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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').
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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"

22854 results found.

  1. LIGO/Virgo/Kagra S250818k: STEP/T80N upper limits on 2025ulz
  2. LIGO/Virgo/KAGRA S250818k: 3 GHz MeerKAT observations of AT2025ulz
  3. IPN triangulation of GRB 250821B (long/bright)
  4. GRB 250821A: Kilonova-Catcher optical upper limits
  5. EP250821a: Swift/XRT counterpart fading
  6. GRB 250812A: SVOM/ECLAIRs refined analysis
  7. LIGO/Virgo/KAGRA S250818k: Pan-STARRS coverage of the skymap and candidate counterparts
  8. EP250821a: Swift/UVOT further observations.
  9. GRB 250821A: VLT/FORS2 Optical Observation
  10. GRB 250821B: SVOM/GRM observation
  11. EP250821a: SVOM/VT optical observation
  12. GRB 250821A: NOT z-band upper limit
  13. GRB 250821A: KAIT optical upper limit
  14. GRB 250821A: Swift-XRT refined Analysis
  15. LIGO/Virgo/KAGRA S250818k : Tautenburg observations, upper limits
  16. GRB 250821A: Enhanced Swift-XRT position
  17. GRB 250821A: Swift/UVOT Upper Limits
  18. EP250821a: Swift XRT and UVOT counterpart detection
  19. LIGO/Virgo/KAGRA S250818k: GOTO counterpart search and upper limits
  20. EP250821a: Preliminary analysis of the EP-WXT and EP-FXT observations
  21. GRB 250821A: LCOGT Optical Upper Limits
  22. GRB 250814A: CMO SAI and SAO RAS izJ observations.
  23. LIGO/Virgo/KAGRA S250818k: 10 GHz VLA observations of AT2025ulz
  24. GRB 250821A: Swift detection of a burst
  25. LIGO/Virgo/KAGRA S250818k: WFST pre-discovery limits and follow-up observations of AT 2025ulz
  26. LIGO/Virgo/KAGRA S250818k: EP/FXT observation of AT 2025ulz
  27. EP250821a: Einstein Probe detection of an X-ray transient
  28. GRB 250819A: SVOM/GRM observation of a possible “long” duration type I burst
  29. LIGO/Virgo/KAGRA S250818k: WINTER J-band observations of AT 2025ulz
  30. LIGO/Virgo/KAGRA S250818k: Pan-STARRS grizy-band imaging and photometry of AT2025ulz
  31. LIGO/Virgo/KAGRA S250818k: Swift observations of AT 2025ulz
  32. LIGO/Virgo/KAGRA S250818k: ATLAS pre-discovery limits for AT2025ulz
  33. GRB 250814A: Swift/UVOT Upper Limits
  34. GRB 250813B: Swift/UVOT Upper Limit
  35. IPN triangulation of GRB 250816A (short)
  36. IPN triangulation of GRB 250814C (short)
  37. IPN triangulation of GRB 250804B (short)
  38. GRB 250818B: Kilonova-Catcher optical afterglow detection
  39. LIGO/Virgo/KAGRA S250818k: AstroSat CZTI non-detection and upper limits
  40. LIGO/Virgo/KAGRA S250818k: Upper limits from Fermi-GBM Observations
  41. LIGO/Virgo/KAGRA S250818k: Updated Sky localization and EM Bright Classification
  42. LIGO/Virgo/KAGRA S250818k: Pan-STARRS pre-detection limits for AT2025ulz
  43. GRB 250818A: AstroSat CZTI detection
  44. LIGO/Virgo/KAGRA S250818k: Properties of the low-significance GW compact binary merger candidate potentially associated with AT 2025ulz
  45. GRB 250818B: Swift/UVOT Detection
  46. GRB 250818B: SAO RAS optical observations
  47. Swift GRB 250818A: Global MASTER-Net observations report
  48. GRB 250818B: KAIT optical observations
  49. GRB 250818A: Swift/UVOT Upper Limits
