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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"
body:"GRB"
submitter:"Judith Racusin"

45645 results found.

  1. EP250827a: GOTO observation of the optical afterglow
  2. GRB 250826A: SVOM/GRM observation
  3. GRB 250827A: Fermi GBM Final Real-time Localization
  4. EP250827A: An optical rebrightening was detected by LCO.
  5. EP250827a: Swift-XRT counterpart detection
  6. LIGO/Virgo/KAGRA S250827l: Updated Sky localization
  7. The EP-WXT trigger 01709200800 is likely a flaring star
  8. EP250827a: TRT optical observations
  9. EP250827a: BOOTES-7 early optical dectection
  10. EP250827a / GRB 250827A: MASTER-OAFA OT observation
  11. EP250827a: Gemini-South redshift z = 1.613
  12. EP250827a: Global MASTER-Net observations report
  13. EP250827a: Las Cumbres independent detection of the optical counterpart
  14. EP250827a: Gemini-South optical counterpart detection
  15. EP250827a: Einstein Probe detection of an X-ray transient
  16. LIGO/Virgo/KAGRA S250827l: Identification of a GW compact binary merger candidate
  17. Fermi GRB 250826A: Global MASTER-Net observations report
  18. GRB 250806A: HiPERCAM/GTC limits on a possible supernova
  19. EP250821a: Gemini GMOS Redshift Confirmation
  20. LIGO/Virgo/KAGRA S250818k: SAO RAS BTA z-band observations of AT2025ulz
  21. Fermi trigger No 777883624: Global MASTER-Net observations report
  22. Fermi Gamma-ray Burst Monitor trigger 777883624/250826283 is not a GRB
  23. GRB 250826A: Fermi GBM Final Real-time Localization
  24. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Confirmation of Rebrightening of AT2025ulz
  25. Fermi GRB 250824B: Global MASTER-Net observations report
  26. LIGO/Virgo/KAGRA S250818k: VLA upper limits on AT2025ulz
  27. LIGO/Virgo/KAGRA S250818k: nature of the AT2025ulz/ZTF25abjmnnps OT
  28. LIGO/Virgo/KAGRA S250818k: Pan-STARRS imaging confirms re-brightening of SN2025ulz
  29. GRB 250823A: Swift-BAT refined analysis
  30. LIGO/Virgo/KAGRA S250818k: Continued Keck I LRIS spectroscopy of ZTF25abjmnps (AT2025ulz)
  31. GRB 250821B: AstroSat CZTI detection
  32. GRB 250819A: AstroSat CZTI detection
  33. LIGO/Virgo/KAGRA S250818k: FTW Observations Show Continued Reddening of AT 2025ulz
  34. LIGO/Virgo/KAGRA S250818k: MASTER predicovery limits of the AT2025ulz/ZTF25abjmnps KN candidate
  35. GRB 250821B: Insight-HXMT detection
  36. LIGO/Virgo/KAGRA S250818k: ENGRAVE observations of SN 2025ulz as a type II supernova
  37. GRB 250823A: Swift-XRT refined Analysis
  38. EP250821a: MeerKAT radio counterpart
  39. EP triggers 01709200706 and 01709200707: GOTO confirmation of flaring stars
  40. LIGO/Virgo/KAGRA S250818k: Swift Observations of AT 2025ulz - Second Epoch
  41. GRB 250824B: Fermi GBM Final Real-time Localization
  42. The EP-WXT trigger 01709200707 is likely a flaring star
  43. GRB 250823A: COLIBRÍ optical observations
  44. The EP-WXT trigger 01709200706 is likely a flaring star
  45. GRB 250823A: SVOM/VT optical observation
  46. GRB 250824A: Fermi GBM Final Real-time Localization
  47. GRB 250823A: Swift/UVOT Detection
  48. GRB 250823A: NOT optical observations
