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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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submitter:"Judith Racusin"

43892 results found.

  1. Swift GRB250823.84: Global MASTER-Net observations report
  2. Konus-Wind detection of GRB 250821B
  3. LIGO/Virgo/KAGRA S250818k: Rebrightening detected with Gemini/GMOS
  4. LIGO/Virgo/KAGRA S250818k: HST nIR detection of AT 2025ulz
  5. LIGO/Virgo/KAGRA S250818k: J-GEM follow-up observation for AT2025ulz
  6. LIGO/Virgo/KAGRA S250818k: PRIME nIR observations of AT2025ulz
  7. LIGO/Virgo/KAGRA S250818k: JinShan optical observations of AT2025ulz
  8. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Optical Detection of AT2025ulz
  9. LIGO/Virgo/Kagra S250818k: STEP/T80N upper limits on 2025ulz
  10. LIGO/Virgo/KAGRA S250818k: 3 GHz MeerKAT observations of AT2025ulz
  11. GRB 250806A: Gemini observations of host galaxy candidate
  12. IPN triangulation of GRB 250821B (long/bright)
  13. GRB 250821A: Kilonova-Catcher optical upper limits
  14. EP250821a: Swift/XRT counterpart fading
  15. GRB 250812A: SVOM/ECLAIRs refined analysis
  16. GRB 250821A: Swift-BAT refined analysis
  17. LIGO/Virgo/KAGRA S250818k: Pan-STARRS coverage of the skymap and candidate counterparts
  18. LIGO/Virgo/KAGRA S250818k: NOT optical observations of AT2025ulz
  19. EP250821a: VLT X-shooter spectroscopic redshift z = 0.577
  20. LIGO/Virgo/KAGRA S250818k: GRAWITA TNG NIR observations of AT2025ulz
  21. GRB 250821A: GECAM-B detection
  22. GRB 250821B: SVOM/GRM observation
  23. EP250821a: SVOM/VT optical observation
  24. Fermi GRB 250821B: Global MASTER-Net observations report
  25. GRB 250821A: NOT z-band upper limit
  26. GRB 250821C: Fermi GBM Final Real-time Localization
  27. GRB 250821A: KAIT optical upper limit
  28. LIGO/Virgo/KAGRA S250818k: Continued fading and reddening of AT2025ulz from Keck/LRIS imaging observations
  29. GRB 250821A: Swift-XRT refined Analysis
  30. Swift GRB 250821A: Global MASTER-Net observations report
  31. GRB 250821B: Fermi GBM Detection
  32. LIGO/Virgo/KAGRA S250818k: ENGRAVE observations of AT 2025ulz
  33. GRB 250821B: BALROG localization (Fermi Trigger / GRB 250821672)
  34. LIGO/Virgo/KAGRA S250818k : Tautenburg observations, upper limits
  35. GRB 250821B: Fermi GBM Final Localization of a Bright Burst
  36. GRB 250821A: Enhanced Swift-XRT position
  37. EP250821a: Rapidly fading optical source detected in Las Cumbres followup
  38. EP250821a: Swift XRT and UVOT counterpart detection
  39. LIGO/Virgo/KAGRA S250818k: GOTO counterpart search and upper limits
  40. EP250821a: Preliminary analysis of the EP-WXT and EP-FXT observations
  41. GRB 250821A: LCOGT Optical Upper Limits
  42. GRB 250814A: CMO SAI and SAO RAS izJ observations.
  43. LIGO/Virgo/KAGRA S250818k: 10 GHz VLA observations of AT2025ulz
  44. GRB 250821A: Prompt enhanced Swift-XRT position
  45. GRB 250821A: Swift detection of a burst
  46. LIGO/Virgo/KAGRA S250818k: WFST pre-discovery limits and follow-up observations of AT 2025ulz
  47. LIGO/Virgo/KAGRA S250818k: EP/FXT observation of AT 2025ulz
  48. EP250821a: Einstein Probe detection of an X-ray transient
  49. GRB 250819A: SVOM/GRM observation of a possible “long” duration type I burst