  50. GRB 250818A: Enhanced Swift-XRT position
  51. LIGO/Virgo/KAGRA S250818k: Coverage and upper limits from MAXI/GSC observations
  52. GRB 250814A: Further GRAWITA TNG NIR observations
  53. GRB 250818B: Swift-XRT afterglow detection
  54. GRB 250818B: GOTO optical counterpart candidate
  55. LIGO/Virgo/KAGRA S250818t: Identification of a GW compact binary merger candidate
  56. GRB 250818A: Swift detection of a burst
  57. sb25081602: Swift-XRT observations
  58. GRB 250816A: SVOM/GRM observation of a short burst
  59. SVOM/sb25081602: detection of a likely X-ray transient
  60. GRB 250813B: Liverpool Telescope optical upper limits
  61. GRB 250814A: Further COLIBRÍ optical upper limit
  62. GRB 250814A: detection of the afterglow candidate with Liverpool Telescope
  63. GRB 250814A: GRAWITA TNG NIR observations
  64. GRB 250814A: Mondy optical observations of the candidate counterpart to LVK S250814bg
  65. GRB 250813B: Calapai Observatory, Massa S. Giorgio (Messina), upper limit
  66. GRB250814A: TRT optical upper limits
  67. GRB 250814B: SVOM/GRM observation
  68. LIGO/Virgo/KAGRA S250813k: Swift XRT observations, 2 X-ray sources
  69. GRB 250814A: P200/WIRC observations of the afterglow candidate
  70. GRB 250814A: possible optical afterglow candidate at Spanish observatories
  71. GRB 250814A: KAIT optical upper limit
  72. GRB 250814A: Swift-XRT refined Analysis
  73. GRB 250814A: Possible afterglow candidate from P200/WIRC
  74. GRB 250813B: Fermi GBM Observation
  75. GRB 250814A: Optical observations with MDM Hiltner 2.4m telescope
  76. GRB 250814A: J-band upper limit from WINTER
  77. GRB 250813B: NOT observations of the optical afterglow
  78. GRB 250814A: COLIBRÍ optical upper limit
  79. LIGO/Virgo/KAGRA S250814bg: Identification of a GW compact binary merger candidate possibly associated with GRB 250814A detected by Fermi GBM and Swift BAT
  80. GRB 250814A: DDOTI Optical Upper Limit
  81. GRB 250814A: Swift detection of a burst coincident with a subthreshold GW trigger
  82. GRB 250813B: SVOM/COLIBRÍ (FM-GFT) optical observations
  83. GRB 250813B: SVOM detection of a bright long burst (Correction for GCN 41352).
  84. GRB 250813B: SVOM detection of a bright long burst
  85. EP250812a: Nickel optical upper limit
  86. EP250812a: NOT, NTT, and GS observations
  87. GRB 250812A: Swift/UVOT Detection
  88. EP250812a: COLIBRÍ detection of the VT candidate and evidence of flattening
  89. EP250812a: Liverpool Telescope upper limits
  90. EP250812a: refined analysis of the EP-WXT and EP-FXT observations
  91. LIGO/Virgo/KAGRA S250813k: Identification of a GW compact binary merger candidate
  92. EP 250812a: GOTO optical upper limit
  93. GRB 250812A: Kilonova-Catcher optical afterglow detection
  94. EP250812a: Swift-XRT counterpart detection
  95. GRB 250812A: SVOM/COLIBRÍ (FM-GFT) optical observations
  96. EP250812a: Einstein Probe detection of an X-ray transient
  97. GRB 250812A: Swift-XRT afterglow detection
  98. GRB 250812A: TRT likely optical counterpart detection
  99. LIGO/Virgo/KAGRA S250810ck: Updated Sky localization and EM Bright Classification
  100. GRB 250809A: Swift/UVOT Detection

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