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GCN Circulars

GCN Circulars are rapid bulletins submitted by and distributed to the community. 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').
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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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45698 results found.

  1. GRB 250823A: NOT optical observations
  2. LIGO/Virgo/KAGRA S250818k: CFH/MegaCam follow-up observation for AT2025ulz
  3. LIGO/Virgo/KAGRA S250818k: COLIBRÍ confirmation of rebrightening of AT2025ulz
  4. GRB 250823A: Fermi GBM Observation
  5. GRB 250818B: MeerKAT Detection
  6. GRB 250823A: Enhanced Swift-XRT position
  7. GRB 250823A: LCOGT Optical Detection
  8. GRB 250823A: BOOTES6/DPRT early optical detection
  9. GRB 250823A: Liverpool Telescope optical detection
  10. GRB 250823A: Swift detection of a burst
  11. GRB 250823A: Fermi GBM Final Real-time Localization
  12. Swift GRB250823.84: Global MASTER-Net observations report
  13. Konus-Wind detection of GRB 250821B
  14. LIGO/Virgo/KAGRA S250818k: Rebrightening detected with Gemini/GMOS
  15. LIGO/Virgo/KAGRA S250818k: HST nIR detection of AT 2025ulz
  16. LIGO/Virgo/KAGRA S250818k: J-GEM follow-up observation for AT2025ulz
  17. LIGO/Virgo/KAGRA S250818k: PRIME nIR observations of AT2025ulz
  18. LIGO/Virgo/KAGRA S250818k: JinShan optical observations of AT2025ulz
  19. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Optical Detection of AT2025ulz
  20. LIGO/Virgo/Kagra S250818k: STEP/T80N upper limits on 2025ulz
  21. LIGO/Virgo/KAGRA S250818k: 3 GHz MeerKAT observations of AT2025ulz
  22. GRB 250806A: Gemini observations of host galaxy candidate
  23. IPN triangulation of GRB 250821B (long/bright)
  24. GRB 250821A: Kilonova-Catcher optical upper limits
  25. EP250821a: Swift/XRT counterpart fading
  26. GRB 250812A: SVOM/ECLAIRs refined analysis
  27. GRB 250821A: Swift-BAT refined analysis
  28. LIGO/Virgo/KAGRA S250818k: Pan-STARRS coverage of the skymap and candidate counterparts
  29. LIGO/Virgo/KAGRA S250818k: NOT optical observations of AT2025ulz
  30. EP250821a: Swift/UVOT further observations.
  31. EP250821a: VLT X-shooter spectroscopic redshift z = 0.577
  32. LIGO/Virgo/KAGRA S250818k: GRAWITA TNG NIR observations of AT2025ulz
  33. GRB 250821A: VLT/FORS2 Optical Observation
  34. GRB 250821A: GECAM-B detection
  35. GRB 250821B: SVOM/GRM observation
  36. EP250821a: SVOM/VT optical observation
  37. Fermi GRB 250821B: Global MASTER-Net observations report
  38. GRB 250821A: NOT z-band upper limit
  39. GRB 250821C: Fermi GBM Final Real-time Localization
  40. GRB 250821A: KAIT optical upper limit
  41. LIGO/Virgo/KAGRA S250818k: Continued fading and reddening of AT2025ulz from Keck/LRIS imaging observations
  42. GRB 250821A: Swift-XRT refined Analysis
  43. Swift GRB 250821A: Global MASTER-Net observations report
  44. GRB 250821B: Fermi GBM Detection
  45. LIGO/Virgo/KAGRA S250818k: ENGRAVE observations of AT 2025ulz
  46. GRB 250821B: BALROG localization (Fermi Trigger / GRB 250821672)
  47. LIGO/Virgo/KAGRA S250818k : Tautenburg observations, upper limits
  48. GRB 250821B: Fermi GBM Final Localization of a Bright Burst
  49. GRB 250821A: Enhanced Swift-XRT position