  50. GRB 250819A: Insight-HXMT detection
  51. LIGO/Virgo/KAGRA S250818k: WINTER J-band observations of AT 2025ulz
  52. GRB 250818B: 10 GHz VLA detection
  53. LIGO/Virgo/KAGRA S250818k: Pan-STARRS grizy-band imaging and photometry of AT2025ulz
  54. LIGO/Virgo/KAGRA S250818k: Swift observations of AT 2025ulz
  55. LIGO/Virgo/KAGRA S250818k: Multi-band Gemini GMOS Detections
  56. LIGO/Virgo/KAGRA S250818k: ATLAS pre-discovery limits for AT2025ulz
  57. IPN triangulation of GRB 250816A (short)
  58. IPN triangulation of GRB 250814C (short)
  59. IPN triangulation of GRB 250804B (short)
  60. GRB 250818B: FTW optical and NIR observations show reddening of the counterpart
  61. GRB 250818B: Kilonova-Catcher optical afterglow detection
  62. LIGO/Virgo/KAGRA S250818k: AstroSat CZTI non-detection and upper limits
  63. GRB 250818B: Liverpool Telescope optical detections
  64. LIGO/Virgo/KAGRA S250818k: Upper limits from Fermi-GBM Observations
  65. LIGO/Virgo/KAGRA S250818k: Updated Sky localization and EM Bright Classification
  66. LIGO/Virgo/KAGRA S250818k: Pan-STARRS pre-detection limits for AT2025ulz
  67. GRB 250818A: AstroSat CZTI detection
  68. LIGO/Virgo/KAGRA S250818k: Properties of the low-significance GW compact binary merger candidate potentially associated with AT 2025ulz
  69. LIGO/Virgo/KAGRA S250818k: Keck I LRIS spectroscopy of ZTF25abjmnps (AT2025ulz)
  70. Fermi Gamma-ray Burst Monitor trigger 777342746/250820022 is not a GRB
  71. LIGO/Virgo/KAGRA S250818k: FTW Fast reddening of AT 2025ulz
  72. GRB 250820A: Fermi GBM Final Real-time Localization
  73. GRB 250818B: optical afterglow detection with Lesedi (GOTO25fzq)
  74. GRB 250818B: TRT Optical Observation
  75. Fermi GRB 250816A: Global MASTER-Net observations report
  76. GRB 250818B: SAO RAS optical observations
  77. Swift GRB 250818A: Global MASTER-Net observations report
  78. GRB 250818B: NOT optical observations
  79. GRB 250818A: Swift-XRT refined Analysis
  80. GRB 250818B: EP-FXT counterpart detection
  81. GRB 250818A: Swift-BAT refined analysis
  82. Fermi Gamma-ray Burst Monitor trigger 777251788/250818970 is not a GRB
  83. LIGO/Virgo/KAGRA S250818k: FTW optical and NIR observations of AT 2025ulz
  84. GRB 250818C: Fermi GBM Final Real-time Localization
  85. GRB 250818B: Keck redshift of the optical afterglow
  86. Fermi trigger No 776849714: Global MASTER-Net observations report
  87. GRB 250818B: KAIT optical observations
  88. LIGO/Virgo/KAGRA S250818t: Updated Sky localization
  89. LIGO/Virgo/KAGRA S250818k: Candidates from the Zwicky Transient Facility
  90. GRB 250818A: Enhanced Swift-XRT position
  91. GRB 250813B: SVOM/ECLAIRs refined analysis
  92. GRB 250818A: Fermi GBM Observation
  93. LIGO/Virgo/KAGRA S250818k: Coverage and upper limits from MAXI/GSC observations
  94. GRB 250818B: SVOM/VT optical observation
  95. GRB 250814A: Further GRAWITA TNG NIR observations
  96. GRB 250818B: Swift-XRT afterglow detection
  97. GRB 250818B: GOTO optical counterpart candidate
  98. GRB 250818B: SVOM detection of a short burst
  99. LIGO/Virgo/KAGRA S250818t: Identification of a GW compact binary merger candidate
  100. GRB 250818A: Swift detection of a burst

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