  49. LIGO/Virgo/KAGRA S250818k: CFH/MegaCam follow-up observation for AT2025ulz
  50. LIGO/Virgo/KAGRA S250818k: COLIBRÍ confirmation of rebrightening of AT2025ulz
  51. GRB 250823A: Fermi GBM Observation
  52. GRB 250818B: MeerKAT Detection
  53. GRB 250823A: Enhanced Swift-XRT position
  54. GRB 250823A: LCOGT Optical Detection
  55. GRB 250823A: BOOTES6/DPRT early optical detection
  56. GRB 250823A: Liverpool Telescope optical detection
  57. GRB 250823A: Swift detection of a burst
  58. GRB 250823A: Fermi GBM Final Real-time Localization
  59. Swift GRB250823.84: Global MASTER-Net observations report
  60. Konus-Wind detection of GRB 250821B
  61. LIGO/Virgo/KAGRA S250818k: Rebrightening detected with Gemini/GMOS
  62. LIGO/Virgo/KAGRA S250818k: HST nIR detection of AT 2025ulz
  63. LIGO/Virgo/KAGRA S250818k: J-GEM follow-up observation for AT2025ulz
  64. LIGO/Virgo/KAGRA S250818k: PRIME nIR observations of AT2025ulz
  65. LIGO/Virgo/KAGRA S250818k: JinShan optical observations of AT2025ulz
  66. LIGO/Virgo/KAGRA S250818k: GTC/OSIRIS Optical Detection of AT2025ulz
  67. LIGO/Virgo/Kagra S250818k: STEP/T80N upper limits on 2025ulz
  68. LIGO/Virgo/KAGRA S250818k: 3 GHz MeerKAT observations of AT2025ulz
  69. GRB 250806A: Gemini observations of host galaxy candidate
  70. IPN triangulation of GRB 250821B (long/bright)
  71. GRB 250821A: Kilonova-Catcher optical upper limits
  72. EP250821a: Swift/XRT counterpart fading
  73. GRB 250812A: SVOM/ECLAIRs refined analysis
  74. GRB 250821A: Swift-BAT refined analysis
  75. LIGO/Virgo/KAGRA S250818k: Pan-STARRS coverage of the skymap and candidate counterparts
  76. LIGO/Virgo/KAGRA S250818k: NOT optical observations of AT2025ulz
  77. EP250821a: Swift/UVOT further observations.
  78. EP250821a: VLT X-shooter spectroscopic redshift z = 0.577
  79. LIGO/Virgo/KAGRA S250818k: GRAWITA TNG NIR observations of AT2025ulz
  80. GRB 250821A: VLT/FORS2 Optical Observation
  81. GRB 250821A: GECAM-B detection
  82. GRB 250821B: SVOM/GRM observation
  83. EP250821a: SVOM/VT optical observation
  84. Fermi GRB 250821B: Global MASTER-Net observations report
  85. GRB 250821A: NOT z-band upper limit
  86. GRB 250821C: Fermi GBM Final Real-time Localization
  87. GRB 250821A: KAIT optical upper limit
  88. LIGO/Virgo/KAGRA S250818k: Continued fading and reddening of AT2025ulz from Keck/LRIS imaging observations
  89. GRB 250821A: Swift-XRT refined Analysis
  90. Swift GRB 250821A: Global MASTER-Net observations report
  91. GRB 250821B: Fermi GBM Detection
  92. LIGO/Virgo/KAGRA S250818k: ENGRAVE observations of AT 2025ulz
  93. GRB 250821B: BALROG localization (Fermi Trigger / GRB 250821672)
  94. LIGO/Virgo/KAGRA S250818k : Tautenburg observations, upper limits
  95. GRB 250821B: Fermi GBM Final Localization of a Bright Burst
  96. GRB 250821A: Enhanced Swift-XRT position
  97. GRB 250821A: Swift/UVOT Upper Limits
  98. EP250821a: Rapidly fading optical source detected in Las Cumbres followup
  99. EP250821a: Swift XRT and UVOT counterpart detection
  100. LIGO/Virgo/KAGRA S250818k: GOTO counterpart search and upper limits

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