  50. GRB 250821A: Swift/UVOT Upper Limits
  51. EP250821a: Rapidly fading optical source detected in Las Cumbres followup
  52. EP250821a: Swift XRT and UVOT counterpart detection
  53. LIGO/Virgo/KAGRA S250818k: GOTO counterpart search and upper limits
  54. EP250821a: Preliminary analysis of the EP-WXT and EP-FXT observations
  55. GRB 250821A: LCOGT Optical Upper Limits
  56. GRB 250814A: CMO SAI and SAO RAS izJ observations.
  57. LIGO/Virgo/KAGRA S250818k: 10 GHz VLA observations of AT2025ulz
  58. GRB 250821A: Prompt enhanced Swift-XRT position
  59. GRB 250821A: Swift detection of a burst
  60. LIGO/Virgo/KAGRA S250818k: WFST pre-discovery limits and follow-up observations of AT 2025ulz
  61. LIGO/Virgo/KAGRA S250818k: EP/FXT observation of AT 2025ulz
  62. EP250821a: Einstein Probe detection of an X-ray transient
  63. GRB 250819A: SVOM/GRM observation of a possible “long” duration type I burst
  64. GRB 250819A: Insight-HXMT detection
  65. LIGO/Virgo/KAGRA S250818k: WINTER J-band observations of AT 2025ulz
  66. GRB 250818B: 10 GHz VLA detection
  67. LIGO/Virgo/KAGRA S250818k: Pan-STARRS grizy-band imaging and photometry of AT2025ulz
  68. LIGO/Virgo/KAGRA S250818k: Swift observations of AT 2025ulz
  69. LIGO/Virgo/KAGRA S250818k: Multi-band Gemini GMOS Detections
  70. LIGO/Virgo/KAGRA S250818k: ATLAS pre-discovery limits for AT2025ulz
  71. GRB 250814A: Swift/UVOT Upper Limits
  72. GRB 250813B: Swift/UVOT Upper Limit
  73. IPN triangulation of GRB 250816A (short)
  74. IPN triangulation of GRB 250814C (short)
  75. IPN triangulation of GRB 250804B (short)
  76. GRB 250818B: FTW optical and NIR observations show reddening of the counterpart
  77. GRB 250818B: Kilonova-Catcher optical afterglow detection
  78. LIGO/Virgo/KAGRA S250818k: AstroSat CZTI non-detection and upper limits
  79. GRB 250818B: Liverpool Telescope optical detections
  80. LIGO/Virgo/KAGRA S250818k: Upper limits from Fermi-GBM Observations
  81. LIGO/Virgo/KAGRA S250818k: Updated Sky localization and EM Bright Classification
  82. LIGO/Virgo/KAGRA S250818k: Pan-STARRS pre-detection limits for AT2025ulz
  83. GRB 250818A: AstroSat CZTI detection
  84. LIGO/Virgo/KAGRA S250818k: Properties of the low-significance GW compact binary merger candidate potentially associated with AT 2025ulz
  85. LIGO/Virgo/KAGRA S250818k: Keck I LRIS spectroscopy of ZTF25abjmnps (AT2025ulz)
  86. GRB 250818B: Swift/UVOT Detection
  87. Fermi Gamma-ray Burst Monitor trigger 777342746/250820022 is not a GRB
  88. LIGO/Virgo/KAGRA S250818k: FTW Fast reddening of AT 2025ulz
  89. GRB 250820A: Fermi GBM Final Real-time Localization
  90. GRB 250818B: optical afterglow detection with Lesedi (GOTO25fzq)
  91. GRB 250818B: TRT Optical Observation
  92. Fermi GRB 250816A: Global MASTER-Net observations report
  93. GRB 250818B: SAO RAS optical observations
  94. Swift GRB 250818A: Global MASTER-Net observations report
  95. GRB 250818B: NOT optical observations
  96. GRB 250818A: Swift-XRT refined Analysis
  97. GRB 250818B: EP-FXT counterpart detection
  98. GRB 250818A: Swift-BAT refined analysis
  99. Fermi Gamma-ray Burst Monitor trigger 777251788/250818970 is not a GRB
  100. LIGO/Virgo/KAGRA S250818k: FTW optical and NIR observations of AT 2025ulz

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