift z = 2.714
  93. EP260227a: Liverpool Telescope observations
  94. GRB 260225A: SVOM/VT optical continued observations and upper limit
  95. EP/WXT trigger 01709258681 (EP260227a?): LCO candidate afterglow
  96. GRB 260223A: 7DT detection and Medium-band SED of Afterglow
  97. EP260214a: VLT/FORS2 optical observations
  98. GRB 260226A: CALET Gamma-Ray Burst Monitor detection
  99. EP260214a: VLA 6 GHz detection
  100. GRB 260225A: SVOM/VT optical observation

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